bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of native and solubilized plasma membrane ATPase from the halophyte Plantago crassifolia, grown under saline and non‐saline conditions
Authors: Brüggemann Wolfgang , Janiesch Peter
Published: May 2006

Plasma membrane ATPase from the mediterranean halophyte Plantago crassifolia Forskal was analysed in the native and solubilized state. The enzyme revealed a broad pH optimum at 6.3 when analysed in plasma membrane preparations from roots. A further purified preparation of leaf plasma membrane ATPase was obtained by a three‐step solubilization method. Final solubilization of the enzyme was achieved with 1% lysophosphatidylcholine. This enzyme showed a narrow pH optimum at 6.3, inhibition by vanadate, fluoride and N,N′‐dicyclohexylcarbodiimide and a high specificity for ATP. The preparations contained a major polypeptide of 107 kDa. None of the parameters analysed in this enzyme changed upon transfer to saline conditions, although the leaves accumulated Na+ and Cl− and an enhanced formation of the compatible organic osmoticum, sorbitol, was detected. It is concluded that at least in this halophyte, the plasma membrane ATPase undergoes no changes during the physiological adaptation of the plant to a saline environment.
Net CO2 exchange of Pinus taeda shoots exposed to variable ozone levels and rain chemistries in field and laboratory settings
Authors: Hanson Paul J. , McLaughlin Samuel B. , Edwards Nelson T.
Published: May 2006

Net CO2 exchange rates (CERs) were measured in seedlings of two loblotly pine (Pinus taeda L.) families following 6‐ or 13‐week exposures to ozone (charcoalfiltered or ambient air + O3) and acid rain treatments (pH 3.3, 4.5 and 5.2). Ozone exposures (14 or 170 nl l−1) were made in open‐top chambers, and in continously stirred tank reactors (14, 160 or 320 nl l−1) located in the field and laboratory, respectively. The CERs of whole shoots were measured in an open infrared gas analysis system at 6 levels of photosynthetic photon flux density (0, 33, 60, 410, 800 and 1660 μmol m−2 s−1). Treatment effects were not consistent between field‐ and laboratory‐exposed seedlings. Ozone‐treated field seedlings exhibited statistically significant reductions in light‐saturated CER of 12.5 and 25% when measured at 6 and 13 weeks, respectively. Laboratory seedlings exhibited mixed responses to O3, with one family showing reduced CER only after 6 weeks of O3 exposure and the other only after 13 weeks (O3 >160 nl l−1 for both). After 13 weeks of exposure, pH 3.3, and 4.5 rain treatments enhanced light‐saturated CER by an average of 52% over that observed in seedlings exposed to the pH 5.2 treatment. Enhanced CERs due to acid rain were of the same magnitude (3–5 μmol CO2g−1 s−1) as ozone‐induced CER reductions. No differences in dark respiration were detected between treatments. Although ozone and acid rain treatments altered seedling CER, the differences were not translated into altered final plant dry weights over the 13‐week exposure period.
Chloride and sulphur concentrations in chloroplasts of spinach
Authors: Van Steveninck Reinhard F.M. , Fernando Denise R. , Anderson Christopher A. , Edwards Linton B. , Van Steveninck Margaret E.
Published: May 2006

Chloride concentrations within individual chloroplasts, the adjacent cytoplasm and nearby vacuoles of spinach mesophyll cells (Spinacea oleracea L. cv. Hybrid 102) were determined by means of electron probe X‐ray microanalysis in the cleavage plane of quench frozen tissue, which was maintained at liquid nitrogen temperatures. The accuracy of quantitative data obtained with this technique is greatly improved by the adoption of a peak to background ratio method and use of carbon slurry standards, which mimic the quench frozen tissue and its X‐ray fluorescence.

Chloroplasts were incapable of maintaining relatively high levels of Cl− under conditions of low Cl− availability (zero Cl− or 20 μM Cl− in nutrient solution), and under conditions of Cl− stress (100 or 200 mM Cl−) chloroplasts had only a limited capacity to maintain a Cl− concentration at a level below that of the cytoplasm and vacuole. However, under conditions of Cl− stress the concentration of Cl− in cytoplasm immediately adjacent to chloroplasts was substantially higher than in the chloroplasts or more distant cytoplasm. Thus, Cl− levels in chloroplasts are apparently not as tightly regulated as was suggested by estimates of Cl− concentration based on aqueous isolation of chloroplasts.

Levels of S in chloroplasts were relatively high (equivalent to 40–60 mM SO42− in S standards) and constant for all treatments, with the possible exception of lower S levels in chloroplasts of leaves approaching premature senescence as a result of salt stress. It is implied that the stability of the S‐content results largely from its presence in macromolecular components of chloroplasts (sulfolipids and proteins).
Relationship between water content and afterripening in red rice
Authors: Leopold A. C. , Glenister R. , Cohn M. A.
Published: May 2006

Reactions regulating seed dormancy can proceed at water contents which are probably too low to permit metabolic activity. The loss of dormancy via afterripening of red rice. (Oryza sativa L.) seeds was examined as a representative case. Equilibration of seeds to various moisture contents showed that afterripening was most rapid at 6–14% moisture content (dry weight basis). Afterripening did not occur at > 18% moisture content and was severely inhibited at < 5% moisture content. Seed viability was greater than 95% for all treatments. Utilization of moisture isotherms to calculate water‐binding enthalpy values identified the optimal afterripening range as approximately the boundary between water‐binding region 1 and region 2. From these findings, it is suggested that afterripening may involve some oxidative reactions which are inhibited at lower water contents by the rising free‐energy and at the higher side by metabolic reactions.
Cysteine, γ‐glutamyl‐cysteine and glutathione contents of spinach leaves as affected by darkness and application of excess sulfur
Authors: Buwalda F. , de Kok L. J. , Stulen I. , Kuiper P. J. C.
Published: May 2006

In the light, glutathione was the major water‐soluble, non‐protein, sulfhydryl compound in leaves of spinach (Spinacia oleracea L. cv. Estivato). In the dark, another sulfhydryl compound accumulated, which proved to be γ‐glutamyl‐cysteine. In the light, exposure of leaves to excess sulfur in the form of atmospheric H2S (0.25 μl l−1) resulted in considerably increased levels of glutathione and cysteine. In the dark, in addition to these thiols, levels of γ‐glutamyl‐cysteine were also enhanced considerably. When leaves of plants exposed to H2S in the dark were illuminated, the dipeptide rapidly disappeared. At the same time, glutathione contents increased by approximately the same amount, indicating a light‐dependent conversion of γ‐glutamyl‐cysteine into glutathione. Possible mechanisms for these light‐induced changes in thiol metabolism are discussed.
Growth and osmoregulation in Pisum sativum subhooks as affected by gibberellic acid and cotyledon excision
Authors: Miyamoto Kensuke , Kamisaka Seiichiro
Published: May 2006

Growth stimulation by gibberellic acid (GA) of the Alaska pea (Pisum sativum L.) subhook was observed within 6 h after its application; the stimulation being larger in cuttings with cotyledons than in decotylized ones. The osmotic potential in the subhook increased as it grew, the rate of its increase being faster in cuttings without than in cuttings with cotyledons. GA had no effect on the change in the osmotic potential until 8 h after GA application, but afterwards it suppressed the increase in cuttings with cotyledons. This GA effect was not observed in decotylized cuttings. Changes in the osmotic potential were well correlated with changes in the concentration of soluble sugars, but not with changes in amino acids and K+, Soluble sugars accumulated in the subhook of cuttings with and without cotyledons in proportion to growth, irrespective of the presence or absence of GA. Cotyledon excision suppressed sugar accumulation, and GA promoted it in cuttings with cotyledons but not in decotylized ones. These results suggest that GA stimulates the translocation of sugars from the cotyledons to the subhook and, thereby, maintains the osmotic potential low, resulting in enhanced growth.
Epibrassinolide‐inhibition of development of excised, adventitious and intact roots of tomato (Lycopersicon esculentum): comparison with the effects of steroidal estrogens
Authors: Guan Ming , Roddick James G.
Published: May 2006

The brassinosteroid, 24‐epibrassinolide, caused observable inhibition of the growth of aseptically‐cultured excised tomato (Lycopersicon esculentum Mill. cv. Best of All) roots at a concentration of 0.01 μM. Root formation and outgrowth in tomato shoot cuttings and root biomass in intact tomato seedlings were also depressed by epibrassinolide, but only at a higher concentration (0.1μM). Concentrations of the steroidal estrogens, estrone and estradiol (as sulphate derivatives), in excess of 1.0 μM, reduced cultured root growth as well as root number and total (but not mean) root length in shoot cuttings. Seedling root growth was only slightly inhibited by estradiol but not by estrone. Both epibrassinolide and estrogens caused morphological abnormalities, such as epinasty and leaf‐inrolling in cuttings and seedlings. Epibrassinolide stimulated extension growth of the hypocotyl and epicotyl in cuttings and of the hypocotyl in seedlings, but estrogens exerted no effects on shoot growth.
Properties and localization of the homoglutathione synthetase from Phaseolus coccineus leaves
Authors: Klapheck S. , Zopes H. , Levels H.‐G. , Bergmann L.
Published: May 2006

The synthesis of homoglutathione (hGSH) by several plants of the tribe Phaseoleae is shown to be catalysed by a β‐alanine‐specific hGSH synthetase, Properties of the enzyme from Phaseolus coccineus L. cv. Preisgewinner were studied, using ammonium sulfate precipitates of primary leaf extracts. The hGSH synthetase showed a broad pH optimum at pH 8–9, an absolute requirement for Mg2+, a stimulation by K+, and a high affinity for γ‐glutamylcysteine [Km(app.) 73 μM]. The enzyme exhibited a high specificity for β‐alanine [Km(app.) 1.34 mM] compared to glycine [Km(app.) 98 mM]. Chloroplasts, isolated from the leaves of Phaseolus coccineus, contained about 17% of the hGSH synthetase activity in the leaf cells.
Bacteria‐plant interactions in symbiotic nitrogen fixation
Authors: Quispel A.
Published: May 2006

In the inter‐ and intracellular N2‐fixing symbioses between plants and micro‐symbionts, the development of an endophytic form of the micro‐symbiont is essential. This development includes a series of steps consisting of plant‐bacteria interactions. Considerable progress in the elucidation of these steps has been made by applications of the methods of molecular genetics. Several genes with a role during infection and nodulation have been indicated in Rhizobium and Bradyrhizobium like the common nod genes A, B, C, I and J, and the host‐specific genes nod E, F and H. The nod D gene is the only constitutive gene, and its product is essential for activity of all other nod genes, provided some flavonoids from the root exudate are present as well. Mutants in these genes show phenotypic effects, in which the products of the genes must be involved. Far more difficult is the biochemical and physiological study of these products and their direct effects.

The difficulties involved in such biochemical‐physiological studies is illustrated by a short discussion of the controversies around the possible role of plant lectins. While in Rhizobium the nod genes are present on a large sym‐plasmid, other essential genes must be present on the bacterial chromosome and on other plasmids. Induction of plant genes is evident from the formation of nodule‐specific proteins, the nodulins. Though many different plant and bacterial genes are involved in the series of steps in the development of an effective root nodule, there are indications that regulation is affected by a smaller number of essential regulatory genes. This is illustrated by the effect of the regulatory nod D gene during infection and nodulation, and of ntrA and nifA genes for the formation and activation of the nitrogen‐fixing systems. Moreover, every step, once initiated, may lead to cascade effects on subsequent reactions.

Finally, some further consequences of the endophytic way of life are discussed, which affect either the metabolic and transport activities of the endophytes or their viability. This is illustrated by the possible role of membrane integrity as evident during the isolation of Frankia from its endophytic form.
Modulation of plasma membrane H+‐ATPase from oat roots by lysophosphatidylcholine, free fatty acids and phospholipase A2
Authors: Palmgren Michael Gjedde , Sommarin Marianne , Ulvlskov Peter , Jørgensen Peter Leth
Published: May 2006

Plasma membrane vesicles were purified from 8‐day‐old oat (Avena sativa L. cv. Brighton) roots in an aqueous polymer two‐phase system. The plasma membranes possessed high specific ATPase activity [ca 4 μmol P1 (mg protein)−1 min−1 at 37°C]. Addition of lysophosphatidylcholine (lyso‐PC) produced a 2–3 fold activation of the plasma membrane ATPase, an effect due both to exposure of latent ATP binding sites and to a true activation of the enzyme. Lipid activation increased the affinity for ATP and caused a shift of the pH optimum of the H+ ‐ATPase activity to 6.75 as compared to pH 6.45 for the negative H+‐ATPase. Activation was dependent on the chain length of the acyl group of the lyso‐PC, with maximal activition obtained by palmitoyl lyso‐PC. Free fatty acids also activated the membrane‐bound H+‐ATPase. This activation was also dependent on chain length and to the degree of unsaturation, with linolenic and arachidonic acid as the most efficient fatty acids. Exogenously added PC was hydrolyzed to lyso‐PC and free fatty acids by an enzyme in the plasma membrane preparation, presumably of the phospholipase A type. Both lyso‐PC and free fatty acids are products of phospholipase A2 (EC 3.1.1.4) action, and addition of phospholipase A2 from animal sources increased the H+‐ATPase activity within seconds. Interaction with lipids and fatty acids could thus be part of the regulatory system for H+‐ATPase activity in vivo, and the endogenous phospholipase may be involved in the regulation of the H+‐ATPase activity in the plasma membranne.
Inorganic nitrogen assimilation in plants of Austrlian rainforest communities
Authors: Stewart G. R. , Hegarty E. E. , Specht R. L.
Published: May 2006

In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase (EC 1.6.6.1) and were predominantly leaf nitrate assimilators. Under‐ and over‐storey species had low levels of shoot and root nitrate reductase activity, and many of them showed little capacity for nitrate reduction even when nitrate ions were freely available. Although closed‐forest species have lower levels of nitrate reductase than those of gaps and forest margins, their total nitrogen contents were similar, suggesting the former utilize nitrogen sources other than nitrate ions. Glutamine synthetase (EC 6.3.1.2) was present in the leaves of all species examined. In the leaves of pioneer species the chloroplastic isoform of glutamine synthetase predominted, while in most of the species typical of closed‐forest the cytosolic isoform accounted for at least 40% of total leaf activity. Low levels of chloroplastic glutamine synthetase were correlated with a low capacity for leaf nitrate reduction, and both are characteristic of many species that regenerate and grow for some time in shade. Low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re‐assimilated via cytosolic glutamine synthetase.
Calcium regulation of exogenous and endogenous 1‐aminocylopropane‐1‐carboxylic acid bioconversion to ethylene
Authors: Cheverry J. L. , Pouliquen J. , Le Guyader H. , Marcellin P.
Published: May 2006

Ethylene production and overall levels of free and conjugated 1‐aminocyclopropane‐1‐carboxylic acid (ACC) were studied in parenchymatous tissues, excised from clmacteric apples (Malus domestica Borkh. cv. Granny Smith) and infiltrated with an incubation medium containing 0, 1, 10 or 100 mM Ca2+, with or without exogenous ACC (2 mM). Irrespective of whether exogenous ACC was applied or not, ethylene production was inhibited to the same extent (40%) by an apoplastic effect of 100 mM Ca2+. In the absence of external ACC, the inhibition was associated with an increase in total endogenous ACC and may be related to a reduction in the rate of the last step of ethylene pathway. This suggests that the ethylene‐forming enzyme (EFE) is localized in the plasma membrane. Low Ca2+ concentrations (1 mM) enhanced basal ethylene synthesis due to influx of Ca2+ into the cytosol, while overall concentrations of ACC in the tissue decreased. However, 1 mM Ca2+ did not stimulate ACC‐dependent ethylene formation. Thus, Ca2+ influx may stimulate the translocation of endogenous ACC from synthesis or storage compartment (s) to reactive site(s) of the plasma membrane. The concentration of 10 mM Ca2+ had no effect on basal ethylene production and appears to represent a balance point between the stimulating and inhibiting effects of 1 and 100 mM Ca2+, respectively, Furthermore, the charge‐times of exogenous ACC observed with 0, 1 and 10 mM Ca2+ suggest that EFE is located on the inner side of the plasma membrane.
Import of sucrose and its transformation to starch in the developing sorghum caryopsis
Authors: Singh Rangil , Asthir Bavita
Published: May 2006

Levels of soluble and bound invertases and amylases were studied in relation to the changes in the free sugars and the accumulation of starch in the developing sorghum [Sorghum bicolor (L.) Moench, cv. spv. 351] caryopsis and its associated bractspedicel. Besides sucrose, glucose and fructose as the principal sugars, small amounts of sugars of the raffinose series were detected in the developing caryopsis. Through out the period of caryopsis development, the amount of reducing sugars was higher than that of sucrose. With the advancement in the development of the caryopsis, the contents and levels of sucrose rose with a concomitant fall in the activity of soluble acid (pH 4.8) invertase (EC 3.2.1.26) in the endosperm. In the pericarp‐aleurone layer, the activity of soluble acid invertase predominated over soluble neutral (pH 7.5) invertase (EC 3.2.1.27). The activity of bound acid invertase declined with the ageing of the caryopsis. In bracts‐pedicel, the activity of bound invertase and the levels of reducing sugars peaked around 18 days post anthesis. In these organs, the level of starch gradually decreased concomitantly with an increase in its level in the developing caryopsis. Amylases (EC 3.2.1.1 and 3.2.1.2) are distributed in the endosperm as well as in the pericarp‐aleurone layer. On culturing detached ears in [U‐14C]‐sucrose solution for 6 h in the dark at 25°C, 80–90% of the 14C of extracted major sugars (i.e. sucrose + glucose + fructose) of the caryopsis appeared in sucrose alone. In comparison with the effects of glucose or fructose, transport into the caryopsis of 14C from [U‐14C]‐sucrose supplied to detached ears was promoted by the addition to the radiolabelled sucrose solution of 1% unlabelled sucrose. Addition to the [U‐14C]‐sucrose solution fed to the detached ears of 20 mM NaN3 or HgCl2 or galactose, lowered the amount of 14C in the free sugars and starch of the earyopsis.
Nitrogenase activity and ureide levels in a supernodulating soybean mutant: Effects of inoculum dose and nitrate treatment
Authors: Schuller Kathryn A. , Day David A. , Gresshoff Peter M.
Published: May 2006

The effects of nitrate on nitrogenase (EC 1.18.2.1) activity of soybean (Glycine max [L.] Merr) cv. Bragg and its supernodulating mutant derivative, nts382, were compared. A short‐term nitrate treatment was used to allow effects on nitrogenase activity to be studied in the absence of effects on nodule growth and a low inoculum dose, which prevented supernodulation of nts382, was employed to test for any interaction between supernodulation and the magnitude of the effect of nitrate on nitrogenase activity. At the usual inoculum dose, nitrogenase activity, per g nocule, of nts382 was lower than that of Bragg and was proportionally less affected by nitrate. Decreasing the inoculum dose increased nitrogenase activity of nts382 and also the proportional decline in response to nitrate. The decline in the ureide conentration in xylem exudate in response to nitrate was proportionally similar to the decline in nitrogenase activity per plant. However, although nitrogenase activity per plant of nts382 was several‐fold less than that of Bragg, the ureide flux rate (ureide concentration x xylem sap exudation rate), was not different. At the usual inodulum dose, the ureide content of the nocules, stems plus petioles and leaves of nts382 was greater than that of Bragg. Decreasing the inoculum dose reduced the ureide content of the nodules of nts382 but not of Bragg. Ureide degradative capacity of the leaves was the same for Bragg and nts382. Low activities of 5‐phosphoribosyl pyrophosphate amidotransferase (EC 2.4.2.14) and glutamine synthetase (EC 6.3.1.2) in the nodules reflected the low nitrogenase activity of nts382.
Effects of age, supra‐ambient oxygen and repeated assays on acetylene reduction and root respiration in pea
Authors: Rosendahl Lis , Jakobsen Iver
Published: May 2006

An open flow‐through gas system was used to investigate the effect of plant age on nitrogenase activity in relation to root respiration (measured as CO2 release) and supra‐ambient O2 levels in 24‐ to 51‐day‐old, nodulated Pisum sativum L. cv. Bodil. The effect of assaying plants repeatedly was also studied. The respiratory efficiency of nitrogenase [mol CO2 (mol C2H4)−1] and the relative decline in nitrogenase (EC 1.7.99.2) activity in response to introduction of C2H2 in the gas stream were unaffected by plant age. In contrast, the nitrogenase‐linked respiration as a proportion of total root respiration increased with time. Accordingly, the specific respiration linked‐to growth and maintenace of the noduled root system decreased with time. C2H2 reduction and root respiration were increased by supra‐ambient O2 levels, but the tolerance to high O2 concentrations seemed to decrease with plant age. Repeated C2H2 assays on the same plants decreased their rate of growth and N accumulation: in addition, nitrogenase activity and root respiration were somewhat negatively affected. The results indicate that results from experiments with plants of different ages cannot always be directly compared, and that repeated C2H2 assays on the same plants should be applied with caution in physiological work.
Internode length in Pisum. Comparison of genotypes in the light and dark
Authors: Reid James B.
Published: May 2006

There is a strong relationship across the full range of gibberellin deficient, internode length genotypes (le, lh, is, na) between internode length in the dark and in red or white light. Further, the new, more severe allele at the le locus. Ied, is shown to influence growth in the dark as well as in the light. These results suggest that darkeness does not specifically overcome any of the steps blocked by the gibberellin (GA) synthesis genes contrasting with the conclusions drawn by other workers. Supporting this conclusion in relation to the Ie gene are results which show that, at least at certain dosage rates, dark‐grown Ie na plants respond better to GA1 than to GA20 similar to the response previously reported in light grown plants.

The greater response by plants of the nana line NGB1766 (na) to GA1 in the dark than in the light suggests that light may influence internode length by altering GA‐sensitivity. These results are discussed in relation to previous views on the control of stem elongation by light.
Effects of elevated oxygen tensions on acetylene reduction inAlnus incana‐Frankiasymbioses
Authors: Rosendahl Lis , Huss‐Danell Kerstin
Published: May 2006

An open flow‐through gas system was used to determine the effect of C2H2and elevated O2on acetylene reduction activity (ARA) and respiration of the intact, potted root system ofAlnus incana(L.) Moench in symbiosis withFrankiaAvcll or with a local source ofFrankia. Both symbiotic systems responded to C2H2by an immediate plateau range in ARA. The Plateau in ARA was in some cases followed by a decline of less extent than reported for many legumes. A concurrent decline in net respiration of the root system was on average 8% of the CO2efflux prior to C2H2introduction.

Respiration of the root systems in both symbioses responded to elevated oxygen levels in the 10 kPa C2H2atmosphere by an increase of up to 17% of the net respiration prior to C2H2introduction in 21 kPa O2. In contrast, the elevated oxygen levels resulted in an immediate drop in ARA followed by a minor increase to a stable level lower than that at the preceding, lower oxygen tension. The symbiosis with the localFrankiahad lost all ARA when the partial pressure of O2exceeded 50 kPa, whereas the symbiosis with Avcll still had some activity at 80 kPa O2. This difference in tolerance of elevated O2clearly shows that the oxygen exclusion mechanisms may be controlled by the microsymbiont inAlnus‐Frankiasymbioses. The symbiotic systems recovered ARA to a similar extent when returned from elevated O2levels to 21 kPa O2.
C and N utilization of two lettuce genotypes during growth under non‐varying light conditions and after changing the light intensity
Authors: Blom‐Zandstra Margaretha , Lampe Jan E. M. , Ammerlaan Fracina H. M.
Published: May 2006

Growth and N‐incorporation in two lettuce genotypes (Lactuca sativa L. cv. Deci minor and cv. Grosse brune), which differ significantly in nitrate accumulation, were studied. Under constant environmental conditions cv. Deci minor produced more fresh and dry weight than cv. Grosse brune. Cultivar Deci minor also produced more fresh weight per mmol N absorbed than cv. Grosse brune, and contained less organic nitrogen in the dry matter, but accumulated more nitrate. As cv. Deci minor showed a higher fresh and dry weight production per mmol N absorbed than cv. Grosse brune, it used its nitrogen more efficiently.

When the light intensity was decreased, the growth of both cultivars decreased, and the fresh weight production per mmol N absorbed increased. After reduction of the light intensity, cv. Deci minor maintained a higher fresh weight production per N absorbed than before, whereas cv. Grosse brune returned to its original level. After decrease of the light intensity, an increased nitrate concentration in the cell sap was accompanied by a decreased concentration of organic compounds in both cultivars. The organic nitrogen level in the dry matter remained constant after the higher intensity was reduced. However, due to the decreased dry weight percentage, the demand for nitrogen for protein synthesis decreased on fresh weight basis.

It can be concluded that the two cultivars differ in their partition of C and N between dry matter and cell sap. Nitrate accumulation in preference to accumulation of organic compounds does not automatically result from a shortage of organic compounds. The high accumulation of nitrate of cv. Deci minor enables it to use more carbohydrates for structural growth than cv. Grosse brune.
Interaction of potassium ions and gibberellin in the control of hypocotyl growth in Amaranthus caudatus
Authors: Guruprasad Anita , Guruprasad K. N.
Published: May 2006

Potassium promotes growth in several plant tissues. Elongation growth of the hypocotyls of Amaranthus caudatus L. ev. Lalsag is mainly controlled by gibberellins, but K+ also promotes growth. In the present study the interaction of K+ with gibberellin (GA3) and chlorocholine chloride (CCC) has been investigated. When K+ was applied externally in the dark, hypocotyl growth was promoted in the seedlings. External application of GA3 did not promote growth in the dark. GA3 was effective in the light and K+ was synergistic with GA3 in promoting elongation. Application of CCC in the dark makes the seedlings sensitive to GA3. The inhibition of growth by CCC was also reversed by K+. The results indicate a possible role of K+ in GA3 induced elongation of hypocotyls.
Molecular and serological comparisons of purified xanthine dehydrogenases from root nodules of three ureide‐producing legume species
Authors: Triplett Eric W. , Hao Amy C.
Published: May 2006

Xanthine dehydrogenase (XDH, EC 1.2.1.37) was immunopurified from root nodules of three legume species, soybean [Glycine max (L.) Merr. cv. Pella], cowpea [Vigna unguiculata (L.) Walp. cv. California Black Eye], and lima bean [Phaseolus lunatus L. Henderson]. Polyclonal antibodies raised against each enzyme and monoclonal antibodies raised against soybean XDH were used to compare the three enzymes serologically. Double diffusion and enzyme‐linked immunosorbent assays with polyclonal and monoclonal antibodies showed that the cowpea and lima bean enzymes are very similar immunologically but both differ measurably from soybean. Amino acid compositions of the legume nodule XDHs are presented as well. Although relatedness between these enzymes can be detected by immunological crossreactivity, each XDH has unique epitopes that can be used to distinguish the three proteins.
Glutamine synthetase activity of the endosperm, embryo and pedicel‐placento‐chalazal regions of developing maize (Zea mays) kernels
Authors: Muhitch Michael J.
Published: May 2006

Glutamine synthetase (GS, EC 6.3.1.2) activity in homogenates of the maize (Zea mays L. hybrid A619 X W64A) kernel pedicel‐placento‐chalazal (PPCh), endosperm regions was characterized in order to optimize assay (hydroxylamine‐dependent γ‐glutamyl hydroxymate formation) conditions for quantitating maize kernel GS in crude extracts. The GS activities of all three tissue extracts exhibited optima at pH 7.0 with ATP:Mg2+ of 1:1.6. Assays of kernel tissue GS activity required relatively high concentrations of substrates to achieve saturation compared to GS from other plant tissue sources, a point which has not been considered in previous reports of maize kernel GS activity. When measured under optimal assay conditions. PPCh‐GS increased to a peak of 51 nmol γ‐glutamyl hydroxymate kernel−1 min−1 at 25 days after pollination and then declined throughout the remainder of kernel development. Embryo GS activity increased steadily throughout development to a maximum of 24 nmol γ‐glutamyl hydroxymate embryo−1 min−1 by 50 days after pollination. In contrast, endosperm GS activity, which was 25 nmol γ‐glutamyl hydroxymate endosperm−1 min−1 at 25 days after pollination, exhibited no discernable pattern of change during kernel development. These findings are discussed with respect to the possible roles PPCh, endosperm and embryo GS play in kernel development.
Response of aromatic‐pathway enzymes to changing physiological states of growth in suspension cultures of Nicotiana silvestris
Authors: Bonner Carol A. , Vrba Jacqueline , Jensen Roy A.
Published: May 2006

The activity levels of enzymes of aromatic amino acid biosynthesis respond to changing physiological states of growth, as illustrated by results obtained from suspension‐cultured cells of Nicotiana silvestris Speg. et Comes line ANS 1 (2N=24). The experimental system provides a foundation for interpretations about overall regulation of enzyme levels in relationship to growth physiology. Levels of activity for shikimate dehydrogenase (EC 1.1.1.25), prephenate aminotransferase and arogenate dehydrogenase were followed throughout a growth cycle obtained by a conventional subculture protocol. Enzyme date were also obtained from cell cultures maintained in continuous exponential growth for greater than 10 generations (EE cells). Both shikimate dehydrogenase and prephenate aminotransferase exhibited elevated stationary‐phase levels of enzyme, much of which was carried over into a subsequent subculture. At least 4 generations of exponential growth were required before diminution of the latter two enzymes to the levels characteristic of truly exponential‐phase growth (EE cells) occurred. This is reminiscent of the overall behavior of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate (DAHP) synthase (EC 4.1.2.15), specifically attributed to the properties of the cytosolic isozyme species (DAHP synthase‐Co). Elevation of arogenate dehydrogenase also occurred in stationary‐phase cells, but diminished rapidly during lag phase to reach the level characteristic of EE cells.
Proton pump activity in bundle sheath tissues of broad‐leaved trees in relation to leaf age
Authors: Wilson T. P. , Canny M. J. , McCully M. E.
Published: May 2006

The fluorescent probe sulphorhodamine G (SR) has been previously used as an indicator of low extra‐cellular pH and, by inference, of proton extrusion activity in living leaves. In legumes the SR uptake and proton extrusion was characteristic of the extended bundle sheath system (EBS) or paraveinal mesophyll, composed of bundle sheath cells and the related network of bridging cells between veins. This system has been identified as a site of temporary storage of amino carbon in soybean. A tree species. Populus deltoides Bartr. ex Marsh, was known both to have the EBS system in its leaves and to carry organic nitrogen in its xylem sap. It is now shown that P. deltoides also accumulates the SR probe in the EBS system. This association has been explored in 8 other broad‐leaved tree species. Seven of the 8 species have EBS systems and accumulate SR in them in early summer. The 8th species, Tilia americana L. has no EBS system and shows weak SR accumulation. The capacity to accumulate SR (and by inference to scavenge solutes from the transpiration stream) disappeared in all species at various stages in late summer. In two species, in addition, SR accumulation is interrupted for several weeks during fruit growth. It is proposed that EBS systems will be found in many dicotyledonous leaves, and will be found to scavenge solutes, especially organic nitrogen, from the xylem sap.
The influence of reduced photorespiration on long‐term growth and development of wheat
Authors: Gerbaud Alain , André Marcel , Gaudillère Jean‐Pierre , Daguenet Alain
Published: May 2006

The long‐term role of photorespiration was investigated by comparing growth, development, gas exchange characteristics and mineral nutrition of a wheat crop (Triticum aestivum L. cv. Courtot) cultivated in a culture chamber during a life cycle, either in 4% O2 or in normal O2 Low O2 pressure reduced photorespiration, but CO2 was controlled so that net photosynthesis remained the same as in the control crop. The growth and development of the low O2 crop was slowed down. Ear appearance was 16 days late, but the rate of tillering was the same as in the control and was maintained longer so that the final number of tillers was doubled. Pigment, ribulose bisphosphate carboxylase (EC 4.1.1.39) and soluble sugar contents were similar. The response of photosynthesis to CO2 and O2 was not appreciably changed by the low O2 treatment. There was almost no seed formation, and the senescence of the leaves was delayed. It appears that in non‐stress conditions most of the photorespiration can be suppressed without damage to the photosynthetic apparatus. Retardation of development and inhibition of reproduction are likely due to other effects of O2.
Seed dimorphism in Salicornia europaea: Nutrient reserves
Authors: Austenfeld Franz‐Arnold
Published: May 2006

Median and lateral seeds of Salicornia europaea L. were separately analysed for their sizes and nutrient reserves. The mean air‐dry weight of a single median and lateral seed was 0.31 and 0.25 mg, respectively. The composition as well as the concentration of the nutrient reserves were similar in both seed types. The bulk of the cations was derived from K+, followed by Mg2+, Na+ and Ca2+. The chloride content was somewhat higher than the sodium content, and phosphate was equalled by acid soluble Ca2+ and Mg2+. Starchy compounds and sucrose were present in equal amounts, each of them accounted for about 50% of the carbohydrates. Glucose and fructose were less than 1%. Protein‐nitrogen (ethanol‐insoluble N) was about 34 g (kg dry seeds)−1. About 7 g (kg dry seeds)−1 was ethanol‐soluble nitrogen, of which 10% was derived from amino acids. The total lipid content was more than 290 g (kg dry seeds)−1, 65% were calculated to be glycerides. More than 90% of the fatty acids consisted of linoleic and oleic acids, the majority (72%) of which was linoleic acid.
Early quantitative method for measuring germination in non‐green spores of Dryopteris paleacea using an epifluorescence‐microscope technique
Authors: Scheuerlein Robert , Wayne Randy , Roux Stanley J.
Published: May 2006

A method is described to determine germination by blue‐light excited red fluorescence in the positively photoblastic spores of Dryopteris paleacea Sw. This fluorescence is due to chlorophyll as evidenced from 1) a fluorescence‐emission spectrum in vivo, where a bright fluorescence around 675 nm is obtained only in red light (R)‐irradiated spores and 2) in vitro measurements with acetone extracts prepared from homogenized spores. Significant amounts of chlorophyll can be found only in R‐treated spores; this chlorophyll exhibits an emission band around 668 nm, when irradiated with 430 nm light at 21°C.

Compared to other criteria for germination, such as swelling of the cell, coat splitting, greening, and rhizoid formation, which require longer periods after induction for their expression, chlorophyll fluorescence can be used to quantify germination after two days. This result is confirmed by fluence‐response curves for R‐induced spore germination; the same relationship between applied R and germination is obtained by the evaluation with the epifluorescence method 2 days after the light treatment as compared with the evaluation with bright‐field microscopy 5 days after the inducing R.

Using this technique we show for the first time that Ca2+ contributes to the signaltransduction chain in phytochrome‐mediated chlorophyll synthesis in spores of Dryopteris paleacea.
Epi‐ and intracuticular lipids and cuticular transpiration rates of primary leaves of eight barley (Hordeum vulgare) cultivars
Authors: Svenningsson Magnus
Published: May 2006

The major constituents of the epi‐ and intracuticular lipids of primary leaves of 8 cultivars of barley (Hordeum vulgare L.) have been studied together with cuticular transpiration rates. The total amount of analysed cuticular lipids ranged from 9.6 to 13.4 μg cm−2 and was dominated by the epicuticular fraction, which made up 73–84% of the total. There were variations in the percentages of the analysed lipid classes, alkanes, esters, aldehydes, β‐diketones and alcohols, between epi‐ and intracuticular lipids among individual cultivars, but no clear tendency in these variations, except for the aldehydes, was found. The epicuticular lipids were richer in aldehydes than the intracuticular lipids. The cuticular transpiration rates were poorly correlated with the levels or composition of epi‐, intra‐ or total cuticular lipids. The cuticular transpiration rates were considerably altered as a response to a water stress treatment, but these changes could not be correlated with any changes in amount or composition of the cuticular lipids. From these results it is concluded that some property other than amount or composition of cuticular lipids is the most important in regulation of water diffusion through the cuticle.
Cadmium‐induced changes in the composition and structure of the light‐harvesting chlorophyll a/b protein complex II in radish cotyledons
Authors: Krupa Z.
Published: May 2006

Five‐day‐old etiolated radish (Raphanux salivuxL. cv. Saxa) seedlings exposed to white continuous light in the presence of Cd2+(0.2 mM) showed characteristic changes in their light‐harvesting chlorophylla/bprotein complex II after 48 h of greening. The content of its oligomeric supramolecular form was greatly diminished with a concomitant increase in the level of the monomer. The isolation of highly purified light‐harvesting chlorophylla/bprotein complex II from control and Cd2+treated radish cotyledons and a detailed analysis of its structure and composition revealed that first of all, Cd2+altered the content of the specific phosphatidylglycerol fatty acid ‐trans‐Δ3‐hexadecenoic acid, widely accepted as a component responsible for the oligomerization of this chlorophyll‐protein complex. This fatty acid in the thylakoid membrane phosphatidylglycerol pool seems to be very sensitive to different environmental stresses lowering its content, which indicates the vital significance of this component for the supramolecular organization and proper functioning of the light‐harvesting chlorophylla/bprotein complex II.
Effect of nitrate on nitrogen fixation and nodule carbohydrate and organic acid concentrations in pea mutants deficient in nitrate reductase
Authors: Nelson Louise M. , Edie Scott A.
Published: May 2006

Nitrate inhibits symbiotic N2 fixation and a number of hypotheses concerned with NO3− assimilation have been suggested to explain this inhibition. These hypotheses were tested using a pea (Pisum sativum L. cv. Juneau) with normal nitrate reductase NR; (EC 1,6,6,4) activity and two mutants of cv. Juneau, A317 and A334, with impaired NR activity. The plants were inoculated with three strains of Rhizobium leguminosarum and grown for 3 weeks in N‐free medium, followed by 1 week in medium supplemented with 0, 5 or 10 mM KNO3 before harvesting. NO3 was taken up at comparable rates by the parent and the mutants and accumulated in leaf and stem tissue of the latter. Acetylene reduction rates were inhibited similarly in both the parent and mutants in the presence of KNO3 but there were differences among rhizobial strains. Starch concentration of the nodules decreased by 46% in the presence of KNO3 and there were differences among rhizobial strains but not among pea genotypes. Malate and succinate accumulated in nodules in the presence of KNO3. These data are not consistent with the photosynthate deprivation hypothesis as a primary mechanism for NO3 inhibition of N2 fixation since NO3 affected the nodule carbohydrate composition of all three pea genotypes in a similar manner. The lack of correlation between NR activity and NO3 inhibition of N2 fixation suggests that NO3 assimilation may be only indirectly involved in the inhibition phenomenon.
Oxygen‐dependent stomatal opening in Zea mays leaves. Effect of Light and carbon dioxide
Authors: Vavasseur Alain , Lascève Gérard , Couchat Philippe
Published: May 2006

The oxygen requirement for stomatal opening in maize plants (Zea mays L. hybrid INRA 508) was studied at different CO2 concentrations and light intensities. In the absence of CO2, stomatal opening always required O2, but this requirement decreased with increasing light intensity. In darkness, the lowest O2 partial pressure needed to obtain a weak stomatal movement was about 50 Pa. This value was lowered to ca 10 Pa in light (320 μmol m−2 s−1).

On the other hand. in the absence of O2, CO2enabled stomatal opening to occur in the light, presumably due to the evolved photosynthetic O2. Thus, CO2, which generally reduced stomatal aperture, could induce stomatal movement in anoxia and light. The effect of CO2 on stomatal opening was closely dependent on O2 concentration and light intensity. Stomatal aperture appeared CO2‐independent at an O2 partial pressure which was dependent on light intensity and was about 25 Pa at 320 umol m−2 s−1.

The presence of a plasmalemma oxidase, in addition to mitochondrial oxidase, might explain the differences in the O2 requirement at various light intensities. The possible involvement of such a system in relation to the effect of CO2 is discussed.
Auxin‐induced N‐ethylmaleimide (NEM) effects on elongation growth of coleoptiles and auxin‐induced [14C]‐NEM labeling of membrane proteins
Authors: Spring Otmar , Wolz Christiane , Hager Achim
Published: May 2006

N‐ethylmaleimide (NEM) Lit 10‐100 μM led to a strong inhibition of the auxin‐induced elongation growth of colcoptile segments, while fusicoccin‐enhanced growth was not affected. Growth inhibition occurred only if NEM and auxin were allowed to act simultaneously. Preincubation of plant segments with NEM in the absence of auxin caused no inhibition of a subsequent growth stimulation by auxin, whenever NEM was removed before the application of IAA. However, preincubation with NEM plus auxin led to a remaining growth inhibition, which could not be reversed by a second auxin incubation in the absence of NEM. Fusicoccin added to NEM‐ plus auxin‐treated segments was able to restore growth. It is suggested that auxin causes the unmasking of essential SH‐groups of a protein to which NEM links covalently. thus inhibiting the growth process. This assumption was further supported by labeling experiments wish [14C]‐NEM using membranes of maize (Zea mays L. cv. Inraplus) coleoptiles. Two membrane fractions (S2= 480‐1900 g; S4= 4300‐15000 g) revealed a significantly higher [14C]‐NEM labeling in the presence of auxin (2,4‐diehlorophe‐noxyacctic acid compared to 2,6 dichlorophenoxyacetic acid). This effect disappeared when the membranes were previously washed with EGTA [ethyleneglycolbis‐(β‐aminoethylether)‐N,N,Nr′,N′‐tetraacetic acid]. The auxin‐induced sensitization of coleoptilc segments against thiol‐reagents and the auxin‐induced expression of SH‐groups of proteins of isolated membranes from coleoptiles arc suggested to be events involved in the primary action of auxins.
NADH‐dependent nitrate reductase from two‐row barley roots: Purification, characteristics and comparison with leaf enzyme
Authors: Oji Yoshikiyo , Takahashi Masakazu , Nagai Yasuo , Wakiuchi Nariaki
Published: May 2006

NADH‐nitrate reductase (EC 1.6.6.1) was purified 800‐fold from roots of two‐row barley (Hordeum vulgare L. cv. Daisen‐gold) by a combination of Blue Sepharose and zinc‐chelate affinity chromatographies followed by gel filtration on TSK‐gel (G3000SW). The specific activity of the purified enzyme was 6.2 μmol nitrite produced (mg protein)−1 min−1 at 30°C.

Besides the reduction of nitrate by NADH, the root enzyme, like leaf nitrate reductase, also catalyzed the partial activities NADH‐cytochrome c reductase, NADH‐ferricyanide reductase, reduced methyl viologen nitrate reductase and FMNH2‐nitrate reductase. Its molecular weight was estimated to be about 200 kDa, which is somewhat smaller than that for the leaf enzyme. A comparison of root and leaf nitrate reductases shows physiologically similar or identical properties with respect to pH optimum, requirements of electron donor, acceptor, and FAD, apparent Km for nitrate, NADH and FAD, pH tolerance, thermal stability and response to inorganic orthophosphate. Phosphate activated root nitrate reductase at high concentration of nitrate, but was inhibitory at low concentrations, resulting in increases in apparent Km for nitrate as well as Vmax whereas it did not alter the Km for NADH.