bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of proteins during the development of the first leaf of oat (Avena sativa)
Authors: Klerk H. , Tophof S. , Van Loon L. C.
Published: May 2006

Distal segments of the first leaf of intact oat (Avena sativa L. cv. Victory) plants at different stages of development were labelled with 35S‐methionine. During 12‐h labelling periods similar amounts of label were retained in the segments, but incorporation into protein decreased from 28% in 7‐day‐ to 3% in 27‐day‐old plants. Two‐dimensional polyacrlamide gel electrophoretic analysis of the proteins revealed that even at a late stage of senescence a great many proteins are still being synthesized. Synthesis of ribulosebisphosphate carboxylase and other chloroplast‐associated proteins declined more rapidly than general protein synthesis. With increasing leaf age, two sets of proteins with a relatively high molecular weight around 67 kDa and isoelectric points between 6.5 and 6.8 became the most prominently synthesized proteins. Since these proteins were hardly visible upon silver‐staining, they seem to be subject to rapid turnover. An involvement of these proteins in senescence might explain the requirement of protein synthesis for senescence to proceed.
Flowering strategies of the high‐arctic and high‐alpine snow bed grass species Phippsia algida
Authors: Heide O. M.
Published: May 2006

Flowering requirements of the high‐arctic and high‐alpine snow bed grass species Phippsia algida (Sol.) R. Br. have been studied in controlled environments. Seedlings flowered rapidly in continuous long days (LD) at temperatures ranging from 9 to 21°C. They also initiated inflorescence primordia at the same temperatures in continuous short days (SD), whereas LD were required for heading and anthesis. The plant thus has the characteristics of a regular long day plant, although the daylength requirement is associated with floral development only. The critical daylength for the LD response was about 17 h at 21°C and 19 h at 9°C. A single LD cycle was enough to trigger inflorescence development, while 5 cycles were required for the full response. Anthesis was reached within a week of LD treatment at 21°C in SD grown plants with preformed inflorescence primordia. The advantages of these versatile flowering responses are discussed in relation to the extreme climatic regime of late snow bed sites.
Influence of air pollutants and nutrient deficiency on D‐1 protein content and photosynthesis in young spruce trees
Authors: Lütz C. , Steiger A. , Godde D.
Published: May 2006

Long‐term fumigation with different mixtures of air pollutants, such as O3, NO2 and SO2, in combination with potassium deficiency in 4‐year‐old spruce trees shows clearly that the photosynthetic apparatus reacts very sensitively to environmental stress. Even when no change in photosynthetic oxygen evolution of the leaves was measurable, the content of D‐1 protein in the reaction center of photosystem II already increased significantly at low stress conditions. With increasing concentrations of pollutants, the content of D‐1 protein decreased considerably. This pattern was observed with all combinations of gases, although they differed in effectiveness. The most potent effect on the content of D‐1 protein was found with a combined fumigation of SO2 plus NO2. Obviously, the ratio between synthesis and degradation of the D‐1 protein is influenced by stress factors. However, the content of D‐1 protein was not strongly correlated with photosynthetic oxygen evolution in whole needles nor with electron transport rate in isolated thylakoids. Under controlled potassium deficiency, effects similar to those observed upon ozone fumigation developed. The results suggest unspecific stress answers for the D‐1 content and the photosynthetic reactions rather than specific responses.
The fate of apoplastic sucrose in sink and source leaves of Urtica dioica
Authors: Möller Ina , Beck Erwin
Published: May 2006

Experiments were performed with developing and mature leaves of Urtica dioica L. to trace differences which could be interpreted in terms of cell wall‐bound acid invertase (EC 3.2.1.26) participating in phloem unloading in a sink leaf. The pH of apoplastic fluid that was collected by gentle centrifugation of entire leaves was identical (7.1) in the two types of leaves; also, fluorometric determination with esculetin showed a neutral apoplastic pH between 7.0 in the source and 7.2 in the sink leaf. To detect whether differences in apoplastic pH occur within limited leaf areas, such as of the tissue surrounding the veins, the metabolic fate of [14C]–(fructosyl)‐sucrose that was administered via the xylem was investigated. In source leaves, there was a large transitory decrease in [14C]‐sucrose followed by a substantial resynthesis of this compound. In sink leaves, resynthesis was less significant and carbon was incorporated mainly in starch, charged soluble compounds and cell walls. However, after correction for resynthesis, the two types of leaves showed an identical capacity for sucrose cleavage. Finally, activation of the apoplastic invertase by administering labelled sucrose in buffered solution of pH 5.0 did not result in an enhanced degradation. By contrast, apoplastic fluid collected from leaves which had been infiltrated with buffer solutions of pH 5.5 and 8.0, respectively, showed a rapid adjustment of the pH close to the natural neutral value by the mesophyll tissue. The results are incompatible with the idea of an active invertase in the sink (and the source) leaves apoplast, and hence do not lend support to the theory of apoplastic cleavage of sucrose being required for phloem unloading in this kind of a utilization sink.
Comparison of three DNA fluorochromes for flow cytometric estimation of nuclear DNA content in plants
Authors: Doležel Jaroslav , Sgorbati Sergio , Lucretti Sergio
Published: May 2006

Flow cytometric estimation of nuclear DNA content was performed in six plant species employing three fluorochromes showing different DNA base preferences: propidium iodide (no base preference), 4′,6‐diamidino‐2‐phenylindole (DAPI; AT preference), and mithramycin (GC preference). Nuclei isolated from human leukocytes were used as a primary reference standard. While nuclear DNA contents estimated using propidium iodide were in agreement with published data obtained using other techniques, the values obtained using fluorochromes showing base preference were significantly different. It was found that the differences were caused by the differences in overall AT/GC ratios, and by the species‐specific differences in binding of these fluorochromes to DNA. It was concluded that nuclear DNA content estimations performed with fluorochromes showing base preference should be interpreted with caution even when AT/GC ratios of the reference and the sample are equal. The use of intercalting dyes (e.g. propidium iodide) is recommended for this purpose. On the other hand, comparison of the staining behaviour of intercalating dyes with that of dyes showing base preference may give additional information on chromatin structural differences and arrangement of molecule pairs in DNA.
Blue, red and blue plus red light control of chlorophyll content and CO2 gas exchange in barley leaves: Quantitative description of the effects of light quality and fluence rate
Authors: Bukhov N. G. , Drozdova I. S. , Bondar V. V. , Mokronosov A. T.
Published: May 2006

The dependence of the Chl content and the rate of CO2 gas exchange (RGE) on both blue and red quanta fluence rates have been studied in primary leaves of barley (Hordeum vulgare L. cv. Viner). Empirical equations connecting the two photosynthetic indices with fluence rates of blue or red light were developed. These equations consist of 3 (Chl content) or 2 (RGE) terms, each reflecting the involvement of a specific reaction in the long‐term light control of the development of the photosynthetic apparatus. On the basis of the equations the effects of mixed blue plus red light on both the Chl content and RGE were calculated. An additive mode of the co‐action of blue and red light in the range of high PFDs (10–170 μmol m−2 s−1) becomes evident from the comparison of the experimental results and calculated data. The results indicate the involvement of phytochrome, cryptochrome and chlorophyll in the long‐term regulation of the Chl content and RGE.
Drought tolerance in faster‐ and slower‐growing black spruce (Picea mariana) progenies: I. Stomatal and gas exchange responses to osmotic stress
Authors: Tan Weixing , Blake Terence J. , Boyle Timothy J. B.
Published: May 2006

Sixteen years growth in height and basal stem diameter of full‐sib black spruce [Picea mariana (Mill.) B. S. P.] progenies varied with soil moisture availability. The responses to water stress of two faster‐growing progenies under drought were compared with two slower‐growing progenies to determine the physiological basis of drought tolerance. Six‐month‐old seedlings were stressed using an osmoticum, polyethylene glycol‐3350 (PEG). Seedlings were passed through a series of increasing concentration: 10, 18 and 25% PEG (w/v) each for 3 days to provide solution water potentials of ‐0.4, ‐1.0, and ‐2.0 MPa, respectively. The stress was then relieved by returning the seedlings to nutrient solution without PEG for 24 hours. Gas exchange and water relation parameters were similar in the 4 progenies prior to the imposition of the stress but varied during the stress and after stress relief. The two progenies which grew more vigorously on the driest site maintained significantly higher stomatal conductance, leaf transpiration rate, and net photosynthesis rate during mild (10% PEG) and moderate (18% PEG), but not severe (25% PEG) osmotic stress, and also recovered faster after release of the stress than the other two slower‐growing progenies. Black spruce progenies did not differ in xylem water potential or water use efficiency. Progenies capable of faster growth under drought stress were thus characterized by a greater dehydration tolerance, rather than postponement, compared with slower‐growing progenies.
Drought tolerance in faster‐ and slower‐growing black spruce (Picea mariana) progenies: II. Osmotic adjustment and changes of soluble carbohydrates and amino acids under osmotic stress
Authors: Tan Weixing , Blake Terence J. , Boyle Timothy J. B.
Published: May 2006

The possibility was considered that osmotic adjustment, the ability to accumulate solutes in response to water stress, may contribute to growth rate differences among closely‐related genotypes of trees. Progeny variation in osmotic adjustment and turgor regulation was investigated by comparing changes in osmotic and pressure potentials, soluble carbohydrates, and amino acids in osmotically stressed seedlings in 4 full‐sib progenies of black spruce [Picea mariana (Mill.) B. S. P.] that differed in growth rate under drought. Osmotic stress was induced by a stepwise increase in the concentration of polyethylene glycol (PEG)‐3350 from 10 (w/v) to 18 and 25%, which provided osmotic potentials in solution culture of ‐0.4, ‐1.0 and ‐2.0 MPa each for 3 days. All 4 progenies maintained a positive cell turgor even at 25% PEG, due to a significant decline in osmotic potential. Although total amino acids, principally proline, increased, ca 60% of the decrease in osmotic potential was attributable to soluble carbohydrates and glucose was the major osmoregulating solute. There was little progeny variation in any of measured parameters in unstressed seedlings. Compared to two slower‐growing progenies, the two progenies capable of more vigorous growth under drought in the field accumulated more soluble carbohydrates (mainly glucose and fructose), developed lower osmotic potential and maintained higher turgor pressure when osmotically‐stressed in solution culture. The ability to adjust osmotically and maintain turgor under drought stress could thus be a useful criterion for the early selection of faster‐growing, drought‐tolerant genotypes.
Growth, photosynthesis, respiration, and intracellular free amino acid profiles in the unicellular alga Cyanidium caldarium. Effect of nutrient limitation and resupply
Authors: Vona Vincenza , Di Martino Rigano Vittoria , Esposito Sergio , Di Martino Catello , Rigano Carmelo
Published: May 2006

Growth, intrácellular free amino acid pools and photosynthetic and respiratory activities in nutrient sufficient cells and in N‐ K‐ and P‐limited cells of Cyanidium caldarium (Tilden) Geitler, and responses to nutrient resupply were investigated. Addition of ammonium to N‐limited cells and of phosphate to P‐limited cells resulted in a stimulation of dark respiration and in a decrease in photosynthetic oxygen evolution. Addition of K to K‐limited cells had no effect on rates of photosynthesis and respiration. Nutrient limited cells and sufficient cells exhibited different free amino acid profiles. Upon resupply of ammonium to N‐limited cells levels of glutamine, citrulline, arginine, alanine, and serine increased. Also the levels of δ‐aminolevulinic acid (δ‐ALA) and putrescine increased notably. On adding phosphate to P‐limited cells the level of glutamate decreased significantly whereas the level of alanine increased and the concentrations of other amino acids remained unaffected. On adding potassium to K‐limited cells there was an increase in glutamate and citrulline concentrations, and a decrease in putrescine concentration, whereas concentrations of arginine and alanine remained at the very high levels observed already before addition. Resuspension of N‐ and K‐limited cells in a complete growth only after 25‐30h. In P‐limited cells resumption of growth in complete medium occurred progressively and reached the maximum rate 30h later. P‐, K‐ and N‐ limited cells resuspended into sufficient media showed different rates of ammonium and phosphate assimilation. The pattern of recovery from nutrient limitation is discussed according to the cellular role fulfilled by the nutrient which was growth rate‐limiting.
Isoelectric focusing of pigment‐protein complexes solubilized from non‐irradiated and irradiated prolamellar bodies
Authors: Wiktorsson Bengt , Ryberg Margareta , Gough Simon , Sundqvist Christer
Published: May 2006

Preparative isoelectric focusing was employed to compare the association of protochlorophyllide and chlorophyllide with the enzyme NADPH‐protochlorophyllide oxidoreductase (PCR; EC 1.3.1.33). Photoactive protochlorophyllide‐PCR complexes were solubilized with 1‐O‐n‐octyl‐β‐d‐glucopyranoside from non‐irradiated prolamellar bodies of wheat (Triticum aestivum). Also, chlorophyllide‐PCR complexes were solubilized from prolamellar bodies irradiated under conditions either preventing or favouring a spectral shift of chlorophyllide to shorter wavelengths. Independently of the treatment prior to the solubilization, the pigments and the PCR focused together at pHs of 4 to 5. The results indicate that protochlorophyllide‐PCR complexes are conformationally similar to chlorophyllide‐PCR complexes. The results support the hypothesis that the spectral shift, referred to as the Shibata shift, reflects a breaking‐up of large chlorophyllide‐PCR aggregates to smaller chlorophyllide‐PCR units, rather than a dissociation of the chlorophyllide from the enzyme protein.
Abscisic acid effects on intracellular pH and ion fluxes in barley leaf segments
Authors: Beffagna Nicoletta
Published: May 2006

Changes in intracellular pH and in H+, K+ and Cl− fluxes were evaluated in different experimental conditions in leaf segments of barley (Hordeum vulgare cv. Georgie) incubated in the dark, at pH 5.5, in the presence or absence of abscisic acid (ABA), and a comparison was made between the effects of ABA and those of erythrosin B (EB), a plasmalemma H+‐pump inhibitor. In all conditions tested, ABA induced a cell sap acidification, an alkalinization of the external medium, a decrease in K+ intracellular contents, and an increase in the contents of Cl−. The ABA‐induced decrease in K+ content was chiefly due to the inhibition of K+ influx. On the contrary, ABA did not influence the uptake of Cl−, but inhibited Cl− efflux, the inhibition satisfactorily accounting for the larger Cl− content observed in the presence of the hormone. The intracellular acidification and the decrease in apparent outward net transport of H+ observed with ABA were seemingly not associated with the activity of the proton pump, the transmembrane electrical potential difference, or K+ transport. On the contrary, a correlation was evident with the changes in Cl− content. These results and, in particular, the similarity between the effects of ABA and those induced by 4,4 ‐diisothiocyano‐2,2‐disulfonic acid stilbene (DIDS), a Cl− channel‐blocking agent, suggest that the ABA‐induced changes in intracellular pH and in H+ transport might depend on the capability of ABA to inhibit Cl− efflux, more than on a primary inhibition of the H+ pump, and propose an important role for ABA in regulating the Cl− channels.
Correlation between the expression of T‐DNA IAA biosynthetic genes from developmentally regulated promoters and the distribution of IAA in different organs of transgenic tobacco
Authors: Sitbon Folke , Anthony Little C. H. , Olsson Olof , Sandberg Göran
Published: May 2006

To alter the level and distribution of IAA in tobacco, the T‐DNA iaaM gene was fused to the TR‐DNA 1′ promoter, and this construct was used to transform transgenic tobacco SR1 plants containing the natural iaaH gene. Coexpression of the 1’‐iaaM and iaaH genes was associated with reduced plant height, leaf size, and internode diameter. Free and conjugated IAA levels were higher in 1′‐iaaMliaaH plants than in wild‐type, most notably in the basal leaves and internodes. Extending this work, hygromycin‐resistant plants containing the iaaM gene expressed from either the 1′, CaMV 35S or potato ST‐LS1 promoters were crossed with a kanamycin‐resistant 35S‐iaaH plant. Transcription of the iaaM and iaaH genes, and levels of IAA and ABA were monitored in hygromycin‐ and kanamycin‐resistant progeny. Growth was inhibited in all lines, particularly in 35S‐iaaM x 35S‐iaaH plants. The phenotypes of 1′‐iaaM x 35S‐iaaH and 35S‐iaaM x 35S‐iaaH plants were similar to those of 1′‐iaaMliaaH and 35S‐iaaMliaaH plants, respectively, indicating that iaaH expression does not limit IAA biosynthesis. Transcription of the iaaM gene varied between the lines, as well as within and between organs of the same line. An increased IAA level was associated with iaaM transcription in most organs. Overall, the ABA level was higher in wild‐type than in transgenic lines, but did not vary between the transgenic lines.
Differential expression of CuZn‐superoxide dismutases in Pinus sylvestris needles exposed to SO2 and NO2
Authors: Karpinski Stanislaw , Wingsle Gunnar , Karpinska Barbara , Hällgren Jan‐Erik
Published: May 2006

Mature Pinus sylvestris trees were exposed to air‐pollution strees in an open field fumigation experiment. The trees were exposed to low‐levels of sulphur dioxide and nitrogen oxides throughout the whole growing season (June to October 1991). Three age‐classes (current, one‐ and two‐year‐old) of needles were collected from exposed and control trees and the expression of chloroplastic and cytosolic CuZn‐superoxide dismutase (SOD; EC 1.15.1.1) genes was studied. The levels of chloroplastic and cytosolic CuZn‐SOD mRNA were significantly (up to 2.3‐fold) higher in exposed trees for all age‐classes of needles as compared to control trees. No significant differences were observed between different needle age‐classes in CuZn‐SOD mRNA induction. The chloroplastic and cytosolic CuZn‐SOD mRNA were induced to the same extent, however, the level of chloroplastic CuZn‐SOD mRNA was higher than the cytosolic one. Small differences were observed in CuZn‐SOD mRNA levels for individual trees both within exposed and control areas. Protein activity measurements of the CuZn‐SOD isozymes did not reveal any significant differences between control and exposed trees. The results are discussed in relation to protection against oxidant stress from air pollutants.
Growth kinetics, polyamine pattern and biosynthesis in hairy root lines of Nicotiana tabacum
Authors: Mengoli Marisa , Ghelli Anna , Chriqui Dominique , Bagni Nello
Published: May 2006

The possibility of a relation between the expression of root inducing (Ri) T‐DNA genes of Agrobacterium rhizogenes and changes in polyamine metabolism has been explored in fast‐growing tobacco hairy roots. Transformed root cultures have been established on hormone‐fee medium; they came from transgenic plants of Nicotiana tabacum L. cv. Xanthi with different altered phenotypes, designated transformed (T) and supertransformed (T'). T and especially T′ roots developed more rapidly both by elongation and lateral branching, and showed a higher growth rate than the untransformed control. After 3 weeks in culture, normal roots showed a very reduced meristematic zone, and flow cytometric analysis indicated that 2C nuclei were predominant in the apical parts in contrast to T and T′ roots, in which endopolyploidisation also appeared. Putrescine, spermidine and traces of spermine were present in all the samples, both in free and in conjugated forms. Putrescine was the major polyamine detected in controls and in transformed roots. At the time of excision, the polyamine levels were similar in normal, T and T′ roots. Significant differences were found during the progression of growth, particularly in the TCA‐insoluble fraction in which polyamines varied differently according to the type of roots, increasing considerably in T roots on day 8, then decreasing. The lower polyamine contents found in growing transformed roots were concomitant to low arginine (EC 4.1.1.19) and ornithine (EC 4.1.1.17) decarboxylase activities. It is suggested that polyamine levels and related enzyme activities are linked to growth kinetics rather than being a consequence of foreign gene expression.
Pathogenesis‐related protein b1′′ in plants and in cell suspension cultures of Nicotiana glutinosa Nicotiana debneyi and an amphidiploid cross (N. glutinosa×N. debneyi)
Authors: Gügler Karl , Défago Geneviève , Brodelius Peter E.
Published: May 2006

The expression of PR‐protein b1′′ in plants and cell suspension cultures of Nicotiana glutinosa L., Nicotiana debneyi Domin, and an amphidiploid cross of these two species, a hybrid, has been investigated. An enzyme linked immunosorbent assay has been employed to determine the concentration of PR‐protein b1′′ in extracts. The PR‐Protein b1′′ was constitutively produced in intact plants of the hybrid (around 25 μg g−1 leaf tissue), while only trace amounts of the protein (< 50 ng g−1 leaf tissue) were found in plants of the two parents. In suspension culture, the concentrations of PR‐protein b1′′ were 8, 0.4 and less than 0.1 mg l−1 medium for the hybrid. N. debneyi and N. glutinosa, respectively. Only trace amounts of the protein were found in extracts from cells. Seven days after infection by tobacco mosaic virus (TMV) the concentration of PR‐protein b1′′ in leaves of N. glutinosa was 22.5 μg g−1 leaf tissue. In N. debneyi and the hybrid a relatively limited induction of PR‐protein b1′′ by TMV was observed. The influence of various phenoxyacetic acids on the expression of PR‐protein b1′′ in the 3 cell cultures has been investigated. Cultures of N. glutinosa responded to treatments with 2,4‐D and 2,4,5‐T while cultures of N. debneyi and the hybrid were essentially unaffected. In the former case a concentration of 5–10 mg l−1 2,4,5‐T was optimal and cells were most responsive to the treatment 4 days after subcultivation. The concentration of PR‐protein b1′′ in elicited cell cultures of N. glutinosa was 2 to 4 mg l−1 medium.
Effects of dicyclohexylcarbodiimide (DCCD) treatment on coupled activities of vanadate‐sensitive ATPase from plasma membrane of maize roots
Authors: Hsu An‐Fei , Rodenbach Stacey , Tu Shu‐I
Published: May 2006

The presence of dicyclohexylcarbodiimide (DCCD) inhibited the activities of vanadate‐sensitive H+ ‐ATPase in both native and reconstituted plasma membrane of maize (Zea mays L. cv. WF9 × Mo 17) roots. Concentration dependence of DCCD inhibition on adenosine triphosphate (ATP) hydrolysis of native plasma membrane vesicles suggested that the molar ratio of effective DCCD binding to ATPase was close to 1. The DCCD inhibition of ATP hydrolysis could be slightly reduced by the addition of ATP, Mg:ATP, adenosine monophosphate (AMP), Mg:AMP and adenosine diphosphate (ADP). More hydrophilic derivatives of DCCD such as l‐ethyl‐N?‐3‐trimethyl ammonium carbodiimide (EDAC) or 1‐ethyl‐3‐3‐dimethyl‐aminopropyl carbodiimide (EDC) gave no inhibition, indicating that the effective DCCD binding site was located in a hydrophobic region of the protein. The proton transport activity of reconstituted plasma membrane at a temperature below 20°C or above 25°C was much sensitive to DCCD treatment. Build‐up of the proton gradient was analyzed according to a kinetic model, which showed that proton leakage across de‐energized reconstituted plasma membranes was not affected by DCCD, but was sensitive to the method employed to quench ATP hydrolysis. Reconstituted plasma membrane vesicles treated with DCCD exhibited a differential inhibition of the coupled H+‐transport and ATP hydrolysis. The presence of 50 μM DCCD nearly abolished transport but inhibited less than 50% of ATP hydrolysis. The above results suggest that the link between proton transport and vanadate‐sensitive ATP hydrolysis is indirect in nature.
Cytokinins in a genic male sterile line of Brassica napus
Authors: Shukla Amit , Sawhney V. K.
Published: May 2006

Endogenous cytokinin levels were analyzed in four different organs viz., root, stem, leaf and mature flower, of the wild type (cv. Westar) and a genic male sterile (GMS) line of Brassica napus. Various cytokinins viz., bases (Z, DZ), ribosides (ZR, DZR), glucosides (OGZ + OGZR, OGDZ + OGDZR) and nucleotides (ZNT, DZNT) were quantified using Amaranthus betacyanin bioassay and ELISA. The major cytokinin in all the organs was DZ. In general, leaves had the highest levels of cytokinins as compared to the other organs. Root, stem and mature flowers of the wild type plants had higher levels of cytokinins and their metabolites than the GMS line. However. levaves of the GMS line had greater amount of various cytokinins as compared to the wild type. The major cytokinin quantitatively different between the two lines was DZ. The results suggest the possible involvement of cytokinins in the expression of genic male sterility in Brassica napus.
Induction of nitrate reductase in detached corn leaves: the effect of the age of the leaves
Authors: Kenis J. D. , Silvente S. T. , Luna C. M. , Campbell W. H.
Published: May 2006

It is generally accepted that young leaves have higher nitrate reductase (NR) activity than older ones. To determine the physiological basis of this observation and gain a better understanding of the regulation of NR activity, we investigated NR activity and protein and NR mRNA in corn (Zea mays L.) leaves of different age induced with ammonium nitrate. Using detached leaves to facilitate control over nitrate availability and evaluation of protein synthesis, we found that when exposed to ammonium nitrate, the younger (3‐day‐old) leaves developed higher levels of NR activity and protein (assayed with an enzyme‐linked immunosorbent assay) than the older (5‐day‐old) leaves. This difference in response appeared not to be due to a higher decay rate of enzyme activity in older leaves. Evaluation of soluble protein synthesis using labelled methionine indicated that the rates of synthesis were significantly higher in the younger than in the older tissue, but rates of protein turnover (assayed with an unlabelled methionine chase) were also higher. NR protein was also synthesized and degraded more rapidly in younger leaves. The higher steady‐state level of nitrate reductase activity and protein in 3‐day‐old leaves apparently resulted from a greater net synthesis of enzyme protein, which reflected the higher total rate of synthesis of soluble protein in younger leaves. RNA blots of NR mRNA showed that the transcript levels were similar in 3‐ and 5‐day‐old leaves. This indicates that the NR gene was equally responsive to ammonium nitrate induction in the two ages of leaves. Our results show a poor correlation between the level of NR transcript and the amount of NR protein synthesized from it in leaves of different age. The data suggest that the NR transcript is used much less efficiently for production of NR protein in the older than in the younger leaves. We conclude that this low efficiency can account for the decrease in NR activity and protein found in older leaves.
A rhythm in the flowering response of photoperiodically‐induced Pharbitis nil to agents affecting cytosolic calcium and pH
Authors: Friedman Haya , Goldschmidt Eliezer E. , Spiegelstein Hanna , Halevy Abraham H.
Published: May 2006

Previous work with modulators of Ca2+ and pH has indicated that elevated levels of cytoplasmic Ca2+ and pH are required during the first 4‐5 h of the dark period for successful floral induction in Pharbitis nil Chois cv. Violet. In the present study we further examined the effect of modulators of Ca2+ and pH by supplying them at various times prior to the inductive dark period. Peaks of inhibition by the Ca2+ chelator, EGTA, were observed in seedings treated 8, 18‐and 34 h before the start of the dark period. When seedlings of slightly different ages (within one diurnal cycle) were treated with EGTA, maximum inhibition was always obtained in plants treated 8 h before the start of the dark period. Peaks of inhibition by the acidifying agents, salicylic acid and Na‐propionate, were observed at ‐2 to ‐6 h and at ‐10 to ‐ 14 h. Treatment with the alkalizing agent, trisodium citrate, enhanced the flowering response with maximum enhancement at ‐6 to ‐8 h and at ‐ 18 to ‐ 20 h. We hypothesize that treatment with modulators starts an oscillation in endogenous levels of Ca2+ and pH. The levels of Ca2+ and pH prevailing at the commencement of the inductive dark period will influence the ability of the plant to perceive or to respond to the photoperiodic induction.
Gene expression during two alternative pathways of ovary development in Pisum sativum: fruit development and ovary senescence
Authors: Sánchez‐Beltrán María‐José , Carbonell Juan , García‐Martínez José L. , López‐Díaz Isabel
Published: May 2006

Pea ovaries are induced to enter a fruit development pathway involving physiological and morphological changes by pollination or application of plant growth regulators. In the absence of these stimuli, overies stop growing and enter an alternative pathway of senesecence that leads to their degeneration. We have used two dimensional polyacrylamide gel electrophoresis in search of molecular changes underlying fruit development and ovary senescence at the level of total accumulated proteins, newly synthesized proteins, and translatable, RNA populations. We have found changes in gene expression during the processes of ovary formation and ovary senescence. Stimuli that induce fruit set do not appreciably alter the overall patterns of synthesized proteins or translatable RNAs, indicating that fruit development is apparently a natural continuation of ovary formation. However, ovary senescence is an alternative pathway that involves the presence of new RNA messengers and proteins as well as the disappearance of others. These changes were detected earlier than any morphological or structural changes could be observed in the ovary.
Effect of drought stress on proteolytic activities in Phaseolus and Vigna leaves from sensitive and resistant plants
Authors: Roy‐Macauley H. , Zuily‐Fodil Y. , Kidric M. , Thi A. T. Pham , de Silva J. Vieira
Published: May 2006

Although much information is available concerning the effect of senescence on cell proteolytic activities, few reports are devoted to the impact of drought stress. Our aim was to study the influence of water deficit on the cell proteolytic potential, and to determine whether or not it could be used as a physiological parameter for screening varieties for tolerance to drought. We have used Phaseolus and Vigna species differing in their senstivity to water deficit: V. unguiculata L. Walp. cv. EPACE (resistant), V. unguiculata L. Walp. cv. IT83D (moderately senstive) and P. vulgaris L. cv. Carioquinha (sensitive). The plants were subjected to controlled water conditions. Proteolytic activities were assayed using azocasein in the case of leaf extracts and [14C]‐methylated casein in the case of cell compartments: soluble fraction, membrane fraction and isolated, purified chloroplasts. The results indicate that the leaf extracts contained 3 groups of proteinases with optimum pH at 4.5, 5‐6 and 8.5 for the Vigna cultivars and 5.0, 6.5 and 9.0 for the Phaseolus cultivar. The sensitive P. vulgaris Carioquinha showed higher caseinolytic activities than the other tow cultivars in response to water deficit. As regards cell fractions, proteolytic activities were determined for pH values of 4.5, 6.0 and 9.0. In soluble fractions of stressed plants, proteolytic activities increased at all the pH values tested; this clearly correlated with the drought sensitivity level of the plants, especially at pH 4.5. The same phenomenon was observed in the case of membranes and purified chloroplasts of the sensitive cultivar. Under drought stress, the proteolytic potential of the cell increased especially in the vaculoar sap (soluble fraction). The higher activities observed for all the cell compartments in the sensitive cultivar could be responsible, at least partly, for the rapid degradation of leaf and chloroplast proteins under drought. The use of [14C]‐methylated casein and soluble cell fractions seem to allow a clear differentiation between cultivars with respect to the drought tolerance at the cellular level.
Changes with time in the H+ concentration of the culture medium influences morphogenesis in tobacco thin cell layers
Authors: Cousson Alain , Tran Thanh Van Kiem , Trinh Toan Hanh
Published: May 2006

Different types of morphogenesis in thin cell layers of Nicotiana tabacum cv. Samsun were studied in relation to changes in the external H+ concentration during cluture. Different initial pHs of the medium, ranging from 3.83 to 6.35, were tested under unbuffered and MES‐buffered conditions, in combination with various amounts of indolyl‐3‐butyric acid and kinetin. The explants were sequentially transferred from MES‐free media to MES‐supplemented media, as well as reciprocally, to determine possible periods during the morphogenic process that showed a particular sensitivity to the external pH. Starting from pH 3.83, 36 mM MES induced the formation of limited callus and of vegetative and floral shoots as flowers in the control. MES at 50 mM inhibited rhizogenesis and either prevented morphogenesis or induced vegetative buds or flowers, depending on the initial pH. The 4th day of culture was a determining period in the induction of roots and flowers. Rhizogenesis, but not floral or vegetative organogenesis, was related to the theoretical intracellular concentration of indolyl‐3‐butyric acid. H+ transport might be involved in the regulation of morphogenesis.
Light‐induced changes of photosystem II activity in dark‐grown Scots pine seedlings
Authors: Jansson Stefan , Virgin Ivar , Gustafsson Petter , Andersson Bertil , Öqulst Gunnar
Published: May 2006

Both chlorophyll a and b and polypeptides of the photosynthetic apparatus are found in gymnosperm seedlings. germinated and grown in absolute darkness. The photosystem II (PSII) activity is, however, limited, probably due to an inactive oxygen evolving system. In the present study dark‐grown seedlings of Scots pine (Pinus sylvestris L.) were transferred to light and changes in antenna size and the activation process of PSII were investigated using fluorescence measurements and quantitative western blotting. It was found that the activation process is rapid, requires very little light and that strong light inhibits the process. It takes place without any changes in the primary reactions of PSII. Furthermore, all polypeptides except the major light‐harvesting chlorophyll a/b‐binding protein complex of PSII (LHCII) were present in dark‐grown seedlings in amounts comparable to the light treated control. The dark‐grown seedlings had the same LHCII polypeptide composition as light treated seedlings, and the LHCII present seemed to be fully connected to the reaction centre. The results indicate that activation of PSII in dark‐grown conifer seedlings resembles the photoactivation process of angiosperms. This implies that the fundamental processes in the assembly of the photosystem II complex is the same in all plants, but that the regulation differs between different taxa.
Subcellular compartmentation of pyrophosphate and dark/light kinetics in comparison to fructose 2,6‐bisphosphate
Authors: Eberl Dagmar , Preissler Manuela , Steingraber Manfred , Hampp Rüdiger
Published: May 2006

Subcellular compartmentation of pyrophosphate (PP1) was determined by rapid membrane filtration of evaeuolated oat mesophyll protoplasts. By improving both the extraction procedure and its assay via bioluminescence, PP1 recovery from samples was quantitative and linear down to below 200 fmol. Based on the content of the different fractions obtained after membrane filtration and compared to the respective pools of marker metabolites [cytosol, fructose 2,6‐bisphosphate (F26BP); chloroplast stroma, ribulose bisphosphate] rather than enzymes, we found ca 2/3 of the total cellular content to be chloroplast‐assotiated. Referred to compartmental volumes, cytosolic and stromal concentrations of PP1 were nearly equal (70–100 μM). PP1 was higher in evacuolated compared to racuotated protoplasts which indicates a possible role of the tonoplast‐located H+ pumping PP1ase in regulating the cellular pool size of PP1. During dark‐light‐transition the pool sizes of PP1 changed only marginally in both vacuolated and evacuolated protoplasts, while there were pronounced changes in those of F26BP, starch and sucrose. Thus our findings support the notion that the cellular pool size of PP1 is kept rather constant. They are, however, in contrast to the assumption that appreciable PP1 levels only exist in the cytosol.
Germination and ion leakage are linked with phase transitions: of membrane lipids during imbibition of Typha latifolia pollen
Authors: Hoekstra Folkert A. , Crowe John H. , Crowe Lois M.
Published: May 2006

In previous studies on the causes of imbibitional leakage in dry polien we have presented data which suggest that the leakage is due to a gel to liquid crystalline phase transition in membrane phospholipids during the rehydration event. In the present study we greatly extend and confirm those results. A supplemented phase diagram for the hydration dependent transition temperature of membrane phospholipids in pollen is presented. In pollen containing > 0.05 g H2O g−1 dry weight at the time of imbibition, this phase diagram for the phospholipids precisely predicts the conditions for rehydration under which germination is maximal and leakage is minimal. However, in extremely dry pollen, containing < 0.05 g H2O g−1 dry weight the predictive value of the phase diagram for phospholipids in the pollen is not in agreement with data for germination and leakage. Thus, an alternative explanation must be sought for leakage in these circumstances. We examined the available evidence and suggest here that a modified form of the non‐bilayer phase hypothesis proposed by Simon (1974) may apply in the specialized case of extremely dry cells.
Effects of sodium chloride on prevention of thermodormancy, ethylene and protein synthesis and respiration in Grand Rapids lettuce seeds
Authors: Small J. G. Chris , Gutterman Yitzdiak
Published: May 2006

Grand Rapids lettuce (Lactuca saliva L.) seeds entered into a state of secondary dormancy (thermodormancy) when they were imbibed at 40°C for 72 h. The effect of 40°C in inducing thermodormancy was largely reduced by imbibing seeds at 40°C in solutions of polyethylene glycol (PEG), mannitol and NaCl. Despite similar water potentials of solutions, NaCl pretreatment was more effective. Subsequent germination in the dark at 25°C of saline, high‐temperature‐pretreated seeds required only gibberellic acid (GA3), as was the case with nonthermodormant seeds. Thermodormancy reduced total respiratory capacity (VT) and increased the ratio of alternate pathway (Valt) to cytochrome pathway (Vcyt) respiration. This was prevented by saline pretreatment. Ethylene production and protein synthesis were depressed in thermodormant seeds, and this was partly alleviated by saline pretreatment. The patterns of protein synthesis in saline‐ and nonsaline‐freated seeds at 40°C were similar, differing only in that the saline treated seeds produced in addition a 78 kDa polypeptide. The pattern of protein synthesis at 40°C differed significantly from that at 25°C.
Induction of freezing tolerance in potato (Solanum commersonü) suspension cultured cells
Authors: Lee Stephen P. , Zhu Baolong , Chen Tony H. H. , Li Paul H.
Published: May 2006

The induction of freezing tolerance by abscisic acid (ABA) or cold treatment in suspension cultured cells of Solanum commersonii was studied. Both ABA (50–100 μM) at 23°C and low temperature (4°C) increased freezing tolerance in cultured Solanum commersonii cells from a LT50 (freezing temperature at which 50% cells were killed) of —5°C (control) to —11.5°C in 2 days. Cold‐induced freezing tolerance reached its maximum at 2 days and remained constant throughout the cold acclimation period of 11 days. The freezing tolerance induced by ABA, however, showed a rapid decline 2 to 5 days after initiation of ABA treatments. Addition of ABA (100 μM) to the culture medium at the inception of low temperature treatment did not enhance freezing tolerance of the cells beyond the level attainable by either treatment singly. Poly(A+)‐RNA was isolated from the respective treatments, translated in a rabbit reticulocyte lysate cell free system, and the translation products were resolved by two dimensional polyacrylamide gel electrophoresis (ID‐PAGE). Analysis of the in vitro translated products revealed changes in the abundance of approximately 26 products (encoding for polypeptides with M, of 14 to 69 kDa and pl of 4.90 to 6.60) in ABA‐treated cells 12 h after treatment, and 20 (encoding for polypeptides with Mr of 12 to 69 kDa, with pl of 4.80 to 6.42) in cells exposed to 4°C for 12 h. There were only 5 novel translation products observed when the ABA‐treated cells reached the highest level of freezing tolerance (2 days after the initiation of ABA treatment). Changes in translatable RNA populations during the induction of freezing tolerance in cells treated with either ABA or low temperature are discussed.
Phosphoenolpynivate carboxylase, malate and alcohol dehydrogenase activities in alfalfa (Medicago sativa) nodules under water stress
Authors: Irigoyen J. J. , Emerich D. W. , Sánchez‐Díaz M.
Published: May 2006

The effect of drought upon phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), malate ddiydrogenase (MDH; EC 1.1.1.37), alcohol dehydrogenase (ADH; EC 1.1.1.1) and β‐hydroxybulyrate dehydrogenase (β‐OH‐BDH; EC 1.1.1.30) enzyme activities as well as the leghemoglobin (Lb), malate and ethanol contents of alfalfa nodules (Medicago sativa L. cv. Aragon) were examined. Both the ieghemoglobin (Lb) content and the Lb/soluble protein ratio were significantly reduced at a nodule water potential (Ψnod) of—1.3 MPa. At lower Ψnod, Lb content decreased further, but the ratio remained unchanged. Slight stress (—1.3 MPa) drastically affected acetylene reduction activity (ARA; 60% reduction) whereas in vitro PEPC activity was main‐tained at relatively constant values. As stress progressed (—2.0 MPa), a simultaneous reduction in both activities was observed. Severe stress (Ψnod lower than —2.0 MPa) stimulated in vitro PEPC. Bacteroid β‐J‐OH‐BDH activity was stimulated by slight (—1.3 MPa) and moderate (—2.0 MPa) drought. MDH activity rose in slightly stressed nodules (Ψnod—1.3 MPa). Greater water deficits sharply decreased MDH activity to values significantly lower than those found in control nodules. Nodule malate content followed the same pattern as MDH. The plant fraction of the nodule showed constitutive ADH activity and contained ethanol. ADH was stimulated at slight (— 1.3 MPa) and moderate drought levels (—2.0 MPa). Ethanol content showed similar behavior to ADH activity. Inhibition of ARA, reduction of Lb content and stimulation of the fermentative metabolism induced by water stress suggest some reduction ira O2 availability within the nodule.
Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution
Authors: Irigoyen J. J. , Emerich D. W. , Sánchez‐Díaz M.
Published: May 2006

Exchange rates of CO2 and H2O and metabolism of hydrogen peroxide have been measured in leaves of alfalfa ev. Aragón) under drought stress. The inhibitory effect of drought upon photosynthesis depended on the severity of the stress treatment. Leaf water potential (Ψleaf) down to,‐2.8 MPa reduced CO2 availability due to stomatal closure and inhibited the rate of photosynthesis. Leaf water potential lower than,‐2.8 MPa directly affected CO2 fixation, although CO2 was not limiting. Transpiration was more affected by stornatal closure than photosynthesis, which led to am apparent improvement in WUE (water use efficiency). Alfalfa leaves with Ψleaf lower than,‐2.0 MPa had an increased quantum requirement, probably due to the severe stress effect on photoenergetic reactions.

Ethylene evolution from alfalfa leaves increased when they were subjected to Ψleaf of,‐ 1.6 MPa. Under more severe stress, the leaves showed low or almost no ethylene production. In parallel with the increase in ethyiene production, alfalfa leaves exhibited an increased membrane lipid peroxidation index (maloridialdehyde content) and an increased peroxide content. Superoxide disinutase activity (SOD; EC 1.15.1.1) was not affected by drought stress. Catalase (EC 1.11.1.6) was inhibited at slight stress, but significantly increased at a Ψleaf of ‐2.0 MPa. Peroxidase (EC 1.11.1.7) was progressively inhibited as drought stress developed. The possible implication of reactive O2 intermediates in drought stress‐induced senescence of alfalfa leaves is discussed in the light of the pattern of enzymatic scavenging systems.
The effect of phosphate deficiency on mitochondrial activity and adenylate levels in bean roots
Authors: Rychter Anna M. , Chauveau Michele , Bomsel Jean‐Loup , Lance Claude
Published: May 2006

Bean plants (Phaseolus vulgaris) were grown for 16–20 days with or without phosphate in Knop nutrient medium. It was found in previous experiments that for roots grown on a Pi‐deficient medium respiration is mainly carried out by the cyanide‐insensitive pathway. Mitochondria isolated from—Pi, roots had poor respiratory control and their respiration exhibited 62% inhibition by cyanide and was inhibited (30%) by salicylhydroxamic acid (SHAM). In contrast, mitochondria obtained with control (+Pi) roots had respiratory control and ADP/O ratios typical for succinate as the substrate; their respiration was inhibited to 95% by cyanide and insensitive to SHAM. The integrity of mitochondrial membranes was similar in both types of mitochondria. Cytochrome oxidase activity, however, was about 20% lower in ‐Pi mitochondria, but the cytochrome composition was the same in both types of mitochondria. The cytochrorae pathway was not operating at full capacity in mitochondria isolated from—Pi roots but the alternative oxidation pathway participated in a great part in mitochondrial respiration, similar to in vivo whole roots. The participation of the non‐phosphorylating., alternative pathway decreased the respiratory control ratio in mitochondria and had an effect on the total adenine nucleotide pool and energy charge values which were lower (16 and 13% respectively) in ‐Pi roots. About 50% lower ADP and 20% lower ATP levels were observed whereas AMP levels were several times higher.