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                                                                 Exhibit 10.5.3



                            FIRST AMENDMENT OF LEASE

         This First Amendment of Lease ("Amendment") is made and entered into as
of the 1st day of of March, 1999 by and between MARTIN P. HULL, MIEKE DANKERS,
DENNIS W. ROYER and CHRISTINE J. ROYER, tenants in common, each hereinafter
referred to as "Lessor" and DELTAGEN, a Delaware corporation ("Lessee").

                                    RECITALS

         A. Lessor and Lessee entered into a lease dated January 25, 1997
("Lease"), for the lease of the building at 1031 Bing Street, San Carlos, San
Mateo County, California ("Premises").

         B. Lessor and Lessee now desire to amend the terms of the Lease to
provide for an extension of the Lease Term.

         NOW, THEREFORE, in cosideration of the foregoing, and other good and
valuable consideration, the receipt of which is hereby acknowledged, Lessor and
Lessee agree as follows:

         1. Unless otherwise expressly provided herein, all terms which are
given a special definition by the Lease, that are used herein, are intended to
be used with the definition given to them in the Lease. The provisions of the
Lease shall remain in full force and effect except as specifically amended
hereby: In the event of any inconsistency between the Lease and this Amendment,
the terms of this Amendment shall prevail.

         2. Paragraph 1.3 is amended to extend the Lease Expiration Date by four
(4) years to the date of February 29, 2004.

         3. Paragraph 1.5 is amended to provide for the payment of the following
sums of Base Rent:

            Commencing on March 1, 1999, and continuing through the month of
February, 2004, the monthly Base Rent shall be $13,260.00.

         4. Paragraph 7.4 is amended as follows: Notwithstanding anything else
contained in the Lease to the contrary, Lessee Owned Alterations and Utility
Installations may be retained and removed from the Premises by the Lessee, at
the termination of the Lease term. Any items not removed shall become the
property of Lessor. Upon surrender of the Premises, at the Lease termination,
Lessee shall not be responsible for removal of approved Lessee Owned Alterations
or Utility Installations, nor the restoration of the Premises to its original
condition, prior to the commencement of the Lease. Nevertheless, any damage
caused by the removal of Lessee's property from the Premises shall be repaired
by Lessee. Upon surrender of the Premises, the Premises shall be clean and free
of debris and in good operating order, condition and state of repair, ordinary
wear and tear excepted.

         5. Paragraph 50(d) is replaced as follows: "Lessor and Lessee agree
that Lessor shall have no obligation to maintain HVAC units, except for the HVAC
units which were installed in the premises by January 25, 1997. However, with
respect to those units, Lessee shall bear the first $4,800 of maintenance or
repair cost each year."

         6. Paragraph 51 of the Lease is deleted in its entirety.

         7. Paragraph 52 of the Lease is deleted in its entirety.

         8. Paragraph 53 of the Lease is deleted in its entirety.

         9. Lessor agrees to pay for any and all brokerage services or fees
incurred by Lessor to obtain this Lease extension, if any, and in the event
Lessee exercises the option set forth below, for the Lease extension
resulting from the exercise of the option. Lessee shall not be obligted to
pay Lessor's real


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estate brokerage fees. Lessor and Lessee each agree to indemnify, defend and
hold the other party harmless from and against any and all liability, damages
and costs (including attorneys' fees) incurred by the other as a result of a
claim made by the other party's real estate broker.

         10.      Provided Lessee is not in material default under any of the
terms, covenants or conditions of this Lease, and subject to the terms and
conditions set forth herein, Lessee is herby granted the option to extend this
Lease for a period of five (5) years:

         a.       Lessee shall notify Lessor in writing of Lessee's exercise of
                  the option on or before December 1, 2003.

         b.       The extended term of this Lease shall commence on March 1,
                  2004 and shall end on February 28, 2009 ("First Extended
                  Term").

         c.       The monthly Base rent shall continue to be the monthly sum of
                  $13,260.00 throughout the First Extended term.

         11.      Except as herein modified and amended, the Lease shall remain
in full force and effect.

         IN WITNESS WHEREOF, the parties have signed this First Amendment of
Lease, which, for reference purposes, shall be deemed to have been dated as of
March 1, 1999.


Lessor:                                        Lessee:


  /s/ Martin P. Hull                           DELTAGEN, a Delaware corporation
------------------------------------
Martin P. Hull


  /s/ Mieke Dankers                     By:      /s/ William Matthews
------------------------------------           --------------------------------
Mieke Dankers                                  Its Chief Executive Officer


  /s/ Dennis W. Royers
-----------------------------------
Dennis W. Royers


  /s/ Christine J. Royers
-----------------------------------
Christine J. Royers