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                                                                     EXHIBIT 2B
                             STOCK OPTION AGREEMENT


      THIS STOCK OPTION AGREEMENT (this "Agreement") is made and entered into
as of May 8, 1997, by and between Magna Bancorp, Inc., a Delaware corporation
("Issuer"), and Union Planters Corporation, a Tennessee corporation
("Grantee").

      WHEREAS, Grantee and Issuer have entered into that certain Agreement and
Plan of Reorganization, dated as of May 8, 1997 (the "Merger Agreement"),
providing for, among other things, the merger of a wholly owned Subsidiary of
Grantee with and into Issuer, with Grantee as the surviving entity; and

      WHEREAS, as a condition and inducement to Grantee's execution of the
Merger Agreement, Grantee has required that Issuer agree, and Issuer has
agreed, to grant Grantee the Option (as defined below);

      NOW, THEREFORE, in consideration of the respective representations,
warranties, covenants and agreements set forth herein and in the Merger
Agreement, and intending to be legally bound hereby, Issuer and Grantee agree
as follows:

      1.     DEFINED TERMS.  Capitalized terms which are used but not defined
herein shall have the meanings ascribed to such terms in the Merger Agreement.

      2.     GRANT OF OPTION.  Subject to the terms and conditions set forth
herein, Issuer hereby grants to Grantee an irrevocable option (the "Option") to
purchase up to 2,737,000 shares (as adjusted as set forth herein, the "Option
Shares," which shall include the Option Shares before and after any transfer of
such Option Shares) of common stock, $0.01 par value per share ("Issuer Common
Stock"), of Issuer at a purchase price per Option Share (subject to adjustment
as set forth herein, the "Purchase Price") equal to $17.50; provided, however,
that in no event shall the number of shares of Issuer Common Stock for which
this Option is exercisable exceed 19.9% of the Issuer's issued and outstanding
shares of Issuer Common stock without giving effect to any shares subject to or
issued pursuant to the Option.

      3.     EXERCISE OF OPTION.

             (a)   Provided that (i) Grantee or Holder (as hereinafter
defined), as applicable, shall not be in material breach of its agreements or
covenants contained in this Agreement or the Merger Agreement, and (ii) no
preliminary or permanent injunction or other order against the delivery of
shares covered by the Option issued by any court of competent jurisdiction in
the United States shall be in effect, Holder may exercise the Option, in whole
or in part, at any time and from time to time following the occurrence of a
Purchase Event; provided that the Option shall terminate and be of no further
force and effect upon the earliest to occur of (A) the Effective Time, (B)
termination of the Merger Agreement in accordance with the terms thereof prior
to the occurrence of a Purchase Event or a Preliminary Purchase Event (other
than a termination of the Merger Agreement by Grantee pursuant to (i) Section
10.1(b) thereof (but only if such
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termination was a result of a willful breach by Issuer) or (ii) Section 10.1(c)
thereof (each a "Default Termination")), (C) 12 months after a Default
Termination, and (D) 12 months after any termination of the Merger Agreement
(other than a Default Termination) following the occurrence of a Purchase Event
or a Preliminary Purchase Event; provided further, that any purchase of shares
upon exercise of the Option shall be subject to compliance with applicable law,
including, without limitation, the Bank Holding Company Act of 1956, as amended
(the "BHC Act"), and the Home Owners' Loan Act of 1933, as amended (the
"HOLA").  The term "Holder" shall mean the holder or holders of the Option from
time to time, and which initially is the Grantee.  The rights set forth in
Section 8 shall terminate when the right to exercise the Option terminates
(other than as a result of a complete exercise of the Option) as set forth
herein.

             (b)   As used herein, a "Purchase Event" means any of the
following events subsequent to the date of this Agreement:

                   (i)    without Grantee's prior written consent, Issuer shall
      have authorized, recommended, publicly proposed or publicly announced an
      intention to authorize, recommend or propose, or entered into an
      agreement with any person (other than Grantee or any Subsidiary of
      Grantee) to effect an Acquisition Transaction (as defined below).  As
      used herein, the term Acquisition Transaction shall mean (A) a merger,
      consolidation or similar transaction involving Issuer or any of its
      Subsidiaries (other than transactions solely between Issuer's
      Subsidiaries), (B) except as permitted pursuant to Section 7.1 of the
      Merger Agreement, the disposition, by sale, lease, exchange or otherwise,
      of Assets of Issuer or any of its Subsidiaries representing in either
      case 25% or more of the consolidated assets of Issuer and its
      Subsidiaries, or (C) the issuance, sale or other disposition of
      (including by way of merger, consolidation, share exchange or any similar
      transaction) securities representing 25% or more of the voting power of
      Issuer or any of its Subsidiaries (any of the foregoing, an "Acquisition
      Transaction"); or

                   (ii)   any person (other than Grantee or any Subsidiary of
      Grantee) shall have acquired beneficial ownership (as such term is
      defined in Rule 13d-3 promulgated under the Exchange Act) of or the right
      to acquire beneficial ownership of, or any "group" (as such term is
      defined under the Exchange Act), other than a group of which Grantee or
      any of its Subsidiaries of Grantee is a member, shall have been formed
      which beneficially owns or has the right to acquire beneficial ownership
      of, 25% or more of the then-outstanding shares of Issuer Common Stock.

             (c)   As used herein, a "Preliminary Purchase Event" means any of
the following events:

                   (i)    any person (other than Grantee or any Subsidiary of
      Grantee) shall have commenced (as such term is defined in Rule 14d-2
      under the Exchange Act), or shall have filed a registration statement
      under the Securities Act with respect to, a tender offer or exchange
      offer to purchase any shares of Issuer Common Stock such that, upon
      consummation of such offer, such person would own or control 25% or more
      of the then-

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      outstanding shares of Issuer Common Stock (such an offer being referred
      to herein as a "Tender Offer" or an "Exchange Offer," respectively); or

                   (ii)   the holders of Issuer Common Stock shall not have
      approved the Merger Agreement at the meeting of such shareholders held
      for the purpose of voting on the Merger Agreement, such meeting shall not
      have been held or shall have been canceled prior to termination of the
      Merger Agreement, or Issuer's Board of Directors shall have withdrawn or
      modified in a manner adverse to Grantee the recommendation of Issuer's
      Board of Directors with respect to the Merger Agreement, in each case
      after it shall have been publicly announced that any person (other than
      Grantee or any Subsidiary of Grantee) shall have (A) made a proposal to
      engage in an Acquisition Transaction, (B) commenced a Tender Offer or
      filed a registration statement under the Securities Act with respect to
      an Exchange Offer, or (C) filed an application (or given a notice),
      whether in draft or final form, under any federal or state statute or
      regulation (including a notice filed under the HSR Act and an application
      or notice filed under the BHC Act, the HOLA, the Bank Merger Act, or the
      Change in Bank Control Act of 1978) seeking the Consent to an Acquisition
      Transaction from any federal or state governmental or regulatory
      authority or agency.

As used in this Agreement, "person" shall have the meaning specified in
Sections 3(a)(9) and 13(d)(3) of the Exchange Act.

             (d)   In the event Holder wishes to exercise the Option, it shall
send to Issuer a written notice (the date of which being herein referred to as
the "Notice Date") specifying (i) the total number of Option Shares it intends
to purchase pursuant to such exercise and (ii) a place and date not earlier
than three business days nor later than 15 business days from the Notice Date
for the closing (the "Closing") of such purchase (the "Closing Date").  If
prior Consent of any governmental or regulatory agency or authority is required
in connection with such purchase, Issuer shall cooperate with Holder in the
filing of the required notice or application for such Consent and the obtaining
of such Consent and the Closing shall occur immediately following receipt of
such Consents (and expiration of any mandatory waiting periods).

             (e)   Notwithstanding any other provision of this Agreement to the
contrary, in no event shall:

                   (i) Holder's (taking into account all other Holders) Total
      Profit (as defined below) exceed $15 million and, if it otherwise would
      exceed such amount, Holder, at its sole election, shall either (A) reduce
      the number of shares of Issuer Common Stock subject to the Option, (B)
      deliver to Issuer for cancellation Option Shares previously purchased by
      Holder, (C) pay cash to Issuer, or (D) any combination of the foregoing,
      so that Holder's actually realized Total Profit shall not exceed $15
      million after taking into account the foregoing actions; and

                   (ii)   the Option be exercised for a number of shares of
      Issuer Common Stock as would, as of the date of exercise, result in a
      Notional Total Profit (as defined below) of





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      more than $15 million; provided, that nothing in this clause (ii) shall
      restrict any exercise of the Option permitted hereby on any subsequent
      date.

As used in this Agreement, the term "Total Profit" shall mean the aggregate sum
(prior to the payment of taxes) of the following:  (i) the amount received by
Holder pursuant to Issuer's repurchase of the Option (or any portion thereof)
pursuant to Section 8; (ii) (x) the amount received by Holder pursuant to
Issuer's repurchase of Option Shares pursuant to Section 8, less (y) Holder's
purchase price for such Option Shares; (iii) (x) the net cash amounts received
by Holder pursuant to the sale of Option Shares (or any other securities into
which such Option Shares shall be converted or exchanged) to any unaffiliated
person, less (y) Holder's purchase price of such Option Shares; and (iv) any
amounts received by Grantee on the transfer of the Option (or any portion
thereof) to any unaffiliated person.

As used in this Agreement, the term "Notional Total Profit" with respect to any
number of shares of Issuer Common Stock as to which Holder may propose to
exercise the Option shall be the Total Profit determined as of the date of such
proposed exercise, assuming that the Option were exercised on such date for
such number of shares and assuming that such shares, together with all other
Option Shares held by Holder and its affiliates as of such date, were sold for
cash at the closing sale price per share of Issuer Common Stock as quoted on
the Nasdaq National Market (or, if Issuer Common Stock is not then quoted on
the Nasdaq National Market, the highest bid price per share as quoted on the
principal trading market or securities exchange on which such shares are traded
as reported by a recognized source chosen by Holder) as of the close of
business on the preceding trading day (less customary brokerage commissions).

             (f)   Grantee agrees, promptly following any exercise of all or
any portion of the Option, and subject to its rights under Section 8, to use
commercially reasonable efforts promptly to maximize the value of Option Shares
purchased, taking into account market conditions, the number of Option Shares,
the potential negative impact of substantial sales on the market price for
Issuer Common Stock, and availability of an effective registration statement to
permit public sale of Option Shares.

      4.     PAYMENT AND DELIVERY OF CERTIFICATES.

             (a)   On each Closing Date, Holder shall (i) pay to Issuer, in
immediately available funds by wire transfer to a bank account designated by
Issuer, an amount equal to the Purchase Price multiplied by the number of
Option Shares to be purchased on such Closing Date, and (ii) present and
surrender this Agreement to the Issuer at the address of the Issuer specified
in Section 13(f) hereof.

             (b)   At each Closing, simultaneously with the delivery of
immediately available funds and surrender of this Agreement as provided in
Section 4(a), (i) Issuer shall deliver to Holder (A) a certificate or
certificates representing the Option Shares to be purchased at such Closing,
which Option Shares shall be free and clear of all liens, claims, charges and
encumbrances of any kind whatsoever and subject to no pre-emptive rights, and
(B) if the Option is exercised in part only, an executed new agreement with the
same terms as this Agreement evidencing the right to





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purchase the balance of the shares of Issuer Common Stock purchasable
hereunder, and (ii) Holder shall deliver to Issuer a letter agreeing that
Holder shall not offer to sell or otherwise dispose of such Option Shares in
violation of applicable federal and state law or of the provisions of this
Agreement.

             (c)   In addition to any other legend that is required by
applicable law, certificates for the Option Shares delivered at each Closing
shall be endorsed with a restrictive legend which shall read substantially as
follows:

      THE TRANSFER OF THE STOCK REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO
      RESTRICTIONS ARISING UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND
      PURSUANT TO THE TERMS OF A STOCK OPTION AGREEMENT DATED AS OF MAY 8,
      1997.  A COPY OF SUCH AGREEMENT WILL BE PROVIDED TO THE HOLDER HEREOF
      WITHOUT CHARGE UPON RECEIPT BY THE ISSUER OF A WRITTEN REQUEST THEREFOR.

It is understood and agreed that the above legend shall be removed by delivery
of substitute certificate(s) without such legend if Holder shall have delivered
to Issuer a copy of a letter from the staff of the SEC, or an opinion of
counsel in form and substance reasonably satisfactory to Issuer and its
counsel, to the effect that such legend is not required for purposes of the
Securities Act.

      5.     REPRESENTATIONS AND WARRANTIES OF ISSUER.  Issuer hereby
represents and warrants to Grantee as follows:

             (a)   Issuer has all requisite corporate power and authority to
      enter into this Agreement and, subject to any approvals referred to
      herein, to consummate the transactions contemplated hereby.  The
      execution and delivery of this Agreement and the consummation of the
      transactions contemplated hereby have been duly authorized by all
      necessary corporate action on the part of Issuer.  This Agreement has
      been duly executed and delivered by Issuer.


             (b)   Issuer has taken all necessary corporate and other action to
      authorize and reserve and to permit it to issue, and, at all times from
      the date hereof until the obligation to deliver Issuer Common Stock upon
      the exercise of the Option terminates, will have reserved for issuance,
      upon exercise of the Option, the number of shares of Issuer Common Stock
      necessary for Holder to exercise the Option, and Issuer will take all
      necessary corporate action to authorize and reserve for issuance all
      additional shares of Issuer Common Stock or other securities which may be
      issued pursuant to Section 7 upon exercise of the Option.  The shares of
      Issuer Common Stock to be issued upon due exercise of the Option,
      including all additional shares of Issuer Common Stock or other
      securities which may be issuable pursuant to Section 7, upon issuance
      pursuant hereto, shall be duly and validly issued, fully paid, and
      nonassessable, and shall be delivered free and clear of all liens,
      claims, charges,





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      and encumbrances of any kind or nature whatsoever, including any
      preemptive rights of any shareholder of Issuer.

      6.     REPRESENTATIONS AND WARRANTS OF GRANTEE.  Grantee hereby
represents and warrants to Issuer that:

             (a)   Grantee has all requisite corporate power and authority to
      enter into this Agreement and, subject to any approvals or consents
      referred to herein, to consummate the transactions contemplated hereby.
      The execution and delivery of this Agreement and the consummation of the
      transactions contemplated hereby have been duly authorized by all
      necessary corporate action on the part of Grantee.  This Agreement has
      been duly executed and delivered by Grantee.

             (b)   This Option is not being, and any Option Shares or other
      securities acquired by Grantee upon exercise of the Option will not be,
      acquired with a view to the public distribution thereof and will not be
      transferred or otherwise disposed of except in a transaction registered
      or exempt from registration under the Securities Laws.

      7.     ADJUSTMENT UPON CHANGES IN CAPITALIZATION, ETC.

             (a)   In the event of any change in Issuer Common Stock by reason
of a stock dividend, stock split, split- up, recapitalization, combination,
exchange of shares or similar transaction, the type and number of shares or
securities subject to the Option, and the Purchase Price therefor, shall be
adjusted appropriately, and proper provision shall be made in the agreements
governing such transaction so that Holder shall receive, upon exercise of the
Option, the number and class of shares or other securities or property that
Holder would have received in respect of Issuer Common Stock if the Option had
been exercised immediately prior to such event, or the record date therefor, as
applicable.  If any additional shares of Issuer Common Stock are issued after
the date of this Agreement (other than pursuant to an event described in the
first sentence of this Section 7(a) or pursuant to this Option), the number of
shares of Issuer Common Stock subject to the Option shall be adjusted so that,
after such issuance, it, together with any shares of Issuer Common Stock
previously issued pursuant hereto, equals 19.9% of the number of shares of
Issuer Common Stock then issued and outstanding, without giving effect to any
shares subject to or issued pursuant to the Option.

             (b)   In the event that Issuer shall enter in an agreement: (i) to
consolidate with or merge into any person, other than Grantee or one of its
Subsidiaries, and shall not be the continuing or surviving corporation of such
consolidation or merger; (ii) to permit any person, other than Grantee or one
of its Subsidiaries, to merge into Issuer and Issuer shall be the continuing or
surviving corporation, but, in connection with such merger, the then
outstanding shares of Issuer Common Stock shall be changed into or exchanged
for stock or other securities of Issuer or any other person or cash or any
other property or the outstanding shares of Issuer Common Stock immediately
prior to such merger shall after such merger represent less than 50% of the
outstanding shares and share equivalents of the merged company; or (iii) to
sell or otherwise transfer all or substantially all of its Assets to any
person, other than Grantee or one of





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its Subsidiaries, then, and in each such case, the agreement governing such
transaction shall make proper provisions so that the Option shall, upon the
consummation of any such transaction and upon the terms and conditions set
forth herein, be converted into, or exchanged for, an option (the "Substitute
Option"), at the election of Grantee, of either (x) the Acquiring Corporation
(as defined below), (y) any person that controls the Acquiring Corporation, or
(z) in the case of a merger described in clause (ii), the Issuer (in each case,
such person being referred to as the "Substitute Option Issuer").

             (c)   The Substitute Option shall have the same terms as the
Option, provided that, if the terms of the Substitute Option cannot, for legal
reasons, be the same as the Option, such terms shall be as similar as possible
and in no event less advantageous to Grantee.  The Substitute Option Issuer
shall also enter into an agreement with the then-holder or holders of the
Substitute Option in substantially the same form as this Agreement, which shall
be applicable to the Substitute Option.

             (d)   The Substitute Option shall be exercisable for such number
of shares of the Substitute Common Stock (as hereinafter defined) as is equal
to the Assigned Value (as hereinafter defined) multiplied by the number of
shares of the Issuer Common Stock for which the Option was theretofore
exercisable, divided by the Average Price (as hereinafter defined).  The
exercise price of the Substitute Option per share of the Substitute Common
Stock (the "Substitute Purchase Price") shall then be equal to the Purchase
Price multiplied by a fraction in which the numerator is the number of shares
of the Issuer Common Stock for which the Option was theretofore exercisable and
the denominator is the number of shares for which the Substitute Option is
exercisable.

             (e)   The following terms have the meanings indicated:

                   (i)    "Acquiring Corporation" shall mean (x) the continuing
      or surviving corporation of a consolidation or merger with Issuer (if
      other than Issuer), (y) Issuer in a merger in which Issuer is the
      continuing or surviving person, and (z) the transferee of all or any
      substantial part of the Issuer's assets (or the assets of its
      Subsidiaries).

                   (ii)   "Substitute Common Stock" shall mean the common stock
      issued by the Substitute Option Issuer upon exercise of the Substitute
      Option.

                   (iii)  "Assigned Value" shall mean the highest of (x) the
      price per share of the Issuer Common Stock at which a Tender Offer or
      Exchange Offer therefor has been made by any person (other than Grantee),
      (y) the price per share of the Issuer Common Stock to be paid by any
      person (other than the Grantee) pursuant to an agreement with Issuer, and
      (z) the highest closing sales price per share of Issuer Common Stock
      quoted on the Nasdaq National Market (or if Issuer Common Stock is not
      quoted on the Nasdaq National Market, the highest bid price per share on
      any day as quoted on the principal trading market or securities exchange
      on which such shares are traded as reported by a recognized source chosen
      by Grantee) within the six-month period immediately preceding the
      agreement; provided, that in the event of a sale of less than all of
      Issuer's assets, the Assigned Value





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      shall be the sum of the price paid in such sale for such assets and the
      current market value of the remaining assets of Issuer as determined by a
      nationally recognized investment banking firm selected by Grantee (or by
      a majority in interest of the Grantees if there shall be more than one
      Grantee (a "Grantee Majority")), divided by the number of shares of the
      Issuer Common Stock outstanding at the time of such sale.  In the event
      that an exchange offer is made for the Issuer Common Stock or an
      agreement is entered into for a merger or consolidation involving
      consideration other than cash, the value of the securities or other
      property issuable or deliverable in exchange for the Issuer Common Stock
      shall be determined by a nationally recognized investment banking firm
      mutually selected by Grantee and Issuer (or if applicable, Acquiring
      Corporation), provided that if a mutual selection cannot be made as to
      such investment banking firm, it shall be selected by Grantee.  (If there
      shall be more than one Grantee, any such selection shall be made by a
      Grantee Majority.)

                   (iv)   "Average Price" shall mean the average closing price
      of a share of the Substitute Common Stock for the one year immediately
      preceding the consolidation, merger or sale in question, but in no event
      higher than the closing price of the shares of the Substitute Common
      Stock on the day preceding such consolidation, merger or sale; provided
      that if Issuer is the issuer of the Substitute Option, the Average Price
      shall be computed with respect to a share of common stock issued by
      Issuer, the person merging into Issuer or by any company which controls
      or is controlled by such merger person, as Grantee may elect.

             (f)   In no event pursuant to any of the foregoing paragraphs
shall the Substitute Option be exercisable for more than 19.9% of the aggregate
of the shares of the Substitute Common Stock outstanding prior to exercise of
the Substitute Option.  In the event that the Substitute Option would be
exercisable for more than 19.9% of the aggregate of the shares of Substitute
Common Stock but for this clause (f), the Substitute Option Issuer shall make a
cash payment to Grantee equal to the excess of (i) the value of the Substitute
Option without giving effect to the limitation in this clause (f) over (ii) the
value of the Substitute Option after giving effect to the limitation in this
clause (f).  This difference in value shall be determined by a nationally
recognized investment banking firm selected by Grantee (or a Grantee Majority).

             (g)   Issuer shall not enter into any transaction described in
subsection (b) of this Section 7 unless the Acquiring Corporation and any
person that controls the Acquiring Corporation assume in writing all the
obligations of Issuer hereunder and take all other actions that may be
necessary so that the provisions of this Section 7 are given full force and
effect (including, without limitation, any action that may be necessary so that
the shares of Substitute Common Stock are in no way distinguishable from or
have lesser economic value than other shares of common stock issued by the
Substitute Option Issuer).

             (h)   The provisions of Sections 8, 9, 10 and 11 shall apply, with
appropriate adjustments, to any securities for which the Option becomes
exercisable pursuant to this Section 7 and, as applicable, references in such
sections to "Issuer," "Option," "Purchase Price" and "Issuer Common Stock"
shall be deemed to be references to "Substitute Option Issuer," "Substitute
Option," "Substitute Purchase Price" and "Substitute Common Stock,"
respectively.





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      8.     REPURCHASE AT THE OPTION OF HOLDER.

             (a)   Subject to the last sentence of Section 3(a), at the request
of Holder at any time commencing upon the first occurrence of a Repurchase
Event (as defined in Section 8(d)) and ending 12 months immediately thereafter,
Issuer shall repurchase from Holder the Option and all shares of Issuer Common
Stock purchased by Holder pursuant hereto with respect to which Holder then has
beneficial ownership.  The date on which Holder exercises its rights under this
Section 8 is referred to as the "Request Date."  Such repurchase shall be at an
aggregate price (the "Section 8 Repurchase Consideration") equal to the sum of:

                   (i)    the aggregate Purchase Price paid by Holder for any
      shares of Issuer Common Stock acquired by Holder pursuant to the Option
      with respect to which Holder then has beneficial ownership;

                   (ii)   the excess, if any, of (x) the Applicable Price (as
      defined below) for each share of Issuer Common Stock over (y) the
      Purchase Price (subject to adjustment pursuant to Section 7), multiplied
      by the number of shares of Issuer Common Stock with respect to which the
      Option has not been exercised; and

                   (iii)  the excess, if any, of the Applicable Price over the
      Purchase Price (subject to adjustment pursuant to Section 7) paid (or, in
      the case of Option Shares with respect to which the Option has been
      exercised but the Closing Date has not occurred, payable) by Holder for
      each share of Issuer Common Stock with respect to which the Option has
      been exercised and with respect to which Holder then has beneficial
      ownership, multiplied by the number of such shares.

             (b)   If Holder exercises its rights under this Section 8, Issuer
shall, within ten business days after the Request Date, pay the Section 8
Repurchase Consideration to Holder in immediately available funds, and
contemporaneously with such payment Holder shall surrender to Issuer the Option
and the certificates evidencing the shares of Issuer Common Stock purchased
thereunder with respect to which Holder then has beneficial ownership, and
Holder shall warrant that it has sole record and beneficial ownership of such
shares and that the same are then free and clear of all liens, claims, charges
and encumbrances of any kind whatsoever.  Notwithstanding the foregoing, to the
extent that prior notification to or Consent of any governmental or regulatory
agency or authority is required in connection with the payment of all or any
portion of the Section 8 Repurchase Consideration, Holder shall have the
ongoing option to revoke its request for repurchase pursuant to Section 8, in
whole or in part, or to require that Issuer deliver from time to time that
portion of the Section 8 Repurchase Consideration that it is not then so
prohibited from paying and promptly file the required notice or application for
Consent and expeditiously process the same (and each party shall cooperate with
the other in the filing of any such notice or application and the obtaining of
any such Consent).  If any governmental or regulatory agency or authority
disapproves of any part of Issuer's proposed repurchase pursuant to this
Section 8,





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<PAGE>   10

Issuer shall promptly give notice of such fact to Holder.  If any governmental
or regulatory agency or authority prohibits the repurchase in part but not in
whole, then Holder shall have the right (i) to revoke the repurchase request or
(ii) to the extent permitted by such agency or authority, determine whether the
repurchase should apply to the Option and/or Option Shares and to what extent
to each, and Holder shall thereupon have the right to exercise the Option as to
the number of Option Shares for which the Option was exercisable at the Request
Date less the sum of the number of shares covered by the Option in respect of
which payment has been made pursuant to Section 8(a)(ii) and the number of
shares covered by the portion of the Option (if any) that has been repurchased.
Holder shall notify Issuer of its determination under the preceding sentence
within five business days of receipt of notice of disapproval of the
repurchase.

                   Notwithstanding anything herein to the contrary, all of
Holder's rights under this Section 8 shall terminate on the date of termination
of this Option pursuant to Section 3(a).

             (c)   For purposes of this Agreement, the "Applicable Price" means
the highest of (i) the highest price per share of Issuer Common Stock paid for
any such share by the person or groups described in Section 8(d)(i), (ii) the
price per share of Issuer Common Stock received by holders of Issuer Common
Stock in connection with any merger or other business combination transaction
described in Section 7(b)(i), 7(b)(ii) or 7(b)(iii), or (iii) the highest
closing sales price per share of Issuer Common Stock quoted on the Nasdaq
National Market (or if Issuer Common Stock is not quoted on the Nasdaq National
Market, the highest bid price per share as quoted on the principal trading
market or securities exchange on which such shares are traded as reported by a
recognized source chosen by Holder) during the 60 business days preceding the
Request Date; provided, however, that in the event of a sale of less than all
of Issuer's Assets, the Applicable Price shall be the sum of the price paid in
such sale for such assets and the current market value of the remaining assets
of Issuer as determined by an independent nationally recognized investment
banking firm selected by Holder and reasonably acceptable to Issuer (which
determination shall be conclusive for all purposes of this Agreement), divided
by the number of shares of the Issuer Common Stock outstanding at the time of
such sale.  If the consideration to be offered, paid or received pursuant to
either of the foregoing clauses (i) or (ii) shall be other than in cash, the
value of such consideration shall be determined in good faith by an independent
nationally recognized investment banking firm selected by Holder and reasonably
acceptable to Issuer, which determination shall be conclusive for all purposes
of this Agreement.

             (d)   As used herein, "Repurchase Event" shall occur if (i) any
person (other than Grantee or any Subsidiary of Grantee) shall have acquired
actual ownership or control, or any "group" (as such term is defined under the
1934 Act) shall have been formed which shall have acquired actual ownership or
control, of 50% or more of the then-outstanding shares of Issuer Common Stock,
or (ii) any of the transactions described in Section 7(b)(i), 7(b)(ii) or
7(b)(iii) shall be consummated.

             (e)   In connection with the application of the provisions of this
Section 8, Grantee acknowledges (i) that Issuer's ability to fund the Section 8
Repurchase Consideration in accordance with the provisions of this Section 8
may be dependent upon the payment by Issuer's Subsidiaries of a capital
distribution or distributions ("Capital Distribution") to Issuer and that any





                                     - 10 -

<PAGE>   11

such Capital Distribution will be subject to the prior approval of the Federal
Reserve Board and the principal federal and state regulatory agencies having
jurisdiction over Issuer's Subsidiary banks, and (ii) that, unless there has
been an agreement of the type described in Section 7(b), Issuer's obligations
under this Section 8 do not impose on Issuer an obligation to otherwise finance
the payment of the Section 8 Repurchase Consideration through the incurrence of
indebtedness or the issuance of capital instruments or securities by Issuer in
either case sufficient in amount to satisfy the payment of the Section 8
Repurchase Consideration.  Accordingly, Issuer shall not be deemed to be in
breach of this Section 8 if, after making its best efforts to obtain regulatory
authorization for a Capital Distribution required to pay the Section 8
Repurchase Consideration, it is unable to do so.

      9.     REGISTRATION RIGHTS.

             (a)   Following termination of the Merger Agreement (provided that
the Option shall not have terminated), Issuer shall, subject to the conditions
of subparagraph (c) below, if requested by any Holder, including Grantee and
any permitted transferee ("Selling Holder"), as expeditiously as possible
prepare and file a registration statement under the Securities Laws if
necessary in order to permit the sale or other disposition of any or all shares
of Issuer Common Stock or other securities that have been acquired by or are
issuable to Selling Holder upon exercise of the Option in accordance with the
intended method of sale or other disposition stated by Holder in such request
(it being understood and agreed that any such sale or other disposition shall
be effected on a widely distributed basis so that, upon consummation thereof,
no purchaser or transferee shall beneficially own more than 2% of the shares of
Issuer Common Stock then outstanding), including, without limitation, a "shelf"
registration statement under Rule 415 under the Securities Act or any successor
provision, and Issuer shall use its best efforts to qualify such shares or
other securities for sale under any applicable state securities laws.  Each
such Holder shall provide all information reasonably requested by Issuer for
inclusion in any registration statement to be filed hereunder.

             (b)   If Issuer at any time after the exercise of the Option
proposes to register any shares of Issuer Common Stock under the Securities
Laws in connection with an underwritten public offering of such Issuer Common
Stock, Issuer will promptly give written notice to Holder of its intention to
do so and, upon the written request of Holder given within 30 days after
receipt of any such notice (which request shall specify the number of shares of
Issuer Common Stock intended to be included in such underwritten public
offering by Selling Holder), Issuer will cause all such shares, the holders of
which shall have requested participation in such registration, to be so
registered and included in such underwritten public offering; provided, that
Issuer may elect to not cause any such shares to be so registered (i) if the
underwriters in good faith object for valid business reasons, or (ii) in the
case of a registration solely to implement a dividend reinvestment or similar
plan, an employee benefit plan or a registration filed on Form S-4 or any
successor form, or a registration filed on a form which does not permit
registrations of resales; provided, further, that such election pursuant to
clause (i) may only be made once.  If some but not all the shares of Issuer
Common Stock, with respect to which Issuer shall have received requests for
registration pursuant to this subparagraph (b), shall be excluded from such
registration, Issuer shall make appropriate allocation of shares to be
registered among Selling Holders and any other





                                     - 11 -

<PAGE>   12

person (other than Issuer or any person exercising demand registration rights
in connection with such registration) who or which is permitted to register
their shares of Issuer Common Stock in connection with such registration pro
rata in the proportion that the number of shares requested to be registered by
each Selling Holder bears to the total number of shares requested to be
registered by all persons then desiring to have Issuer Common Stock registered
for sale.

             (c)   Issuer shall use all reasonable efforts to cause the
registration statement referred to in subparagraph (a) above to become
effective and to obtain all consents or waivers of other parties which are
required therefor and to keep such registration statement effective, provided,
that Issuer may delay any registration of Option Shares required pursuant to
subparagraph (a) above for a period not exceeding 90 days provided Issuer shall
in good faith determine that any such registration would adversely affect an
offering or contemplated offering of other securities by Issuer, and Issuer
shall not be required to register Option Shares under the Securities Laws
pursuant to subparagraph (a) above:

                   (i)    prior to the earliest of (A) termination of the
      Merger Agreement pursuant to Section 10.1 thereof, (B) failure to obtain
      the requisite shareholder approval pursuant to Section 9.1(a) of the
      Merger Agreement, and (C) a Purchase Event or a Preliminary Purchase
      Event;

                   (ii)   more than once;

                   (iii)  within 90 days after the effective date of a
      registration referred to in subparagraph (b) above pursuant to which the
      Selling Holders concerned were afforded the opportunity to register such
      shares under the Securities Laws and such shares were registered as
      requested; and

                   (iv)   unless a request therefor is made to Issuer by
      Selling Holders holding at least 25% or more of the aggregate number of
      Option Shares then outstanding.

                   In addition to the foregoing, Issuer shall not be required
to maintain the effectiveness of any registration statement after the
expiration of 120 days from the effective date of such registration statement.
Issuer shall use all reasonable efforts to make any filings, and take all
steps, under all applicable state securities laws to the extent necessary to
permit the sale or other disposition of the Option Shares so registered in
accordance with the intended method of distribution for such shares, provided,
that Issuer shall not be required to consent to general jurisdiction or qualify
to do business in any state where it is not otherwise required to so consent to
such jurisdiction or to so qualify to do business.

             (d)   Except where applicable state law prohibits such payments,
Issuer will pay all expenses (including without limitation registration fees,
qualification fees, blue sky fees and expenses (including the fees and expenses
of Issuer's counsel), accounting expenses, printing expenses, expenses of
underwriters, excluding discounts and commissions but including liability
insurance if Issuer so desires or the underwriters so require, and the
reasonable fees and expenses of any necessary special experts) in connection
with each registration pursuant to subparagraph





                                     - 12 -

<PAGE>   13

(a) or (b) above (including the related offerings and sales by Selling Holders)
and all other qualifications, notifications or exemptions pursuant to
subparagraph (a) or (b) above.  Underwriting discounts and commissions relating
to Option Shares and any other expenses incurred by such Selling Holders in
connection with any such registration (including expenses of Selling Holders'
counsel) shall be borne by such Selling Holders.

             (e)   In connection with any registration under subparagraph (a)
or (b) above Issuer hereby indemnifies the Selling Holders, and each
underwriter thereof, including each person, if any, who controls such holder or
underwriter within the meaning of Section 15 of the Securities Act, against all
expenses, losses, claims, damages and liabilities caused by any untrue
statement of a material fact contained in any registration statement or
prospectus or notification or offering circular (including any amendments or
supplements thereto) or any preliminary prospectus, or caused by any omission
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading, except insofar as such expenses,
losses, claims, damages or liabilities of such indemnified party are caused by
any untrue statement or alleged untrue statement that was included by Issuer in
any such registration statement or prospectus or notification or offering
circular (including any amendments or supplements thereto) in reliance upon and
in conformity with, information furnished in writing to Issuer by such
indemnified party expressly for use therein, and Issuer and each officer,
director and controlling person of Issuer shall be indemnified by such Selling
Holder, or by such underwriter, as the case may be, for all such expenses,
losses, claims, damages and liabilities caused by any untrue, or alleged
untrue, statement, that was included by Issuer in any such registration
statement or prospectus or notification or offering circular (including any
amendments or supplements thereto) in reliance upon, and in conformity with,
information furnished in writing to Issuer by such holder or such underwriter,
as the case may be, expressly for such use.

                   Promptly upon receipt by a party indemnified under this
subparagraph (e) of notice of the commencement of any action against such
indemnified party in respect of which indemnity or reimbursement may be sought
against any indemnifying party under this subparagraph (e), such indemnified
party shall notify the indemnifying party in writing of the commencement of
such action, but the failure so to notify the indemnifying party shall not
relieve it of any liability which it may otherwise have to any indemnified
party under this subparagraph (e).  In case notice of commencement of any such
action shall be given to the indemnifying party as above provided, the
indemnifying party shall be entitled to participate in and, to the extent it
may wish, jointly with any other indemnifying party similarly notified, to
assume the defense of such action at its own expense, with counsel chosen by it
and satisfactory to such indemnified party.  The indemnified party shall have
the right to employ separate counsel in any such action and participate in the
defense thereof, but the fees and expenses of such counsel (other than
reasonable costs of investigation) shall be paid by the indemnified party
unless (i) the indemnifying party either agrees to pay the same, (ii) the
indemnifying party falls to assume the defense of such action with counsel
satisfactory to the indemnified party, or (iii) the indemnified party has been
advised by counsel that one or more legal defenses may be available to the
indemnifying party that may be contrary to the interest of the indemnified
party, in which case the indemnifying party shall be entitled to assume the
defense of such action notwithstanding its obligation to bear fees and





                                     - 13 -

<PAGE>   14

expenses of such counsel.  No indemnifying party shall be liable for any
settlement entered into without its consent, which consent may not be
unreasonably withheld.

                   If the indemnification provided for in this subparagraph (e)
is unavailable to a party otherwise entitled to be indemnified in respect of
any expenses, losses, claims, damages or liabilities referred to herein, then
the indemnifying party, in lieu of indemnifying such party otherwise entitled
to be indemnified, shall contribute to the amount paid or payable by such party
to be indemnified as a result of such expenses, losses, claims, damages or
liabilities in such proportion as is appropriate to reflect the relative
benefits received by Issuer, all Selling Holders and the underwriters from the
offering of the securities and also the relative fault of Issuer, all Selling
Holders and the underwriters in connection with the statements or omissions
which resulted in such expenses, losses, claims, damages or liabilities, as
well as any other relevant equitable considerations.  The amount paid or
payable by a party as a result of the expenses, losses, claims, damages and
liabilities referred to above shall be deemed to include any legal or other
fees or expenses reasonably incurred by such party in connection with
investigating or defending any action or claim; provided, that in no case shall
any Selling Holder be responsible, in the aggregate, for any amount in excess
of the net offering proceeds attributable to its Option Shares included in the
offering.  No person guilty of fraudulent misrepresentation (within the meaning
of Section 11(f) of the Securities Act) shall be entitled to contribution from
any person who was not guilty of such fraudulent misrepresentation.  Any
obligation by any holder to indemnify shall be several and not joint with other
holders.

                   In connection with any registration pursuant to subparagraph
(a) or (b) above, Issuer and each Selling Holder (other than Grantee) shall
enter into an agreement containing the indemnification provisions of this
subparagraph (e).

             (f)   Issuer shall comply with all reporting requirements and will
do all such other things as may be necessary to permit the expeditious sale at
any time of any Option Shares by Holder in accordance with and to the extent
permitted by any rule or regulation promulgated by the SEC from time to time,
including, without limitation, Rules 144 and 144A.

             (g)   Issuer will pay all stamp taxes in connection with the
issuance and the sale of the Option Shares and in connection with the exercise
of the Option, and will save Holder harmless, without limitation as to time,
against any and all liabilities, with respect to all such taxes.

      10.    QUOTATION; LISTING.  If Issuer Common Stock or any other
securities to be acquired upon exercise of the Option are then authorized for
quotation or trading or listing on the Nasdaq National Market or any other
securities exchange or any automated quotations system maintained by a
self-regulatory organization, Issuer, upon the request of Holder, will promptly
file an application, if required, to authorize for quotation or trading or
listing the shares of Issuer Common Stock or other securities to be acquired
upon exercise of the Option on the Nasdaq National Market or any other
securities exchange or any automated quotations system maintained by a
self-regulatory organization and will use its best efforts to obtain approval,
if required, of such quotation or listing as soon as practicable.





                                     - 14 -

<PAGE>   15

      11.    DIVISION OF OPTION.  This Agreement (and the Option granted
hereby) are exchangeable, without expense, at the option of Holder, upon
presentation and surrender of this Agreement at the principal office of Issuer
for other Agreements providing for Options of different denominations entitling
the holder thereof to purchase in the aggregate the same number of shares of
Issuer Common Stock purchasable hereunder.  The terms "Agreement" and "Option"
as used herein include any other Agreements and related Options for which this
Agreement (and the Option granted hereby) may be exchanged.  Upon receipt by
Issuer of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Agreement, and (in the case of loss, theft or
destruction) of reasonably satisfactory indemnification, and upon surrender and
cancellation of this Agreement, if mutilated, Issuer will execute and deliver a
new Agreement of like tenor and date.  Any such new Agreement executed and
delivered shall constitute an additional contractual obligation on the part of
Issuer, whether or not the Agreement so lost, stolen, destroyed or mutilated
shall at any time be enforceable by anyone.

      12.    MISCELLANEOUS.

             (A)   EXPENSES.  Except as otherwise provided in Section 9, each
of the parties hereto shall bear and pay all costs and expenses incurred by it
or on its behalf in connection with the transactions contemplated hereunder,
including fees and expenses of its own financial consultants, investment
bankers, accountants and counsel.

             (B)   WAIVER AND AMENDMENT.  Any provision of this Agreement may
be waived at any time by the party that is entitled to the benefits of such
provision.  This Agreement may not be modified, amended, altered or
supplemented except upon the execution and delivery of a written agreement
executed by the parties hereto.

             (C)   ENTIRE AGREEMENT; NO THIRD-PARTY BENEFICIARY; SEVERABILITY.
This Agreement, together with the Merger Agreement and the other documents and
instruments referred to herein and therein, between Grantee and Issuer (a)
constitutes the entire agreement and supersedes all prior agreements and
understandings, both written and oral, between the parties with respect to the
subject matter hereof and (b) is not intended to confer upon any person other
than the parties hereto (other than any transferees of the Option Shares or any
permitted transferee of this Agreement pursuant to Section 12(h) and other than
as provided in the Merger Agreement) any rights or remedies hereunder.  If any
term, provision, covenant or restriction of this Agreement is held by a court
of competent jurisdiction or a federal or state governmental or regulatory
agency or authority to be invalid, void or unenforceable, the remainder of the
terms, provisions, covenants and restrictions of this Agreement shall remain in
full force and effect and shall in no way be affected, impaired or invalidated.
If for any reason such court or regulatory agency determines that the Option
does not permit Holder to acquire, or does not require Issuer to repurchase,
the full number of shares of Issuer Common Stock as provided in Sections 3 and
8 (as adjusted pursuant to Section 7), it is the express intention of Issuer to
allow Holder to acquire or to require Issuer to repurchase such lesser number
of shares as may be permissible without any amendment or modification hereof.





                                     - 15 -

<PAGE>   16

             (D)   GOVERNING LAW.  This Agreement shall be governed and
construed in accordance with the laws of the State of Tennessee without regard
to any applicable conflicts of law rules.

             (E)   DESCRIPTIVE HEADINGS.  The descriptive headings contained
herein are for convenience of reference only and shall not affect in any way
the meaning or interpretation of this Agreement.

             (F)   NOTICES.  All notices and other communications hereunder
shall be in writing and shall be deemed given if delivered personally,
telecopied (with confirmation) or mailed by registered or certified mail
(return receipt requested) to the parties at the addresses set forth in the
Merger Agreement(or at such other address for a party as shall be specified by
like notice).

             (G)   COUNTERPARTS.  This Agreement and any amendments hereto may
be executed in two counterparts, each of which shall be considered one and the
same agreement and shall become effective when both counterparts have been
signed, it being understood that both parties need not sign the same
counterpart.

             (H)   ASSIGNMENT.  Neither this Agreement nor any of the rights,
interests or obligations hereunder or under the Option shall be assigned by any
of the parties hereto (whether by operation of law or otherwise) without the
prior written consent of the other party, except that Grantee may assign this
Agreement to a wholly owned Subsidiary of Grantee and Grantee may assign its
rights hereunder in whole or in part after the occurrence of a Purchase Event.
Subject to the preceding sentence, this Agreement shall be binding upon, inure
to the benefit of and be enforceable by the parties and their respective
successors and assigns.

             (I)   FURTHER ASSURANCES.  In the event of any exercise of the
Option by Holder, Issuer and Holder shall execute and deliver all other
documents and instruments and take all other action that may be reasonably
necessary in order to consummate the transactions provided for by such
exercise.

             (J)   SPECIFIC PERFORMANCE.  The parties hereto agree that this
Agreement may be enforced by either party through specific performance,
injunctive relief and other equitable relief.  Both parties further agree to
waive any requirement for the securing or posting of any bond in connection
with the obtaining of any such equitable relief and that this provision is
without prejudice to any other rights that the parties hereto may have for any
failure to perform this Agreement.





                                     - 16 -

<PAGE>   17

      IN WITNESS WHEREOF, Issuer and Grantee have caused this Stock Option
Agreement to be signed by their respective officers thereunto duly authorized,
all as of the day and year first written above.

<TABLE>
<S>                                                <C>
ATTEST:                                            MAGNA BANCORP, INC.


By:  /s/ H. A. Moore, III                          By:  /s/ Robert S. Duncan                          
     ------------------------------------------    ---------------------------------------------------
     H. A. Moore, III                                   Robert S. Duncan
     Secretary                                          Chairman of the Board and
                                                            Chief Executive Officer


[CORPORATE SEAL]


ATTEST:                                            UNION PLANTERS CORPORATION


By:  /s/ E. J. House, Jr.                          By:  /s/ Benjamin W. Rawlins, Jr.                  
     ------------------------------------------         ----------------------------------------------
     E.J. House, Jr.                                    Benjamin W. Rawlins, Jr.
     Secretary                                          Chairman and Chief Executive Officer



[CORPORATE SEAL]
</TABLE>





                                     - 17 -