bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variation in hydrochloric acid, malic acid, and calciumions secreted by the trichomes of chickpea (Cicer arietinum)
Authors: Lazzaro Mark D. , Thomson William W.
Published: May 2006

The concentrations of malate. calcium ions. hydrogen ions, and chloride ions were measured in secretions collected between June 1991 and May 1992 from the secretory trichomes of chickpea (Cicer arietinum L.). The average malate concentration was 114 mM and varied from 2 to 287 mM, the average chloride ion concentration was 177 mM and varied from 68 to 355 mM. and the average calcium ion concentration was 0.82 mM and varied from 0.24 to 1.97 mM. The variability in malate. chloride ions, and calcium ions closely followed the sinusoidal variation in the amount of solar radiation per day throughout the year (Riverside. CA. USA). Also. 77% of the variation in malate concentration, 51% of the variation in chloride ion concentration, and 67% of the variation in calcium ion concentration in collected secretions was directly dependent on the day of the year. In addition, the average hydrogen ion concentration was 299 mM, which corresponds to a pH of 0.52. Although the concentration of hydrogen ions varied from 195 mM (pH 0.71) to 417 mM (pH 0.38) throughout the year, the variation did not follow any clear pattern with respect to the day of the year. These data suggest that malate. chloride ion, and calcium ion secretion are linked to the amount of daily sunlight and to the day of the year while the pH of secretions is not directly linked to light level.
Increase in permeability to oxygen and in oxygen uptake of soybean nodules under limiting phosphorus nutrition
Authors: Ribet Jérome , Drevon Jean‐Jacques
Published: May 2006

The O2 uptake of soybean roots nodulated with Bradyrhizobium japonicum strain PJ 17 and its response to external oxygen pressures (pO2) were measured in situ, 40–45 days after sowing (DAS). on plants grown hydroponically with either limiting (low‐P) or non‐limiting (control) orthophosphate (P1) supplied weekly. At this age. school mass, nodule mass and number of nodules of low‐P plants were respectively 35. 14 and 26% of those of control plants, whereas root mass was not significantly affected by P nutrition. The mean individual mass and size of nodules were also lower in low‐P plants. The rate of O2 or growth and maintenance of root and nodule tissue of low‐P plants was 35% of control values. By contrast. the nodule nitrogenase‐linked O2 uptake and the nodule permeability to O2 of low‐P plants were respectively 210 and 190% of those of control plants at ambient pO2 However. P deficiency did not significantly affect the specific acetylene reducing activity of nodule nitrogenase at 45 DAS nor the ratio of whole plant N fixed to nodule mass at 75 DAS. It is argued that P deficiency induces an increase in nodule O2 uptake per electron transfered by nitrogenase and an alteration in the structural features of nodules that are related to permeability to O2.
Light‐modulation of nitrate reductase activity in leaves and roots of maize
Authors: Merlo Lucia , Ferretti Massimo , Passera Calvino , Ghisi Rossella
Published: May 2006

In order to examine the light‐modulation of nitrate reductase (NR: EC 1. 6.6.1) activity in tissues of maize (Zea mays L. cv. Plauto). the enzyme was assayed under both selective (5 mM, Mg2+) and unselective conditions (2 mM EDTA; Vmax). in leaf and root extracts from seedlings transferred from high irradiance (HI: 450 μmol m−2s−1 PAR) to shade (200 μmol m−2 s−1) or to darkness. The corresponding changes in tissue nitrate were also evaluated. The results show that maize leaf NR activity (NRA) is subjected to reversible light‐modulation involving rapid changes in the sensitivity of the enzyme to inhibition by Mg2+, In fact, NR assayed in the presence of Mg2+ lost about 60% and 20% of its activity after 30 min in the dark and in the shade, respectively. Vmax started to decrease only after 1–3 h. depending on the extent of light reduction. Deactivation in the shade was reversed in vivo by returning the plants to HI. the kinetics of reactivation being similar to those of deactivation. Following dark‐deactivation in vivo, spontaneous reactivation of leaf NR occurred during in vitro incubation at 25°C. and the process was accelerated by AMP. The NR from HI‐leaves was deactivated (half‐time 2 min) by incubation with MgATP. but the extent of the in vitro deactivation was small. Maize root NR was more sensitive to Mg2+ than leaf NR, with 5 mM Mg2+ causing a 50% inhibition of the activity in HI‐roots. In contrast to leaves, marked changes in the Mg2+‐sensitivity of maize root NRA became apparent only after 3 h in the dark or in the shade, when Vmax had also declined significantly.
A 2,4‐D‐inducible glutathione S‐transferase from soybean (Glycine max). Purification, characterisation and induction
Authors: Flury Thomas , Adam Daniel , Kreuz Klaus
Published: May 2006

Glutathione S‐transferases (GSTs; EC 2.5.1.18) have recently been proposed to form one large group among the auxin‐induced proteins. However. the properties and regulation of such auxin‐responsive GSTs in the plant still await detailed investigation. In this study, a 2,4‐dichloro‐phenoxyacetic acid (2,4‐D)‐inducible GST isozyme from soybean (Glycine max [L.] Merr. cv. Williams) was purified to near homogeneity by anion‐exchange and affinity chromatography on S‐hexylglutathione agarose. The native enzyme had a molecular mass of 49 kDa, as determined by gel filtration, and consisted of 26‐kDa subunits. The purified GST conjugated glutathione to 1‐chloro‐2,4‐dinitrobenzene and to the herbicide metolachlor, but not to the other GST substrates atrazine. fluorodifen or trans‐cinnamic acid. The N‐termmal amino acid sequence shared significant homology with the deduced polypeptide sequences of two 2,4‐D‐inducible genes from tobacco, par A and CNT107. The levels of the 26‐kDa GST subunit protein in soybean hypocotyls were analysed by immunoblotting. At micromolar concentrations, 2,4‐D induced a transient increase in net accumulation of GST, whereas indole‐3‐acetic acid or I‐naphthaleneacetic acid did not increase the GST levels. Known inhibitors of polar auxin transport, including 2.3.5‐tri‐iodobenzoic acid. N‐I‐naphthylphthalamic acid and analogues thereof, differed widely in their ability to elicit GST protein accumulation. It is concluded that the induction of soybean GST by 2,4‐D and by some of the auxin transport inhibitors is not related to auxin activity or to changes in the endogenous auxin levels.
Synthesis of jasmonate‐induced proteins in barley (Hordeum vulgare) is inhibited by the growth retardant tetcyclacis
Authors: Wasternack Claus , Atzorn Rainer , Leopold Jens , Feussner Ivo , Rademacher Wilbelm , Parthier Benno
Published: May 2006

BarJey leaf segments treated with jasmonate respond with the synthesis of specific proseins, referred to as jasmonate‐induced proteins (JIPs). Application of abscisic acid (ABAl also induced JIP synthesis (Weidhase et al. 1987). In this study the effects of inhibitors on sorbitol‐induced increases of endogenous jasmonates and ABA were investigated. The promotion of jasmonates by sorbitol was inhibited by the growth retardant tetcyclacis at concentrations as low as 1 ftM. In parallel with the decrease of jasmonates, JIP gene expression was reduced as reflected by a decline in the level of a 23‐kDa protein UIP‐23) and mRNAs of JIP‐6 and JIP‐23. 12‐Oxo‐phytodienoic acid, an inlermediale in the lipoxygenase (LOX) pathway leading to jasmonic acid was able to overcome the inhibition by tetcyclacis and increases both the endogenous jasmonate content and transcript accumulation. This suggests that tetcyclacis acts upstream of 12‐oxo‐phytodienoic acid and in keeping with this proposal, an increase in relative LOX activity was detected after tetcyclacis treatment. Although tetcyclacis was shown to inhibit the degradation of ABA to phaseic acid, its effect on jasmonate synthesis is much more pronounced.
Plant regeneration from protoplasts of sugar beet (Beta vulgaris)
Authors: Lenzner Steffen , Zoglauer Kurt , Schieder Otto
Published: May 2006

Mesophyll protoplasts from two of five sugar beet lines tested were regenerated into plants. Mesophyll protoplasts of all lines showed high plating efficiencies up to 4.0% developed hard compact callus, and two of the lines also developed white, soft and friable callus consisting of starch grain‐containing cells. Whereas the compact callus never regenerated into plants, the white friable ones frequently developed globular structures, which became green in the light and formed adventitious shoots after cytokinin (BAP or thidiazuron) treatment. Genetic analysis by PCR‐fingerprinting and flow cytometry showed uniformity and unchanged ploidy levels in 15 independently regenerated plantlets in line NF. but altered ploidy level (from diploid to triploid) in a regenerated plantlet of clone VRB.
NADP+‐isocitrate dehydrogenase in germinating and senescing pumpkin cotyledons
Authors: Nieri Barbara , De Bellis Luigi , Biagi Pier Paolo , Alpi Amedeo
Published: May 2006

NADP+‐isocitrate dehydrogenase (IDH, EC 1.1.1.42) was studied during the post‐germinative growth of pumpkin (Cucurbita pepo L. cv. Alberello di Sarzana) seedlings. In cotyledons. IDH activity increased in the dark and declined after illumination. Native PAGE showed that at least two isozymes of low electrophoretic mobility are present in cotyledons and absent in other pumpkin tissues. Anion exchange chromatography performed on extracts both from 4‐day‐old etiolated cotyledons and from illuminated cotyledons confirmed the trend of the IDH isoforms. In senescing cotyledons an additional IDH isoform with higher electrophoretic mobility appears. Overall the data indicate the presence of specific NADP+‐IDH isoforms in etiolated cotyledons and senescing cotyledons, when glyoxylate cycle enzymes are active. A possible role for these IDH isoforms is proposed.
Molecular aspects of heterosis in plants
Authors: Tsaftaris S. Athanasios
Published: May 2006

Since Shull's original description of heterosis, breeders have made wide use of this phenomenon. However, while agronomists have been utilizing heterosis as a means of improving crop productivity, the biological basis of heterosis remains unkown. It is generally believed that our understanding of heterosis will enhance our ability to form new genotypes which may be used directly as F1 hybrids or form the basis for future selection programmes. While the original concept of heterosis resulted from studies at the phenotypic morpohological level, they were soon followed by biochemical data with the advent of electrophoresis and the consequent ease of accumulation of data related to isozyme variability. However, the large number of restriction fragment length polymorphisms from more recent studies has allowed the development of linkage maps with a high degree of resolution useful in locating and manipulating quantitative trait loci (QTL). When substantial numbers of such neutral markers were used to measure genetic distance in large numbers of maize inbreds, very significant correlations were recorded between parental genetic distance and hybrid performance. Through the same approach, a relatively small number of QTLs dispersed through the maize genome were identified which show clear overdominance expression controlling heterosis.

The hypothesis was made that some QTLs could code for regulatory proteins since these proteins are able to control a vast array of other structural genes, the products of which are necessary for the expression of complicated characters such as yield and heterosis for yield. The few such proteins identified thus far are all multimeric proteins with the heteropolymers exhibiting significantly different activities in comparison with the homopolymers, that is in compliance with the clear overdominance manifestation of the few QTLs analyzed so far.

In addition, parameters derived from the variability of genome expression assessed through studies of polymorphisms in the amounts of individual proteins or mRNAs show numerous significant correlations between these indices and hybrid vigor. These correlations supported the conclusion that QTLs could be loci controlling the amount of mRNAs or proteins synthesized from a number of structural genes, and stress the significance of both the regulatory proteins (and their encoding genes) and the structural genes, being regulated, in manifestation of complicated characters, such as heterosis.
Differential expression of cytosolic and plastid pyruvate kinase isozymes in tobacco
Authors: McHugh Sylvia G. , Knowles Vicki L. , Blakeley Stephen D. , Sangwan Rajender S. , Miki Brian L. , Dennis David T. , Plaxton William C.
Published: May 2006

The expression of cytosolic and plastid pyruvate kinase (PK; E.C. 2.7.1.40) in various tissues of tobacco (Nicotiana tabacum cv. Petit Havana SR1) was investigated. To facilitate this study, a cDNA clone for cytosolic pyruvate kinase (PKc) was isolated from a tobacco seed cDNA expression library. This cDNA has an open reading frame capable of encoding a 508‐amino acid polypeptide with a predicted molecular mass of 55.1 kDa. The deduced amino acid sequence has 76% identity with the sequence of potato PKc. Southern blot analysis shows that N. tabacum contains two copies of the PKc gene, each derived from the single gene found in its progenitors, N. tomentosiformis and N. sylvestris. Northern blots detected a 1.9‐kb band in flower, seed, root, stem and leaf tissues of N. tabacum. Immunoblotting using anti‐[castor oil seed (COS) PKc]‐immunoglobulin G (IgG) detected 58‐ and 56‐kDa polypeptides in all tobacco tissues examined. In developing seeds, mRNA levels were low except for a peak at 8 days post anthesis (dpa), whereas the highest level of the PKc polypeptides was detected 10–16 dpa. The persistence of PKc well after the peak in mRNA levels suggests that PKc is stable in developing seeds. Our previous studies have shown that leucoplast PK (PKp) mRNA could be detected throughout tobacco seed development as well as in somatic tissues. In developing seeds, steady state PKc mRNA levels showed a broad peak of accumulation from 8–20 dpa, reaching maximum levels at 16 dpa. In the present study, polypeptides of 63 and 60 kDa were detected on immunoblots probed with anti‐(COS PKp)IgG in developing tobacco seeds 10–20 dpa. The observed pattern of PKp protein accumulation closely correlated with the profile of steady state mRNA levels suggesting that this isoenzyme has a much greater rate of turnover than that of PKc. In contrast to PKc, there was no detectable accumulation of PKp protein at other times during seed development or in somatic tissues even though significant levels of PKp mRNA could be detected. The differences in the protein accumulation and mRNA expression patterns of PKc and PKp suggest that the tissue‐specific and developmental expression of these isoenzymes in tobacco may be controlled by independent transcriptional and post‐transcriptional mechanisms.
Effects of UV‐B radiation and nitrogen starvation on enzyme activities in isolated plasma membranes of Euglena gracilis
Authors: Petersen‐Mahrt Silja K. , Ekelund Nils G. A. , Widell Susanne
Published: May 2006

Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellate Euglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV‐B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane‐bound enzymes. Also, we wanted to see whether stress‐induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two‐phase partitioning was successful, as judged by the large enrichment of the plasma membrane‐marker 5′‐nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared.

Two other enzymes were analyzed, K+, Mg2+‐ATPase, and adenylyl cyclase. The specific activities of all three enzymes were decreased by UV‐B radiation by ca 30–50%, compared with the control cultures. On the other hand, nitrogen deficiency not only reduced the activity of the K+.Mg2+‐ATPase but also increased the activities of the 5′‐nucleotidase and adenylyl cyclase. The different treatments also resulted in differences in polypeptide pattern, e.g., a polypeptide around 30 kDa seemed to be specific to plasma membranes of nitrogen‐deficient cultures and one at 39 kDa for the UV‐B radiated ones.

All three enzymes showed diurnal rhythms that were affected by UV‐B radiation. The peak in the rhythm of the ATPase was shifted by UV‐B radiation, the rhythm of the 5′‐nucleotidase nearly eliminated. The first peak of adenylyl cyclase activity was delayed, so that it looked more like a broad peak between 2 and 11 h after the onset of light. The rhythm of ATPase activity could be correlated with that of photosynthesis in both control and UV‐B irradiated cultures. Also, the rhythms of adenylyl cyclase activity and cell shape changes showed some similarities.
A critique of the use of inhibitors to estimate partitioning of electrons between mitochondrial respiratory pathways in plants
Authors: Millar A. H. , Atkin O. K. , Lambers H. , Wiskich J. T. , Day D. A.
Published: May 2006

The contribution of individual plant mitochondrial respiratory pathways to total respiration is commonly assessed by titration with specific inhibitors of different components in the branched electron transport chain. A pathway's contribution is equal to the activity when the other branch is blocked by an inhibitor multiplied by the degree (0‐1.0) to which this activity is engaged when both pathways are operating. According to Bahr and Bonner (1973. J. Biol. Chem. 218: 3441–3445) the plot of the activities of identical titrations, one performed in the absence and the other in the presence of a specific inhibitor of the other branch of the respiratory chain, yields a straight line whose slope indicates the engagement of the titrated pathway during uninhibited respiration. An initial slope of zero may occur if electron flux is diverted between pathways during titrations. However, beyond the breakpoint (representing the point of pathway saturation), a straight line is obtained with a slope representing engagement. This technique assumes that the kinetics of inhibiting a specific component of the respiratory chain are independent of the absolute rate of electron flux through the total pathway. To test this assumption, the activity of respiratory pathways in isolated soybean (Glycine max [L]. Merr. cv. Stevens) mitochondria was titrated with specific inhibitors of the cytochrome and alternative oxidases. Under these conditions, the electron flux through a given pathway was manipulated by poising the rate of succinate oxidation with the succinate dehydrogenase inhibitor malonate. Construction of activity plots in the presence versus absence of malonate failed to result in straight lines for either KCN (when titrating the cytochrome pathway) or salicylhydroxamic acid (when titrating the alternative pathway). Rather, the resultant plots were always curvilinear whenever the activity in the presence of malonate divided by the activity in the absence of malonate was less than 1.0. In no case could the real engagement of the pathway be precisely estimated from the titration data. Titrations of cytochrome pathway activity in isolated potato tuber (Solanum tuberosum L. cv. Sabago and Canabex) mitochondria (which lack the alternative oxidase) showed that as the inhibitor concentration was increased, so did the reduction status of the ubiquinone pool, to a new steady state. The dependence of inhibition kinetics on the rate of flux through the pathway, and the increase in ubiquinone pool reduction upon KCN addition, are explained in terms of the elasticity of component enzymes as outlined in the theory of metabolic control analysis. The implications of this finding for the use of titrations to estimate engagement of plant respiratory pathways are discussed.
On the use of antibiotics to reduce rhizoplane microbial populations in root physiology and ecology investigations
Authors: Smart David R. , Ferro Ari , Ritchie Karl , Bugbee Bruce G.
Published: May 2006

No straightforward method exists for separating the proportion of ion exchange and respiration due to rhizoplane microbial organisms from that of root ion exchange and respiration. We examined several antibiotics that might be used for the temporary elimination of rhizoplane bacteria from hydroponically grown wheat roots (Triticum aestivumcv. Veery 10). Each antibiotic was tested for herbicidal activity and plate counts were used to enumerate bacteria and evaluate antibiotic kinetics. Only ‐lactam antibiotics (penicillins and cephalosporins) did not reduce wheat growth rates. Aminoglycosides, the pyrimidine trimethoprim, colistin and rifampicin reduced growth rates substantially. Antibiotics acted slowly, with maximum reductions in rhizoplane bacteria occurring after more that 48 h of exposure. Combinations of nonphytotoxic antibiotics reduced platable rhizoplane bacteria by as much as 98%; however, this was generally a reduction from about 109to 106colony forming units per gram of dry root mass, so that many viable bacteria remained on root surfaces. We present evidence which suggests that insufficient bacterial biomass exists on root surfaces of nonstressed plants grown under well‐aerated conditions to quantitatively interfere with root nitrogen absorption measurements.
Optimal leaf area indices in C3 and C4 mono‐ and dicotyledonous species at low and high nitrogen availability
Authors: Anten N. P. R. , Schieving F. , Medina E. , Werger M. J. A. , Schuffelen P.
Published: May 2006

From an analytical model it was shown that for a given total amount of nitrogen in the canopy, there exists an optimal leaf area index (LAI), and therefore an optimal average leaf introgen content, at which canopy photosynthesis is maximal. If the LAI is increased above this optimum, increased light interception will not compensate for reduction in photosynthetic capacity of the canopy resulting from reduced leaf nitrogen contents. It was further derived from the model that the value of the optimal LAI increases with the photosynthetic nitrogen use efficiency (PNUE) and decreases with the canopy extinction coefficient for light (KL) and incident photon flux density (PFD) at the top of the canopy. These hypotheses were tested on dense stands of species with different photosynthetic modes and different architectures. A garden experiment was carried out with the C4 monocot sorghum (Sorghum bicolor [L.] Moensch cv. Pioneer), the C3 monocot rice (Oryza sativa L. cv. Araure 4), the C4 dicot amaranth (Amaranthus cruentus L. cv. K113) and the C3 dicot soybean (Glycine max [L.] Merr. cv. Williams) at two levels of nitrogen availability.

The C4 species had higher PNUEs than the C3 species while the dicots formed stands with higher extinction coefficients for light and had lower PNUEs than the monocots. The C4 and monocot species were found to have formed more leaf area per unit leaf nitrogen (i.e., had lower leaf nitrogen contents) than the C3 and dicot species, respectively. These results indicate that the PNUE and the extinction coefficient for light are important factors determining the amount of leaf area produced per unit nitrogen as was predicted by the model.
Inhibition of oleic acid incorporation into a non‐lipid fraction by chloroacetamide herbicides
Authors: Kring Friedhelm , Couderchet Michel , Böger Peter
Published: May 2006

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I50= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non‐lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [14C]‐oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non‐herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta‐bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non‐lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these herbicides.
Intracellular localization of sucrose‐phosphate phosphatase in storage cells
Authors: Echeverria Ed
Published: May 2006

The intracellular location of sucrose‐phosphate phosphatase (SPP; EC 3.1, 3.24) was investigated by comparing the ratios of SPP to vacuolar and cytosolic markers in protoplasts and vacuoles from storage tissues of red beet (Beta vulgaris) and turnip (Brassica rapa L. var. rapa) hypocotyl, and carrot (Daucus carota) root. In all three instances, SPP activity was found not to be associated with vacuolar markers ß‐acetyl‐glucosaminidase and α‐mannosidase, but proportionally associated with the cytosolic marker alcohol dehydrogenase. It was determined that in storage cells of red beet and turnip hypocotyl, as well as in carrot root, SPP is located in the cytoplasm. Discrepancies with earlier reports indicating SPP of vacuolar origin are discussed.
Relations between cytokinin level, bud development and apical control in Norway spruce, Picea abies
Authors: Bollmark Marie , Chen Hao‐Jie , Moritz Thomas , Eliasson Lennart
Published: May 2006

In conifers such as Norway spruce, the extent of shoot growth is predetermined by the size and number of embryonal organs of the buds laid down the previous year. As it is known that cytokinins have a key role in bud development a possible hypothesis is that the level of cytokinin in the buds during their formation determines their size and complexity. As a first step to test this hypothesis we compared cytokinin levels in buds of different size of annual shoots from 15‐ to 20‐year‐old trees of Picea abies (L.) Karst. Apical buds from the leaders, and from branches in lower parts of the trees, were collected in April, July and August. The difference in size of the buds and the shoots growing from them was considerable in these three positions. Extracts were purified by immunoaffinity columns, and the retained compounds were separated by high‐performance liquid chromatography (HPLC). Quantification was made by enzyme‐linked immunosorbent assay (ELISA), and the accuracy of this method was checked by measurements with liquid chromatography‐mass spectrometry (LC‐MS) and UV absorption. Zeatin riboside (ZR) was the most abundant cytokinin, but isopentenyladenosine (iPA) was also present in all samples. The large apical bud of the leader contained much higher cytokinin concentrations than the considerably smaller buds from lower positions, and during the period of secondary growth in July, similar relationships were found for annual stem tissue from different positions. The possible role of ZR as a controlling factor in bud development and apical control is discussed. Our conclusion is that the level of zeatin‐type cytokinins appears to play an important role in the establishment of differences in bud size and, thereby, the architecture of the tree crown.
Induction of phenylpropanoid and tyramine metabolism in pectinase‐ or pronase‐elicited cell suspension cultures of tobacco (Nicotiana tabacum)
Authors: Negrel Jonathan , Javelle Francine
Published: May 2006

The induction of the phenylpropanoid pathway and of tyramine metabolism was monitored in cell suspension cultures of Nicotiana tabacum treated with cell wall‐degrading enzymes, in an attempt to correlate the synthesis of hydroxycinnamic acid amides of tyramine with the formation of wall‐bound phenolic polymers. Treatment with commercial pectinase (from Penicilium occitanis) induced a rapid rise in phenylalanine ammonia‐lyase (EC 4.3.1.5), 4‐coumarate:CoA ligase (EC 6.2.1.12), tyramine hydroxycinnamoyltransferase (EC 2.3.1.110) and peroxidase (EC 1.11.1.7) activities, and a concomitant decline in cinnamyl alcohol dehydrogenase (EC 1.1.1.195) activity. The induction of the phenylpropanoid pathway and of the synthesis of cinnamoyl‐tyramines preceded the death of a large proportion of the elicited cells. When the cultures were treated with pronase (from Streptomyces griseus), most cells remained alive and the induction of enzymes of the phenylpropanoid pathway lasted for several days, resulting in an accumulation of cinnamoyltyramines in the cells and in the culture medium. Treatment with pronase induced an increase in the activity of moderately anionic isoperoxidases which were also induced in pectinase‐treated cells. Cinnamyl alcohol dehydrogenase activity remained stable in pronase‐elicited cells, which rapidly accumulated thioglycolic acid‐extractable phenolic polymers in their cell walls. The accumulation of these polymers coincided with the induction of 4‐coumarate:CoA ligase but preceded the rise in tyramine hydroxycinnamoyltransferase and peroxidase activities.
Controlled mycorrhizal initiation as a means to improve root development in somatic embryo plantlets of hybrid larch (Larix × eurolepis)
Authors: Piola F. , Rohr R. , von Aderkas P.
Published: May 2006

This study represents the first report of in vitro mycorrhization of somatic embryo‐derived plantlets. Effects of fungi on the rooting of plantlets as well as on their ultra‐structure were studied. Embryo‐derived plantlets of a hybrid larch (Larix × eurolepis Henry) were grown aseptically in the presence of four ectomycorrhizal fungi. One month after inoculation with Laccaria laccata, Hebeloma cylindrosporum and Pisolithus tinctorius, the number of plantlets which had developed a well‐growing root system was significantly improved compared with controls. Furthermore, root branching was strongly stimulated by L. laccata and H. cylindrosporum, which were more efficient species than P. tinctorius and Suillus grevillei. Development of the root system was concomitantly accompanied by an enhancement of shoot growth, except for plantlets inoculated with S. grevillei, which died after three to six months. At the ultrastructural level, cross‐sections of lateral roots made six months after inoculation, showed the presence of a Hartig net in the case of L. laccata and H. cylindrosporum, whereas no such net was observed with the two other fungi. With S. grevillei, some perforating hyphae penetrated the cortical cells and resulted in cell death. Evidence of a relationship between structure and efficiency of the association was found.
Persistent effects of low concentrations of SO2 and NO2 on photosynthesis in Scots pine (Pinus sylvestris) needles
Authors: Strand Martin
Published: May 2006

In an open‐field experiment, 50‐year‐old trees of Scots pine (Pinus sylvestris L.) were fumigated with low concentrations of SO2 and NO2 (10–15 nl I−1) during the growing season in four consecutive years (1988 to 1991). Results from the autumn and early winter of 1991 and 1992 are presented. The maximum photochemical efficiency of photosystem II (PSII), as indicated by the ratio of variable to maximum fluorescence (Fv/FM) was assessed in current and one‐year‐old needles from the top and the bottom of the canopy. Furthermore, simultaneous measurements of photosynthetic O2 evolution and chlorophyll fluorescence were made in current‐year needles at 20°C. In general, the Fv/FM ratio as well as the gross rate of O2 evolution in needles of fumigated trees was not significantly different from that in needles of control trees during the fumigation period. However, both current and one‐year‐old needles sampled in November and December 1991 from the top of the canopy of fumigated trees had significantly lower Fv/FM values than corresponding needles of control trees. Similar differences in Fv/FM correlated with the treatments were observed in needles from the bottom of the canopy, indicating that the depression of Fv/FM in needles of fumigated trees was not due to an increased susceptibility to photoinhibition. In 1992, when no fumigation occurred, differences in Fv/FM between the treatments were not significant during autumn and early winter. The gross rate of O2 evolution at high irradiances was significantly lower in current‐year needles of fumigated trees sampled in November and December 1991 than in those of control trees. Furthermore, a nearly identical linear relationship between the quantum yield of PSII electron transport determined from chlorophyll fluorescence and the quantum yield of O2 evolution (gross rate of O2 evolution/PPFD) was found during autumn and early winter. This appeared to be largely a result of changes in the thermal energy dissipation within PSII. The observed differences in photosynthetic characteristics correlated with the different treatments after the fumigation period is suggested to be mainly caused by increased sensitivity of the needles of fumigated trees to low and subfreezing temperatures. However, current‐year needles of fumigated trees tended to have a lower N content than those of control trees, which may partly explain the differences in gross photosynthesis between fumigated and control trees.
Purification and partial characterization of a protease associated with photosystem II particles
Authors: Zhang Li‐Xin , Wang Jun , Wen Jiang‐Qi , Liang Hou‐Guo , Du Lin‐Fang
Published: May 2006

A protease was extracted with 1 M NaCl from spinach (Spinacia oleracea L.) photosystem II (PSII) particles and purified through gel filtration and anion‐exchange chromatography. SDS‐polyacrylamide gel electrophoresis of the protease revealed a polypeptide with a molecular mass of 43 kDa. The activity of the purified protease was assayed using a 24 kDa water‐soluble protein as substrate, visualized through SDS‐PAGE. The protease even remained active in the presence of 0.1 and 0.2 M NaCl, although the degradation pattern changed, which indicated that the protease was different from that reported earlier by another group. The presence of 0.3 M NaCl was shown to be inhibitory. The protease was inhibited by 1,10‐phenanthroline and EGTA‐NaOH (pH 7.0), indicating that the metal ions are essential for activity and that the enzyme is a metal‐protease. FTIR spectroscopy was used to examine the conformationally sensitive amide I' bands of the protease. The protease was observed to undergo spectroscopic changes that reflect the conformational changes that take place when Ca2+ is bound, which further confirms that the protease is a metal‐protease.
Sulfhydryl groups in root‐cell plasma membranes of wheat genotypes differing in Zn efficiency
Authors: Rengel Zdenko
Published: May 2006

Sulfhydryl groups were quantified in root‐cell plasma membranes of two genotypes of wheat (Triticum aestivum cv. Warigal and T. turgidum conv. durum cv. Durati) differing in Zn efficiency. Smaller amounts of 5,5′‐dithio‐bis(2‐nitrobenzoic acid)‐reactive sulfhydryl groups were found in Zn‐deficient than in Zn‐sufficient roots; and also in Zn‐inefficient genotype Durati compared to Zn‐efficient Warigal, regardless of Zn supply. Upon transfer of 15‐day‐old Zn‐deficient plants into solutions containing various Zn2+ activities, a Zn‐dependent increase in the amount of reactive sulfhydryl groups was evident in roots of both genotypes, but occurred only in Warigal when 20‐day‐old plants were used, indicating irreversible physiological damage in Durati plants due to prolonged Zn deficiency. Upon transfer into solutions of increasing Zn2+ activities, the increase in total Zn concentration in roots was about an order of magnitude smaller than the increase in amounts of reactive sulfhydryl groups in the roots of both genotypes, suggesting that, in wheat roots, a relatively small amount of Zn is required for preventing oxidation of sulfhydryl groups into disulfides. The amount of reactive sulfhydryl groups in the roots is positively related to Zn efficiency of wheat genotypes and may be one of the mechanisms that, under conditions of Zn deficiency, allow better growth and productivity of Zn‐efficient genotypes in comparison to Zninefficient ones.
Abscisic acid increases in non‐growing and paclobutrazol‐treated fruits of seedless mandarins
Authors: Zacarias L. , Talon M. , Ben‐Cheikh W. , Lafuente M. T. , Primo‐Millo E.
Published: May 2006

Clementine (Citrus reticulata [Hort.] Ex. Tanaka cv. Oroval) is a self‐incompatible mandarin with a slow rate of fruit growth and high percentage of fruit abscission. Seedless Satsuma (Citrus unshiu [Mak] Marc. cv. Clausellina) shows natural parthenocarpy and higher fruit set. Application of 25 μg fruit−1 of paclobutrazol (PP333), an inhibitor of gibberellin biosynthesis, reduced the rate of growth and accelerated fruit abscission in both varieties. In contrast, gibberellin A3 (GA3) stimulated fruit growth only in the self‐incompatible mandarin. Clementine fruits, in the absence of pollination, showed an approximately 2‐fold transient increase in the free abscisic acid (ABA) content shortly after petal fall. In Satsuma, a very small accumulation of ABA was detected. Paclobutrazol treatment induced a 3‐fold increase in ABA in Satsuma fruits but did not substantially affect the pattern of ABA accumulation in Clementine. In this variety, GA3 suppressed the ABA increase observed in untreated fruits. These effects were observed 24 h after treatment. However, in Satsuma fruits, the effect of GA3 on the ABA content was negligible. In addition, a comparative analysis of growing and non‐growing fruits of Clementine showed that ABA, on a per unit weight basis, was always higher in the non‐growing fruits. Treatment with 85 μM fluridone, an inhibitor of carotenoid biosynthesis and thus indirectly of ABA, delayed fruit abscission in Clementine, but also decreased fruit growth. Collectively, these observations indicate a relationship between high ABA content and a reduced rate of fruit growth and an acceleration of fruit abscission.
Osmotin gene expression is controlled by elicitor synergism
Authors: Chang Pi‐Fang Linda , Cheah Kheng T. , Narasimhan Meena L. , Hasegawa Paul M. , Bressan Ray A.
Published: May 2006

Arachidonic acid (AA), a fatty‐acid fungal elicitor, and a cellulase preparation from Aspergillus niger, a protein‐type fungal elicitor, induced osmotin gene expression. Both elicitors activated the osmotin promoter fused to a β‐glucuronidase (GUS) reporter gene in a tissue‐specific manner in tobacco seedlings (Nicotiana tabacum L. cv. Wisconsin 38). The cellulase preparation was more effective than AA at the concentrations tested and, unlike AA, also induced the accumulation of osmotin mRNA and protein. Combinations of AA and the cellulase preparation had a greater than additive effect on the activation of the osmotin promoter and the accumulation of osmotin mRNA and protein. Both AA and the cellulase preparation, when applied separately, were virtually ineffective in the induction of the osmotin promoter in cotyledon tissues. However, together they were able to induce synergistically GUS fused to the osmotin promoter. Increases in osmotin‐promoter‐driven GUS activity and accumulation of osmotin mRNA induced by AA, the cellulase preparation or their combination were reversed by norbornadiene, an ethylene action inhibitor, indicating that ethylene is involved in the induction of the osmotin gene by these elicitors.
Interaction between poly(L‐lysine) and membranes inhibits proton pumping by corn root tonoplast H+‐ATPase
Authors: Tu Shu‐l , Patterson Deidre , Brauer David , Cooke Peter , Sweeney Irma , Hsu An‐Fei
Published: May 2006

The influence of poly(L‐lysine) binding on the coupled activities of nitrate‐sensitive H+‐ATPase in isolated corn (Zea mays L. cv. FRB73) root tonoplast vesicles was investigated. The addition of membrane‐impermeable poly(L‐lysine) caused a slow increase in light scattering of the tonoplast suspension. Electron microscopy showed that the increase was the result of an aggregation of the vesicles. In the presence of 75 mM KCl, a concentration sufficient to sustain near optimal ATP hydrolysis, poly(L‐lysine) slightly enhanced the hydrolysis activity but significantly inhibited proton pumping of the H+‐ATPase. Inhibition increased with the average molecular mass of poly(L‐lysine) and reached a maximum at 58 kDa. When total osmolarity was kept constant, the replacement of sucrose by KCl enhanced both ATP hydrolysis and proton pumping activities. However, enhancement of proton pumping was significantly greater than that of ATP hydrolysis. An increase in KCl, but not K2SO4, significantly relieved poly(L‐lysine)‐induced inhibition of proton pumping. Kinetic analysis indicated that poly(L‐lysine) did not significantly affect the proton leakage of the tonoplast membranes under different energetic conditions. These results suggest that the electrostatic interaction between poly(L‐lysine) and the negative charges on the exterior surface of tonoplast vesicles could change the coupling ratio of ATP hydrolysis to proton pumping. Thus, the surface charge of the tonoplast membrane may be involved in the regulation of these two activities.
Statcking and separatio of photosystem I and photosystem II in plant thylak oid membranes: A physico‐chemical view
Authors: Stys Dalibor
Published: May 2006

The main objective of this article is to highlight important experimental findings and discuss current theories on photosystem segregation and stacking in thylakoid membranes. The facts are put in a framework of recent theoretical developments in the field of membrane biochemistry and biophysics. Some important experiments not considered by the currently accepted theories are discussed. Modifications of these theories in order to incorporate new results are proposed. The currently accepted theories on formation of membrane domains (probably responsible for segregation of photosystem 1 and II) and on interlamellar interactions (stacking) are discussed. Finally, a scheme is put forward summarising the forces which are responsible for organisation of functional structure of thylakoid membranes.
Interaction of jasmonic and abscisic acid in the control of lipases and proteases in germinating apple embryos
Authors: Ranjan Rajiv , Lewak Stanistaw
Published: May 2006

Effects of jasmonic (JA) and abscisic (ABA) acid on the activities of lipases and proteases were studied in cultured embryos excised from apple seeds. JA stimulated alkaline (AlkL) and acid (AcL) lipases as well as proteases hydrolyzing casein, L‐cystine‐di‐β‐naphthylamide (CysβNa), glycyl‐glycyl‐glycine (GlyGlyGly) and native apple seed proteins. ABA inhibited AlkL and protease activities, with the exception of the hydrolysis of native proteins which was stimulated. The activity of AcL was not affected by ABA. AlkL was affected by JA and ABA also in vitro. An antagonistic interaction between JA and ABA on all studied enzyme activities. except CysβNa hydrolyzing protease, was observed. The positions of JA‐ and ABA‐controlled sites in the metabolic regulation of the removal of embryonal dormancy in apple seeds are discussed.
Causes and location of non‐specific effects of SHAM on O2 uptake by wheat roots
Authors: Bingham I. J. , Stevenson E. A.
Published: May 2006

Uptake of O2 by whole, detached, root systems of wheat (Triticum aestivum L. cv. Alexandria) was titrated with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. The resulting Qall plot was non‐linear indicating that SHAM was acting non‐specifically. The nature of the non‐specific effects was investigated in reverse titration experiments. Uptake of O2 was titrated with KCN in the presence and absence of SHAM at 1 mM and 25 mM, which yielded Qcy1 values of < 1 and > 1, respectively. The results suggest that at 25 mM, SHAM inhibits the cytochrome pathway, but at 1 mM it stimulates an O2‐consuming process which is likely to be a peroxidase. A SHAM‐stimulated peroxidase could easily be washed from these roots. In vitro, the peroxidase was stimulated to a similar extent by low (1 mM) and high (25 mM) concentrations of SHAM. Failure to inhibit with high concentrations of SHAM distinguishes this peroxidase from those bitherto eluted from root tissue. Reverse titration experiments in the presence and absence of 1 mM SHAM indicated that there were no significant side effects of SHAM in root tips. These data are supported by the negligible peroxidase activity that was washed from this root fraction. In contrast, significant side effects occurred in vivo, and substantial peroxidase activity was measured in vitro, from sections 4–6 cm and 18–20 cm behind the seminal root apex. The greatest activity was found with the 4–6 cm section which may be associated with high rates of cell wall lignification. The implications of these results for measurements of root respiration are discussed.
Chlorophyll turnover in etiolated greening barley transferred to darkness: Isotopic (1‐14C glutamic acid) evidence of dark chlorophyll synthesis in the absence of chlorophyll accumulation
Authors: Walmsley Jane , Adamson Heather
Published: May 2006

Synthesis of chlorophyll was initiated in 5‐ to 6‐day‐old dark‐grown barley (Hordeum vulgare L. cv. Clipper)seedlings by exposing them to light in the presence of 1‐14 C glutamic acid supplied via the roots.The plants were then returned to darkness. At the end of light treatment (T) and after 7 or 18 h dark treatment chlorophylls a and b were extracted, quantified (μgleaf1). purified by HPLC to their magnesium‐free derivatives (pheophytin a and b) and their molar radioactivities determined. After 2 h exposure to light followed by 6 h illumination in the presence of 1‐14 C glutamic acid, seedlings had accumulated 4‐7 nmol chlorophyll leaf1 and had incorporated between 900‐1 350 Bq (g fresh weight)1 of radioactive label into the chlorophyll pool. When seedlings were transferred to darkness, label continued to be incorporated and after 18 h the radioactivity of the chlorophyll pool had increased by 300‐700 Bq (g fresh weight)1. Net chlorophyll content, however, remained constant during dark treatment. The increase in radioactivity of the chlorophyll pool in darkness represented the difference between a net increase of label incorporated into chlorophyll a and a small loss of label from chlorophyll b. The absence of measurable radioactivity in the phytol moiety of labelled chlorophyll a, extracted at the endof dark treatment, demonstrated thatincorporation of label was into the tetrapyrrole moiely of chlorophyll and not into the phytol chain. Light‐independent incorporation of 1‐14 C glutamic acid into chlorophyll of greening barley seedlings transferred to darkness indicates that chlorophyll synthesis continues when light is withheld. We interpret the net gain in radioactivity of chlorophyll in darkness, in the absence of a net gain in chlorophyll content, to chlorophyll turnover i.e. to simultaneous synthesis and breakdown of chlorophyll when etiolated greening barley seedlings are transferred to darkness.