bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of peroxidases in cucumber hypocotyls by wounding and fungal infection
Authors: Svalheim Øystein , Robertsen Børre
Published: May 2006

The induction of peroxidases (EC 1.11.1.7) during elicitation of lignification by α‐1,4‐linked oligogalacturonides in cucumber hypocotyl segments (Cucumis sativus L. cv, Wisconsin SMR 58) was investigated. The wounding associated with the preparation of hypocotyl segments induced a 19‐fold increase in peroxidase activity during the following 72 h. The increase was partially due to an increase in activity of a constitutive peroxidase with a pI of 8.9 and partially due to the expression of new peroxidase isozymes with pIs of 3.8, 5.4, 6.2, 9.1 and 9.4. The oligogalacturonides did not induce any peroxidase activity in addition to the wound‐induced activity. These results suggest that either the constitutive peroxidase isozyme (pI 8.9) of intact hypocotyls or some of the wound‐induced peroxidases are involved in the oligogalacturonide‐induced lignification.

Induction of the peroxidases by wounding was inhibited by cycloheximide. This indicates that they accumulate as a result of de novo protein synthesis. Actinomycin D caused only a modest inhibition of the wound‐induction peroxidases, indicating that the process is regulated at the level of translation.

Peroxidase activity increased more rapidly in resistant than in susceptible cucumber hypocotyls after inoculation with the pathogen Cladosporium cucumerinum Ellis & Arthur. The pattern of isozymes which was induced by fungal infection of resistant hypocotyls was similar to the pattern of isozymes induced by wounding. This suggests that similar induction mechanisms may be involved in the two processes.
Adventitious rooting in hypocotyls of sunflower (Helianthus annuus) seedlings. III. The role of ethylene
Authors: Liu Jinhao , Mukherjee Llabant , Reid David M.
Published: May 2006

While ethylene is suspected to be one of the many factors that play a role in rooting, some studies have found that ethylene can promote rooting, while others show it to inhibit this process or to have no effect. Using seedlings of sunflower (Helianthus annuus L. cv. Dahlgren 131) we carried out observations on the rates of ethylene production and the levels of the ethylene precursor, 1‐aminocyclopropane‐l‐car‐boxylic acid (ACC), and ACC conjugate, l‐(malonylamino)cyclopropane‐l‐car‐boxylic acid (MACC), during the process of root initiation. The changes in these substances in the base of the hypocotyls (the portion that produces roots) were compared to the changes that occurred in the top of the hypocotyls (non‐rooting portion). We also supplied a number of presumptive inhibitors of ethylene biosynthesis and inhibitors of ethylene action for short periods during the early and critical stages of root formation. Their effects on ethylene action, synthesis and rooting were examined. We conclude that the wound‐induced increase in ethylene, seen within 3 h of production of the cuttings, is a key stimulatory factor in the formation of root primordia. When this increase in ethylene is localized in the lower portion of the hypocotyl, there is a promotion of rooting. On the other hand, higher concentrations in the top of the hypocotyls (as compared to the bottom) may inhibit rooting.
Influence of extraction solvent (buffer, methanol, acetone) and time on the quantification of indoIe‐3‐acetic acid in plants
Authors: Sundberg Björn
Published: May 2006

The effect of extraction solvent and time on the measured indole‐3‐acetic acid (IAA) level was investigated in plant materials having different contents of lAA‐conjugates, Tissues from pine (Pinus sylvestris L.). tobacco (Nicotiana tabacum L.), and maize (Zea mays L.) were extracted for 1–9 h with Na‐phosphate buffer (pH 7.5). 80% methanol and 70% acetone. IAA was measured by combined gas chromatography‐selected ion minitoring‐mass spectromctry (GC‐SIM‐MS) with [13C6]‐IAA as an internal standard.

Extraction of maize seedlings with buffer gave a higher estimate of free IAA than did extraction with methanol or acetone, which produced similar values. The increase in free IAA after buffer extraction was paralleled by a stoichiometric decrease in lAA‐ester conjugates, indicating that free IAA was formed during buffer extraction by hydrolysis of these conjugates, which are abundant in maize seedlings. The amount of hydrolysis during a 1‐h extraction period was estimated to be ca 3% of the total lAA‐ester pool. However, in the pine extraxylary tissues and tobacco in‐ternodes which lack a significant lAA‐ester pool, buffer extraction resulted in the same IAA estimate as extraction with the organic solvents, but produced a cleaner extract. For all the plant materials investigated, a 1‐h extraction period was sufficient for equilibrating the internal standard with the endogenous IAA pool.
Sieve element unloading: cellular pathway, mechanism and control
Authors: Patrick J. W.
Published: May 2006

The transport and distribution of phloem – mobile solutes is predominantly determined by transport processes located at the sink end of the source – transport – sink system. Transport across the sieve element boundary, sieve element unloading, is the first of a series of sink transport processes. Unloading of solutes from the sieve elements may follow an apo‐ or symplastic route. It is speculated that the unloading pathway is integrated with sink function and that apoplastic unloading is restricted to situations in which movement through the symplast is not compatible with sink function. These situations include axial transport and storage of osmotically active solutes against concentration and turgor gradients between the sieve elements and sink cells. Coupled with alteration in sink function, the cellular pathway of unloading can switch in stems and possibly other sinks. Experimental systems and approaches used to elucidate the mechanism of sieve element unloading are reviewed. Unloading fluxes to the apoplast can largely be accounted for by membrane diffusion in axial sinks. However, the higher fluxes in storage sinks suggests dependence on some form of facilitated transport. Proton sucrose symport is assessed to be a possible mechanism for facilitated efflux of solutes across the sieve element plasma membrane to the sink apoplast. Unloading through the symplast may occur by diffusion or mass flow. The latter mechanism serves to dissipate phloem water and hence prevent the potential elevation of sieve element turgor that would otherwise slow phloem import into the sink. The possibility of energised plasmodesmatal transport is raised. Sieve element unloading must be integrated with subsequent compartmentation and metabolism of the unloaded solute. Solute levels are an obvious basis for control of sieve element unloading, but are found to offer limited scope for a mass action mechanism. Apoplastic, cellular pathway, sieve element, solute transport, symplastic. Translated into a turgor signal, solute levels could regulate the rate of unloading, metabolism and compartmentation forming part of a turgor homeostat irrespective of the pathway of unloading.
Regulatory mechanisms of β‐glucan synthases in bacteria, fungi, and plants
Authors: Mullins J. Thomas
Published: May 2006

The evidence accumulated to date indicates that 1,3‐β‐glucan synthase (EC 2.3.1.12) and 1,4‐β‐glucan synthase (EC 2.4.1.12) are regulated by different effectors. Further that the same synthase has different effectors, depending upon its presence in green plants, fungi, and bacteria. Synthases from plants require divalent cations and β‐linked glucosides whereas fungal enzymes require neither cations nor β‐glucosides, but most require nucleoside triphosphates for activation. Two endogenous effectors have been characterized and shown to produce activation in vitro. One is 3′,5′‐cyclic diguanylic acid that is the activator of cellulose synthase in bacteria. The other is a β‐linked glucosyl dioleoyl diglyceride from mung bean, capable of activating synthases that produce both β‐(1–3) and β‐(1–4) products. The results of product analysis of the β‐linked glucoside activated reaction suggest that the synthesis of (1–3) and (1–4) glucosyl linkages may share a common enzyme in plants. All synthases utilize uridine 5′‐diphosphoglucose (UDPG) and are associated with the plasma membrane. Efforts to solubilize the synthases from cellular fractions enriched in plasma membranes have been generally successful. The purification of the soluble enzymes, however, remains a major obstacle to the full understanding of their regulation.
Effects of temperature and photoperiod on frost resistance of white clover (Trifolium repens) ecotypes
Authors: Junttila Olavi , Svenning Mette M. , Solheim Bjørn
Published: May 2006

Effects of photoperiod and temperature on frost resistance of seedling populations and clones of white clover (Trifolium repens L.) originating from various latitudes (58°48′–69°54′N) and altitudes (up to 1100 m above sea level) were studied in a phytotron. Low‐temperature‐induced cold acclimation in all populations was significantly stimulated by short photoperiod and low temperature. The highest levels of frost resistance were found in the northernmost seedling populations and in clones from northern coastal locations.
Inhibition and labeling of red beet uridine 5′diphospho‐glucose: (1,3)‐β‐glucan (callose) synthase by chemical modification with formaldehyde and uridine 5′diphospho‐pyridoxal
Authors: Mason Theresa L. , Read Stephen M. , Frost David J. , Wasserman Bruce P.
Published: May 2006

The effects of the lysine‐reactive chemical modification reagents, uridine 5’ diphospho (UDP)‐pyridoxal and formaldehyde (HCHO), on the activity of membrane‐bound and solubilized UDP‐Glc: (1,3)‐β‐D‐glucan synthase (callose synthase) from red beet (Beta vulgaris L.) storage tissue were compared. Exposure to micromolar levels of UDP‐pyridoxal, or millimolar levels of HCHO in the presence of NaCNBH3, resulted in complete enzyme inactivation. Conditions for inhibition of membrane‐bound enzyme activity by the two reagents were markedly similar; divalent cations were required for inactivation, and complete protection of activity was obtained with EDTA or EGTA. The substrate, UDP‐Glc, protected membrane‐bound callose synthase against inactivation by UDP‐pyridoxal or HCHO, but protected the solubilized enzyme only against inhibition by UDP‐pyridoxal, suggesting that the lysine residue modified by both these reagents is at the enzyme active site, and that the site is more open or has a certain conformational flexibility in the solubilized enzyme.

Potential UDP‐Glc‐binding polypeptides of callose synthase were identified by a two‐step labeling procedure. First, nonessential lysine residues were blocked by irreversible modification reaction with HCHO or UDP‐pyridoxal in the presence of UDP‐Glc to protect lysines at UDP‐Glc‐binding sites. In the second step, proteins were recovered, reacted with [14C]‐HCHO in the absence of UDP‐Glc, and polypeptide labeling patterns analyzed by SDS‐polyacrylamide gel electrophoresis and fluorography. This procedure reduced incorporation of label by 5‐ to 8‐fold compared to a procedure omitting the preblocking step, and with enzyme partially purified by solubilization in CHAPS followed by product entrapment, labeling was limited to a small set of polypeptides. Taken together with the results of other studies, the data suggest that one or more polypeptides migrating in the 54–57 kDa region are good candidates for the UDP‐Glc‐binding components of callose synthase.
Internode length in Lathyrus odoratus. The involvement of gibberellins
Authors: Ross John J. , Reid James B. , Davies Noel W. , Murfet Ian C.
Published: May 2006

Evidence was obtained by gas chromatography‐mass spectrometry and gas chromatography‐selected ion monitoring for the presence of gibberellin A20), GA1, GA29, GA8 and 2‐epiGA29 in vegetative shoots of tall sweet pea, Lathyrus odoratus L. Both tall (genotype L–) and dwarf (genotype II) sweet peas elongated markedly in response to exogenous GA1 attaining similar internode lengths at the highest dose levels. Likewise internode length in both genotypes was reduced by application of the GA biosynthesis inhibitor, PP333. The ratio of leaflet length to width was reduced by application of PP333 to tall plants and this effect was reversed by GA1. When applied to plants previously treated with PP333, GA20 promoted internode elongation of L– plants as effectively as GA1, but GA29 was not as effective as GA1 when applied to II plants. In contrast, GA20 and GA1 were equally effective when applied to the semidwarf lb mutant but GA‐treated lblb plants did not attain the same internode length as comparable GA‐treated Lb– plants. The difference in stature between the tall and dwarf types persisted in dark‐grown plants. It is concluded that GA1 may be important for internode elongation and leaf growth in sweet pea. Mutant l may influence GA1 synthesis by reducing 3β‐hydroxylation of GA20 whereas mutant lb appears to affect GA sensitivity.
Internode length in Lathyrus odoratus. Effects of mutants l and lb on gibberellin metabolism and levels
Authors: Ross John J. , Davies Noel W. , Reid James B. , Murfet Ian C.
Published: May 2006

After the application of [13C3H]‐gibberellin A20 to wild‐type (tall) sweet peas (Lathyrus odoratus L.) labelled gibberellin A1 (GA1), GA8, GA29 and 2‐epiGA29 were identified as major metabolities by gas chromatography‐mass spectrometry after high performance liquid chromatography. By contrast in genetically comparable dwarf (II) plants only labelled GA29 and 2‐epiGA29 were produced in significant amounts, although evidence was obtained for trace amounts of labelled GA1 and GA8. The apical portions of dwarf plants contained 8–10 times less GA1 than those of tall plants but at least as much GA20 (measured using di‐deuterated internal standards). In conjunction with previous data these results strongly indicate that in genotype ll internode length is reduced and leaf growth altered by a reduction in GA1 levels attributable to a partial block in the 3β‐hydroxylation of GA20 to GA1.

In contrast to dwarf plants, semidwarf plants (genotype lblb) contained more GA1 in the apical portion than wild‐type counterparts. This is consistent with the suggestion that lb alters some aspect of GA sensitivity.
Effect of copper deficiency on photosynthetic electron transport in wheat plants
Authors: Casimiro Adalcina , Barroso José , Pais Maria Salomé
Published: May 2006

Copper deficiency in wheat (Triticum aestivum L. cv. Nazareno Stramppeli) markedly affects photosynthetic activity. Flag leaves of copper‐deficient plants showed a 50% reduction of the photosynthetic rate expressed as mg CO2 dm−2h−1. The activities of PSI and PSII, determined for isolated chloroplasts, as well as fluorescence measurements on intact leaves of copper‐deficient plants, indicated a low activity of photosynthetic electron transport. Ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity was not affected by copper deficiency but copper deficiency affected the chloroplast ultrastructure, especially at the level of grana, where a disorganization of thylakoids is evident.
Organic acids and cellular changes in the endosperm of Euphorbia lambii seedlings
Authors: Groeneveld H. W. , Idzinga T. M. , Elings J. C.
Published: May 2006

Seedling of Euphorbia lambii Svent. were grown in the dark, and the levels of organic acids in the endosperm were monitored during the 6–7 day period in which all the reserves were depleted. Glycolate, glyoxylate, succinate, fumarate and 2‐oxoglutarate occurred in traces only, the citrate concentration remained rather constant (0.4 μmol endosperm−1), malate varied from 0.2 to 0.4 μmol endosperm−1, but malonate appeared to be the major organic acid in the endosperm ranging from 0.75 to 1.25 μmol endosperm−1. Radioactive malonate was easily taken up by the cotyledons of growing seedlings, and up to 11.2% of the label proceeded to the sterols, the triterpenes and triterpene esters in a 48 h incorporation period. No label from [14C]‐malonate was built into the triacylglycerols in the seedling. Maximum uptake values of 0.6 μmol malonate seedling−1 day−1 were measured, and this value was not altered by a simultaneous uptake of sucrose. Conversely, the uptake of labeled sucrose and its subsequent conversion into sterols and (latex) triterpenes was not altered by a simultaneous uptake of low concentrations of malonate. Increased amounts (from 0.25 μmol malonate seedling−1 and up) caused a 75–90% reduction of both uptake and conversion of sucrose into neutral lipids. To maintain a daily uptake of 4 μmol of sucrose by the cotyledons (required to maintain seedling growth) the simultaneous in vivo uptake of malonate from the endosperm was supposed not to exceed 0.2 μmol seedling−1 day−1.

Thin sections of the endosperm revealed the morphology of the process of reserve depletion. The occurrence of vacuoles 2 days after germination, coincided with the increase in the malonate level. The protein bodies first disappeared completely from the outer layers, whereas the triacylglycerols gradually disappeared from the entire endosperm. About 80% of the endosperm cells contained a large vacuole until the stage of complete depletion, probably serving as the major site of malonate storage.
Identification of polypeptides specific to rachis abscission zone cells of Sambucus nigra
Authors: McManus Michael T. , Osborne Daphne J.
Published: May 2006

Specific polypeptides and antigenic determinants in abscission zone cells of the leaf rachis of Sambucus nigra L. (elderberry) were identified. Extracts from abscission zone tissue (OZ) and from ethylene‐treated abscission zone tissue after separation (Zone) were probed, using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and immunological techniques, for unique peptide components absent from neighbouring non‐zone mid‐rachis tissue (MR). Ouchterlony immuno‐diffusion revealed differences in the spectrum of antigenic determinants possessed by each tissue type when challenged with antiserum raised against OZ. Immuno‐electrophoresis showed a basic polypeptide which is expressed preferentially in the abscission zone.

Immune‐competition of OZ, MR and Zone extracts using immuno‐affinity column chromatography has identified polypeptides of ca 34, ca 32, and ca 28 kDa which are (up to the limits of detection) abscission‐cell specific. An antibody raised against the ca 34 kDa polypeptide recognises a peptide of ca 34 kDa present in OZ and Zone. This peptide is absent from MR.

These results suggest that the specific positional differentiation of ethylene‐responsive target cells which constitute the leaf rachis abscission zone in S. nigra is accompanied by the expression of zone‐cell‐specific antigenic determinants which are not expressed by non‐target neighbouring tissue.
3‐Hydroxypropyl amide formation from 1‐aminocyclopropane‐1‐carboxylic acid by a cell‐free ethylene‐forming system from olive leaves
Authors: Vioque Blanca , Fernández‐Maculet Juan Carlos
Published: May 2006

The low ethylene yield in a cell‐free ethylene‐forming system from olive tree leaves (Olea europaea L. cv. Picual) was investigated. During the incubation, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) was extensively transformed into 3‐hydroxypropyl amide (HPA). Enzyme extract, Mn2+ and oxygen are responsible for this reaction. Horseradish peroxidase (EC 1.11.1.7) can substitute for the enzyme extract in this reaction. HPA formation could be one reason for the poor in vitro conversion efficiency of ACC to ethylene.
Effects of sulfite on phosphoenolpyruvate carboxylase and nicotinamide adenine dinucleotide phosphate‐dependent malate dehydrogenase in epidermal peels in two cultivars of pea
Authors: Zipfel Warren R. , Alscher Ruth Grene , Zucker Laura
Published: May 2006

We have identified a differential response of stomatal conductance to sulfur dioxide in two cultivars of pea (Pisum sativum L. cvs P715 and Nugget). The response to sulfite exposure of PEPC activities present in epidermal peels obtained from the two cultivars was qualitatively in agreement with the results obtained for stomatal conductance. With epidermal tissue isolated from the more sensitive cultivar, we have investigated the effect of light and sulfite on guard cell phosphoenolpyruvate carboxylase (E.E. 4.1.1.31.) and NADP‐dependent malate dehydrogenase (E.C. 1.1.1.82), two enzymes of the malate biosynthetic pathway. No difference was found between the substrate‐saturated activity of phosphoenolpyruvate carboxylase in epidermal tissue incubated in the light or in the dark under the same conditions. Substratesaturated NADP‐dependent malate dehydrogenase activity increased nearly 3‐fold during a 60 min incubation in the light. Incubations of epidermal tissue in the light in the presence of sulfite resulted in a decrease in the activity of both enzymes. Our results suggest that the inhibition of these two enzymes of the malate biosynthetic pathway may be one cause of sulfur dioxide‐mediated stomatal closure.
Internode length and anatomical changes in Pisum genotypes crys and cryc in response to extended daylength and applied gibberellin A1
Authors: Murfet Ian C.
Published: May 2006

Dwarf pea (Pisum sativum L.) plants with genotypes cryc and crys responded differently when an 8 h photoperiod (8 h daylight, 16 h dark) was extended to 24 h (8 h daylight, 16 h incandescent light). Genotype cryc showed up to a 4‐fold increase in internode length, sustained by increases in both cell length (particularly of epidermal cells) and cell number (particularly of cortical cells) while crys plants showed up to a 2‐fold increase in internode length sustained mostly by an increase in cell number. Under an 8 h (daylight) photoperiod the two genotypes did not differ in their sensitivity to applied gibberellin A1 (GA1) and they showed a similar pattern of response. GA1 significantly increased internode length, cell length and cell number in both genotypes. Incandescent light did not increase the size of the response to GA1 except for crys plants at high dose rates of GA1 (29–58 nmol). At saturating doses of GA1 the two genotypes attained a similar peak internode length; incandescent light increased the peak by about 40%. GA1 increased the rate of leaf appearance by up to 33% while incandescent light reduced the rate by 4–7%. The elongation response of the more mature internodes of cryc plants to GA1 or incandescent light was due primarily to an increase in cell length whereas increased cell number made a significant contribution in the case of internodes which were relatively immature at the time the stimulus was applied. The progressive increase in internode length of both genotypes during ontogeny was due primarily to an increase in cell number. In conclusion, alleles cryc and crys (background le La) do not confer a difference in sensitivity to GA1 and the increase in internode length in response to incandescent light is probably not the result of a real or perceived increase in GA1 level. Allele crys may partially block a phytochrome mediated response to light and the key difference between genotypes crys and cryc may lie in the greater elongation (extensibility?) of cryc epidermal cells in incandescent light.
Effect of nitrogen nutrition on amino acid composition of xylem sap and stem wood in Alnus glutinosa
Authors: Tonin G. S. , Wheeler C. T. , Crozier A.
Published: May 2006

Citrulline was the major amino acid in root pressure sap, stem sap and stem wood from Alnus glutinosa L. Gaertn. plants relying on fixed nitrogen or, partly or wholly, on mineral nitrogen for growth. Glutamine increased in prominence in plants assimilating mineral nitrogen but asparagine remained a relatively insignificant component. Differences in the relative amounts of the free amino compounds of stem sap from nitrogen‐fixing and mineral nitrogen‐fed plants were usually small compared to differences between plants fed different sources of mineral nitrogen. In contrast, relatively high values for the ratios of citrulline/total free amino nitrogen compounds and particularly of citrulline/amides in root pressure sap distinguished nitrogen‐fixing plants from those receiving mineral nitrogen. Although the amino acid ratios of stem wood extracts showed closer similarity to those for root pressure sap than stem sap, the seasonal accumulation of citrulline, possibly as a storage amino acid, in stem wood from field‐grown plants negated the possibility of utilising stem wood analyses as an indicator of the form of nitrogen assimilation. Comparative data on the levels of citrulline or other free amino acids in Alnus glutinosa are unlikely to be useful as an index of nitrogen fixation, under most experimental conditions.
The nature of lignin‐like compounds in cucumber hypocotyls induced by α‐1,4‐linked oligogalacturonides
Authors: Robertsen Børre , Svalheim Øystein
Published: May 2006

The nature of the phloroglucinol‐positive material, which is induced in cucumber (Cucumis sativus L.) hypocotyls by α‐1,4‐linked oligogalacturonides, has been investigated by three different experimental approaches and they all suggest that the material may be classified as lignin. Firstly, formation of the material is inhibited by compounds which are known to inhibit the first (phenylalanine ammonia lyase) and the last (peroxidase) step in the biosynthesis of lignin. Secondly, the elicitor enhances incorporation of [14C]‐cinnamic acid derivatives into the hypocotyl cell walls. Thirdly, the analyses of phenols released from cell walls by cupric oxide oxidation show that the walls of oligogalacturonide‐treated hypocotyls contain more polyphenolic material than the walls from intact or wounded hypocotyls. The walls from the oligogalac‐turonide‐treated hypocotyls produce more p‐hydroxybenzaldehyde, p‐hydroxyace‐tophenone, p‐hydroxybenzoic acid and p‐coumaric acid upon oxidation than the other two wall samples. These results suggest that the lignin formed in cucumber hypocotyls in response to oligogalacturonides is mainly derived from p‐coumaryl alcohol.
The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems
Authors: Griffith Marilyn , McIntyre Heather C.H.
Published: May 2006

Root growth, development and frost resistance were examined in winter rye (Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16‐ or 24‐h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24‐h photoperiod in 20°C plants and at a 16‐h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.
Vacuolar ethylene formation does not depend on membrane potential
Authors: Guy Micha
Published: May 2006

Enzymatic synthesis of ethylene in the vacuole is assumed to require membrane integrity. The possibility that this reflects dependence on the vacuolar membrane potential was investigated. Vacuoles were released from protoplasts isolated from leaves of Vicia faba L. cv. Cyprus. The dependence of the ethylene‐forming activity on tonoplast integrity was re‐examined by immobilization of the vacuoles in a cross‐linked polymeric matrix and subsequent permeabilization of the tonoplast with toluene, a pore‐forming reagent. The relationship between the vacuolar ethylene formation and the membrane potential of free vacuoles was investigated by following the uptake of thiocyanate using permeabilized, depolarized and hyperpolarized vacuoles. Toluene and the proton conductor carbonyl cyanide m‐chlorophenylhydrazone (CCCP) caused loss of ethylene‐forming activity and depolarized the vacuolar membrane potential. However, depolarization of the membrane potential with choline chloride and hyperpolarization by ATP did not affect ethylene biosynthesis. These conflicting results lead to the conclusion that vacuolar ethylene biosynthesis is not dependent on the vacuolar membrane potential. The possibility that the inhibition of ethylene biosynthesis by toluene and CCCP may result from direct hydrophobic interactions between these compounds and hydrophobic components of the ethylene‐forming enzyme is discussed.
Nitrate metabolism in roots and nodules ofVicia fabain response to exogenous nitrate
Authors: Caba J. M. , Lluch C. , Hervás A. , Ligero F.
Published: May 2006

Activities of nitrate reduction enzymes, nitrate reductase activity (NRA) and nitrite reductase activity (NiRA) from roots and nodules of 5 mutant genotypes and one commercial cultivar (Alameda) of faba bean (Vicia fabaL. var. minor) grown in the presence of N2alone or with additional NO−3in the medium have been studied. A naturally occurring mutant (VFM109) with impaired ability to reduce nitrate in its nodules is described. All the other cultivars ofV. fabashowed nodule NRA, although the range was very wide, from almost negligible (VFM72) up to 2 μmol h−1(g FW)−1. This activity was entirely of plant origin. Root NRA also ranged widely accross cultivars. However, the level of activity expressed as well as the response of NRA to nitrate followed a pattern opposite to that observed in nodules. Roots and nodules of all cultivars showed very high rates of NiRA, respectively 50 and 150‐fold higher than NRA, thus precluding accumulation of nitrite in these tissues. Root enzymes were significantly stimulated by nitrate while negative (NRA) or little effect (NiRA) was found for nodules. Nitrate and nitrite reduction are carried out by inducible enzymes in roots ofV. fabaand by constitutive enzymes in nodules, indicating that there may be different forms of these enzymes in each tissue. Differences in the plant genotype were a major cause of the variability in nitrate and nitrite reduction by nodulated root systems ofV. faba.
Growth and carbon partitioning in compatible and incompatible peach/plum grafts
Authors: Moing A. , Carbonne F. , Gaudillère J. P.
Published: May 2006

The shoot growth of compatible (Prunus persica L. Batsch cv. Springtime grafted on Prunus cerasifera L. Ehrh cv. Myrobolan P2032) and incompatible (Prunus persica L. Batsch cv. Springtime grafted on Prunus cerasifera L. Ehrh cv. Myrobolan P18) peach/plum grafts was observed over a period of 100 days after grafting under controlled conditions. Leaf and root activities were determined by studying carbon assimilation and partitioning, leaf mineral contents and water relations. Shoot length and leaf number were not significantly affected in the incompatible combination during the first 55 days after grafting, but then, shoot growth rate was significantly reduced. Final total dry weights of the shoot were similar in both graft combinations. The incompatible combination did not show any water stress. Soluble sugar and starch contents increased in the leaves of the incompatible combination, accounting for about 36% of the increase of leaf dry weight per unit area. Photosynthesis was affected by the compatibility of the grafts. Leaf nitrogen content (% dry weight) fell in the incompatible graft combination 65 days after grafting. However, nitrogen content on an area basis was not affected. The possibility of nitrogen stress is discussed.
Studies on cadmium localization in the water fern Azolla
Authors: Sela M. , Fritz E. , Huttermann A. , Tel‐Or E.
Published: May 2006

Uptake of cadmium by the water fern Azolla filiculoides (Lamarck) was characterized, and the localization of the metal in the roots and shoots as well as its effects on some essential elements were studied. Cadmium was accumulated at a rapid rate in Azolla plants within 1 h and then more gradually up to 77 h. Cadmium content was increased in the inner epidermis, cortex and bundle cell walls of the root between 33 and 77 h. This accumulation was characterized by the appearance of small dark grains with high content of cadmium, phosphate and calcium along the epidermal cells. The shoots of Azolla plants grown in the presence of cadmium showed high content of cadmium only in the ventral lobe submerged in the growth medium, suggesting that cadmium was absorbed directly from the medium. The effect of cadmium on essential elements in Azolla was characterized by simultaneous increases in calcium and cadmium content in the root and shoot and by decreases in magnesium content in the root and potassium content in the shoot.
Characterization of two antifungal endochitinases from barley grain
Authors: Jacobsen S. , Mikkelsen J. D. , Hejgaard J.
Published: May 2006

A basic chitinase (chitinase T, EC 3.2.1.14, molecular mass 33 kDa, pI 9.8) was isolated and compared with a previously described chitinase (chitinase C, molecular mass 28 kDa, pI 9.7). The two chitinases were isolated in homogeneous form from barley (Hordeum vulgare L.) Bomi mutant 1508 grains either by two cation exchange steps or by one affinity step followed by cation exchange. Both chitinases are endochitinases with specific activities of 168 and 54 nkat (mg protein)−1 for chitinase T and chitinase C, respectively. Both inhibit the growth of Trichoderma viride efficiently. The lysozyme activity of both chitinases is 104 times lower than that of hen egg‐white lysozyme as measured by lysis of cell walls of Micrococcus lysodeikticus. The amino acid composition and two partial amino acid sequences of chitinase T were determined. A 23 residue sequence of the N‐terminal domain of chitinase T, which was not present in chitinase C, showed 73% identity with domain B of wheat germ lectin and 65% identity with the N‐terminal domain of an endochitinase from bean leaves (deduced from cDNA). A 9 amino acid sequence of a cyanogen bromide fragment of chitinase T was identical with a cDNA deduced sequence of a barley aleurone endochitinase but differed in one residue from chitinase C. Generally, the two grain chitinases have physico‐chemical and enzymatic properties similar to the plant leaf chitinases characterized. Both chitinases are localized in the aleurone layer and starchy endosperm of developing and germinating grain, but not in the embryo. The appearance of chitinases T and C at a late state of grain development suggests a role for these enzymes as a defense against fungi in the quiescent and germinating grain.
Growth capacity and molecular mass distribution of cell wall polysaccharides along the hypocotyl of Pinus pinaster
Authors: Lorences Ester P. , Revilla Gloria , Acebes José Luis , Zarra Ignacio
Published: May 2006

The changes in the endogenous growth as well as in the cell wall composition were studied along the hypocotyl of Pinus pinaster Aiton. Cell elongation decreased as the distance from the cotyledonary node increased. Pectic polysaccharides underwent an important depolymerization accompanied by a decrease in their uronic acid content from the apical to basal region of the hypocotyl. Additionally, the molecular mass of pectic polysaccharides strongly decreased from the apical to the basal regions. Watersoluble hemicellulosic polysaccharides extracted with 4% KOH decreased notably from the cotyledonary node towards the base, while water‐soluble polysaccharides extracted with 24% KOH showed few differences along the hypocotyl. The molecular mass of xyloglucan present in both hemicellulosic fractions was lower in the upper hypocotyl region as compared with the basal region. These findings are in agreement with an active xyloglucan depolymerization in the upper region as would be expected in a region exhibiting very active growth.
Purification of plant peroxisomes in iso‐osmotic metrizamide
Authors: Turley Rickie B. , Trelease Richard N.
Published: May 2006

Methods were developed for isolating highly‐purified peroxisomes under iso‐osmotic conditions from 3 plant parts, namely cotyledons of cotton (Gossypium hirsutum L.) seedlings, endosperm of castor bean (Ricinus communis L.) seedlings and leaves of mature spinach (Spinaca oleracea L.) plants. Purification was achieved by sedimentation of the organelles into metrizamide gradients centrifuged in a vertical rotor (VTi 50). Gradients consisted of an upper transition layer (1:1 mixture of homogenizing medium and 0.25 M metrizamide), a linear 0.25–0.76 M metrizamide gradient and a 0.76 M metrizamide pad. Peroxisomes from all 3 plant parts were recovered in a major band at a density ranging from 1.24 to 1.27 g cm−3, which is a density range similar to that for peroxisomes isolated in sucrose gradients. The percent of the total gradient cytochrome c oxidase (mitochondria marker) activity recovered in peroxisome fractions ranged from 1.5% in endosperm to 2.8% in leaves, while a plastid marker (chlorophyll or galactosyl transferase activity) ranged from undetectable in leaf peroxisome fractions to 3.6% in endosperm peroxisome fractions. Intactness of the peroxisomes was judged to be 69%, 89% and 78% for the cotyledon, endosperm and leaf peroxisomes, respectively. Isolated peroxisomes were stable for at least 5 h in metrizamide medium. Microscopic (bright‐field and transmission electron microscopy) assessments verified that the peroxisomes were morphologically intact and fractions were essentially free of contaminating organelles. Metrizamide is an excellent iso‐osmotic medium for purifying peroxisomes from these plant organs and tissue.
Habituation: cultural curiosity or developmental determinant?
Authors: Jackson J. A. , Lyndon R. F.
Published: May 2006

The induction and reversal of habituation for auxin or cytokinin have been brought about by exposure of callus tissue to low or high concentrations of the growth substance in question. Since the growth rate of the tissues must be measured in the presence or absence of the growth substance being tested, habituation can be demonstrated only in callus. However some developmental processes in the intact plant seem to imply the possible involvement of habituation‐like processes in normal development. Evidence for this, and the implications for the action of growth substances in plant development are considered.
On the periodic minimal surface structure of the plant prolamellar body
Authors: Lindstedt I. , Liljenberg C.
Published: May 2006

An evaluation of minimal surface structures formed in lipid‐water systems and in lipid‐protein‐water systems in relation to electron microscopic data on the prolamellar body are reported. It is suggested that the characteristic square and hexagonal patterns seen in electron micrographs of prolamellar bodies constitute minimal surfaces of the P‐ and D‐type, respectively. The existence of the G‐ and the H‐surface in the membrane systems of prolamellar bodies is discussed.
Effects of UV‐B radiation on soybean yield and seed quality: a 6‐year field study
Authors: Teramura Alan H. , Sullivan Joe H. , Lydon John
Published: May 2006

Two soybean [Glycine max (L.) Merr.] cultivars, Essex and Williams, were grown in the field for 6 consecutive seasons under ambient and supplemental levels of ultravio‐Set‐B radiation to determine the potential for alterations in yield or seed quality with a reduction in the stratospheric ozone column. The supplemental UV‐B fluences simulated a 16 or 25% ozone depletion. The data presented here represent the first field experiment conducted over multiple seasons which assesses the effects of increased UV‐B radiation on seed yield. Overall, the cultivar Essex was found to be sensitive to UV‐B radiation (yield reductions of 20%) while the cultivar Williams was tolerant. However, the effectiveness of UV‐B radiation in altering yield was strongly influenced by the seasonal microclimate, and the 2 cultivars responded differently to these changing factors. Yield was reduced most in Essex during seasons in which water availability was high and was reduced in Williams only when water was severely limiting. The results of these experiments demonstrate the necessity for multiple‐year experiments and the need to increase our understanding of the interaction between UV‐B radiation and other environmental stresses in order to assess the potential consequences of stratospheric ozone depletion.
Correlation between nitrogenase and glutamine synthetase expression in the cyanobacterium Anabaena cylindrical
Authors: Renström‐Keliner Eva , Rai Amar N. , Bergman Birgitta
Published: May 2006

Distribution pattern and levels of nitrogenase (EC 1.7.99.2) and glutamine synthetase (GS, EC 6.3.1.2) were studied in N2‐, NO3− and NH4+ grown Anabaena cylindrica (CCAP 1403/2a) using immunogold electron microscopy. In N2‐ and NO3− grown cultures, heterocysts were formed and nitrogenase activity was present. The nitrogenase antigen appeared within the heterocysts only and showed an even distribution. The level of nitrogenase protein in the heterocysts was identical with both nitrogen sources. In NO3− grown cells the 30% reduction in the nitrogenase activity was due to a corresponding decrease in the heterocyst frequency and not to a repressed nitrogenase synthesis. In NH4− grown cells, the nitrogenase activity was almost zero and new heterocysts were formed to a very low extent. The heterocysts found showed practically no nitrogenase protein throughout the cytoplasm, although some label occurred at the periphery of the heterocyst. This demonstrates that heterocyst differentiation and nitrogenase expression are not necessarily correlated and that while NH4+ caused repression of both heterocyst and nitrogenase synthesis, NO3− caused inhibition of heterocyst differentiation only. The glutamine synthetase protein label was found throughout the vegetative cells and the heterocysts of all three cultures. The relative level of the GS antigen varied in the heterocysts depending on the nitrogen source, whereas the GS level was similar in all vegetative cells. In N2‐ and NO3+ grown cells, where nitrogenase was expressed, the GS level was ca 100% higher in the heterocysts compared to vegetative cells. In NH4+ grown cells, where nitrogenase was repressed, the GS level was similar in the two cell types. The enhanced level of GS expressed in heterocysts of N2 and NO3− grown cultures apparently is related to nitrogenase expression and has a role in assimilation of N2derived ammonia.
Changes in the levels of enzymes involved in ammonia assimilation during the development of Phaseolus vulgaris seedlings.Effects of exogenous ammonia
Authors: León Elena , de la Haba Purificación , Maldonado José M.
Published: May 2006

Seeds of Phaseolus vulgaris L. cv. White Kidney were germinated and grown either in a nitrogen‐free or in an ammonia‐supplied medium. The changes in the soluble protein concentration and in the levels of glutamine synthetase (GS, EC 6.3.1.2), NADH–glutamate synthase (NADH‐GOGAT, EC 1.4.1.14), ferredoxin‐glutamate synthase (Fd‐GOGAT, EC 1.4.7.1) and glutamate dehydrogenase (GDH, EC 1.4.1.2), both NADH‐ and NAD+‐dependent, were examined in cotyledons and roots during the first 10 days after sowing. Soluble protein declined rapidly in the cotyledons and increased slightly in the roots. GS activity was initially high both in cotyledons and roots but subsequently decreased during seedling growth. Exogenous ammonia hardly affected GS activity. High levels of NADH‐GOGAT were present both in cotyledons and roots during the first days of germination. The activity then gradually declined in both organs. In contrast, Fd‐GOGAT in cotyledons was initially low and progressively increased with seedling development. In roots, the levels of Fd‐GOGAT were higher in young than in old seedlings. Supply of ammonia to the seedlings increased the levels of NADH‐GOGAT and Fd‐GOGAT both in cotyledons and roots. NADH‐GDH (aminating) activity gradually increased during germination. In contrast, the levels of NAD+‐GDH (deaminating) activity were highest during the first days of germination. Exogenous ammonia did not significantly affect the activities of GDH.
Improvement of nutrient medium for growth and embryogenesis of megagametophyte and embryo callus lines of Picea abies
Authors: Simola Liisa Kaarina , Santanen Arja
Published: May 2006

New macro and microelement solutions were formulated for stimulation of growth and embryogenesis in white and chlorophyllous megagametophyte and embryo callus lines of Picea abies (L.) Karst. Macroelement media with different NH4+ and NO3− ratios (1:2 and 1:4), the increased level of several microelements and the effect of organic nitrogen (100 mg 1−1 casein hydrolysate, 0.25 mM arginine and 0.5 mM glutamine) were tested with 4 combinations of growth regulators (2,4‐dichlorophe‐noxyacefic acid or indole‐3‐butyric acid, kinetin). Green chlorophyll‐containing, in contrast to white callus lines, grew quite well without exogeneously added organic nitrogen. The ratio between NH4+ and NO3− was not significant. The increased levels (μM) of several microelements: B (200), Zn (50), I (25), Cu (1), Co (0.5) and in addition Ni (0.1) improved callus growth in some lines more than 50% (DW) compared to cultures grown on the micronutrients of Murashige and Skoog. The response of different callus lines varied with the combinations of growth regulators. Embryogenesis did not occur in chlorophyllous callus lines in any of the 24 media combinations tested, but some very good media could be found for white megagametophyte and embryo callus lines. Microelements, favourable combination of growth regulators and organic nitrogen were especially important. A megagametophyte callus subcultured for 4 years was also able to form numerous proembryos.
Characterization of a shiitake mutant strain producing ballshaped fruiting bodies
Authors: Itävaara Merja
Published: May 2006

Growth characteristics of a spontaneous mutant of shiitake Lentinula edodes (Berk.) Pegler were studied. The mutant was first detected as a result of changes in the growth habit of the normal strain in the liquid medium. Abundant formation of aerial hyphae was distinctive. In sawdust logs the mutant strain produced abnormal basidiocarps, lacking stipe, gill and spore formation.

Growth rates of the normal and the mutant strain were compared in two liquid media: malt‐yeast extract and Leatham's medium. The increase in dry weight of the mutant's mycelium was much higher than that of the wild type in both media, which indicated better adaptation to liquid culture. In the sawdust, however, growth of the mutant was slower than that of the normal strain. The mutant's intracellular protein content was lower than that of the normal strain. The pH of the liquid cultures differed: the wild type decreased the pH during growth, while the mutant increased the pH. Comparison of the protein and esterase isoenzyme profiles of the vegetative hyphae of both strains indicated profound differences. One protein (pI 6.5, 39 kDa), which in earlier studies has been found to be typical of L. edodes species, was absent from the mutant's profile. Differences in the esterase profile were also clear.