bluuebunny/crossref_metadata_2025 huggingface dataset:
Osmoconditioning reduces physiological and biochemical damage induced by chilling in soybean seeds
Authors: Posmyk Malgorzata Maria , Corbineau Françoise , Vinel Dominique , Bailly Christophe , Côme Daniel
Published: March 2003

The aim of the present work was to investigate the effects of osmoconditioning on chilling injury in soybean (Glycine max (L.) Merr.) seeds during imbibition. Soybean seeds germinated readily over a large range of temperatures (10–35°C), the thermal optimum being 25–30°C. Low temperatures reduced the germination rate and no seed germinated at 1°C. Pre‐treatment of seeds at 1°C reduced further germination at the optimal temperature (25°C). This deleterious effect of chilling increased with duration of the treatment, and was maximal after 4 days. Osmoconditioning of seeds at 20°C with a polyethylene glycol‐8000 solution at −1.5 MPa for at least 24 h followed by drying back the seeds to their initial moisture content reduced their chilling sensitivity and even allowed germination at 1°C. Chilling of control seeds resulted in a sharp decline in in vivo ACC‐dependent ethylene production and in an increase in electrolyte leakage in the medium, which indicated deterioration of membrane properties. Osmoconditioned seeds placed at 1°C did not show any reduction in their ability to convert ACC to ethylene nor any strong increase in electrolyte leakage. Imbibition of both control and osmoconditioned seeds at 1°C resulted in a marked increase in ATP level (more than 50% of the total nucleotides) and energy charge; however, the latter cannot be considered as an indicator of chilling since it remained high (0.74–0.88) throughout the cold treatment. Chilling treatment longer than 6 days induced accumulation of malondialdehyde in the embryonic axis, which was more marked in control seeds than in osmoconditioned seeds, suggesting that chilling sensitivity was associated with lipid peroxidation. Imbibition of seeds at 1°C resulted in an increase in superoxide dismutase, catalase and glutathione reductase activity, which was generally higher in osmoconditioned seeds than in control ones. This stimulation of the antioxidant defence systems occurred during the 4 first days of chilling and decreased then in control seeds while it remained high in osmoconditioned ones. Re‐warming seeds at 25°C resulted in an increase in all enzyme activity involved in antioxidant defence. However this effect of re‐warming decreased in control seeds after 4 days of chilling, whereas it was maintained in osmoconditioned seeds.
Does elevated CO2 ameliorate the impact of O3 on chlorophyll content and photosynthesis in potato (Solanum tuberosum)?
Authors: Donnelly Alison , Craigon Jim , Black Colin R. , Colls Jeremy J. , Landon Geoff
Published: March 2003

This study examined the impact of season‐long exposure to elevated carbon dioxide (CO2) and ozone (O3), individually and in combination, on leaf chlorophyll content and gas exchange characteristics in potato (Solanum tuberosum L. cv. Bintje). Plants grown in open‐top chambers were exposed to three CO2 (ambient, 550 and 680 μmol mol−1) and two O3 treatments (ambient and elevated; 25 and 65 nmol mol−1, 8 h day−1 means, respectively) between crop emergence and maturity; plants were also grown in unchambered field plots. Non‐destructive measurements of chlorophyll content and visible foliar injury were made for all treatments at 2‐week intervals between 43 and 95 days after emergence. Gas exchange measurements were made for all except the intermediate 550 μmol mol−1 CO2 treatment. Season‐long exposure to elevated O3 under ambient CO2 reduced chlorophyll content and induced extensive visible foliar damage, but had little effect on net assimilation rate or stomatal conductance. Elevated CO2 had no significant effect on chlorophyll content, but greatly reduced the damaging impact of O3 on chlorophyll content and visible foliar damage. Light‐saturated assimilation rates for leaves grown under elevated CO2 were consistently lower when measured under either elevated or ambient CO2 than in equivalent leaves grown under ambient CO2. Analysis of CO2 response curves revealed that CO2‐saturated assimilation rate, maximum rates of carboxylation and electron transport and respiration decreased with time. CO2‐saturated assimilation rate was reduced by elevated O3 during the early stages of the season, while respiration was significantly greater under elevated CO2 as the crop approached maturity. The physiological origins of these responses and their implications for the performance of potato in a changing climate are discussed.
Leaf senescence in a non‐yellowing cultivar of chrysanthemum (Dendranthema grandiflora)
Authors: Reyes‐Arribas Trinidad , Barrett Jim E. , Huber Donald J. , Nell Terrill A. , Clark David G.
Published: March 2003

Chlorophyll (Chl) and total soluble protein decreased and proteolytic activity increased over a 12‐day period during dark‐induced senescence in detached leaves of Tara, a yellowing cultivar (Y) of Dendranthema grandiflora. In Boaldi, a non‐yellowing cultivar (NY), Chl and soluble protein remained near initial levels and little change in proteolytic activity was observed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins showed no major differences in banding patterns between the two cultivars at day 0; however, all of the resolved proteins were diminished in Tara by day 12. On the other hand, in NY Boaldi, the intensity of the protein bands did not change over the 12‐day period. Attached and detached leaves exhibited similar senescence patterns for each cultivar. Ethylene (100 μl l−1) accelerated the rate of Chl loss in detached leaves of Tara, but had no effect on Boaldi. These observations suggest that Boaldi is a stay‐green genotype, possibly a functional type. The results are discussed in relation to the role of ethylene in chrysanthemum leaf senescence.
Principles of redox control in photosynthesis gene expression
Authors: Pfannschmidt Thomas , Allen John F. , Oelmüller Ralf
Published: March 2003

Light is one of the most important environmental factors influencing gene expression in photosynthetic organisms. In particular, genes for components of the photosynthetic machinery show light‐dependent expression. In recent years, it has become clear that photosynthesis itself contributes important signals to this light control of gene expression by means of changes in the reduction/oxidation (redox) state of signalling molecules. Such changes in redox state are induced by changes in quality and quantity of the incident light. Redox signalling mechanisms therefore provide photosynthesis with the possibility of acclimational changes in the structure of the photosynthetic apparatus via a feedback control of photosynthesis gene expression. The great variety of these signalling mechanisms is summarised under the term ‘redox control’. In some cases, oxygen acts as a different environmental, light‐independent stimulus of photosynthetic gene expression, providing an additional redox signal and a different kind of redox control. In this review, we summarise present knowledge about such redox control mechanisms and analyse common properties as well as differences in the various signalling pathways. We suggest that there is an urgent need for a clear distinction between different kinds of redox control. Accordingly, we propose a categorisation into perceptional and transductional redox control. These categories are defined and examples given. The generalisation and comparability of results obtained in different physiological test systems and species are critically discussed.
Abiotic stress signal transduction in plants: Molecular and genetic perspectives
Authors: Xiong Liming , Zhu Jian‐Kang
Published: March 2003

Low temperature, drought and salinity are major adverse environmental factors that limit plant productivity. Understanding the mechanisms by which plants perceive and transduce these stress signals to initiate adaptive responses is essential for engineering stress‐tolerant crop plants. Molecular and biochemical studies suggest that abiotic stress signaling in plants involves receptor‐coupled phosphorelay, phosphoinositol‐induced Ca2+ changes, mitogen‐activated protein kinase cascades and transcriptional activation of stress‐responsive genes. In addition, protein posttranslational modifications and adapter or scaffold‐mediated protein‐protein interactions are also important in abiotic stress signal transduction. Most of these signaling modules, however, have not been genetically established to function in plant abiotic stress signal transduction. To overcome the scarcity of abiotic stress‐specific phenotypes for conventional genetic screens, molecular genetic analysis using stress‐responsive promoter‐driven reporter is suggested as an alternative approach to genetically dissect abiotic stress signaling networks in plants.
Effect of iron on activity of soybean multi‐subunit acetyl‐coenzyme A carboxylase
Authors: Plank David W. , Gengenbach Burle G. , Gronwald John W.
Published: March 2003

Multi‐subunit acetyl‐coenzyme A carboxylase (MS‐ACCase; EC 6.4.1.2) isolated from soybean chloroplasts is a labile enzyme that loses activity during purification. We found that incubating the chloroplast stromal fraction under anaerobic conditions or in the presence of 5 mM FeSO4 stimulated ACCase (acetyl‐CoA→malonyl‐CoA) and carboxyltransferase (malonyl‐CoA→acetyl‐CoA) activity. Fe‐stimulation of activity was associated with 59Fe binding to a stromal protein fraction. ACCase and carboxyltransferase activities measured in the stromal protein fraction containing bound 59Fe were 2‐fold and 6‐fold greater, respectively, than the control (stromal fraction not pretreated with FeSO4). Superose 6 gel filtration chromatography indicated 59Fe comigrated with stromal protein of approximately 180 kDa that exhibited carboxyltransferase activity, but lacked ACCase activity. Anion exchange (Mono‐Q) chromatography of the Superose 6 fraction yielded a protein peak that was enriched in carboxyltransferase activity and contained protein‐bound 59Fe. Denaturing gels of the Mono‐Q fraction indicated that the 180‐kDa protein was composed of a 56‐kDa subunit that was bound by an antibody raised against a synthetic β‐carboxyltransferase (β‐CTase) peptide. Incubation of the Mono‐Q carboxyltransferase fraction with increasing concentrations of iron at a fixed substrate concentration resulted in increased initial velocities that fit well to a single rectangular three parameter hyperbola (v=vo+Vmax[FeSO4]/Km+[FeSO4]) consistent with iron functioning as a bound activator of catalysis. UV/Vis spectroscopy of the partially purified fraction before and after iron incubation yielded spectra consistent with a protein‐bound metal cluster. These results suggest that the β‐CTase subunit of MS‐ACCase in soybean chloroplasts is an iron‐containing enzyme, which may in part explain its labile nature.
Plasticity of petioles of white clover (Trifolium repens) to blue light
Authors: Gautier Hélène , Varlet‐Grancher Claude , Membré Jeanne Marie
Published: March 2003

Petiole response of white clover to variations in blue light (BL) was studied on the main axis and on primary and secondary branches. The objectives of the present work were to determine (1) the time course of petiole response to BL and (2) whether these responses were dependent on petiole location. Under BL, clover had shorter petioles, and the switch to conditions without BL increased the length of forthcoming petioles. The fitting of a logistic function was used to compare the effect of BL on final petiole length, maximum elongation rate and the duration of petiole elongation between axes and phytomers. Petiole response to BL was not dependent on its location within the plant (axis type or phytomer position along the axis). A reduction in BL induced a rapid increase in leaf elongation rate, despite a small decrease in the duration of petiole elongation. Moreover, petiole response was dependent on petiole stage of development: the increase in the maximum rate of petiole elongation was inversely proportional to the petiole stage of development at the time of the switch. We conclude that the effects of BL on petiole elongation were not dependent on its position within the plant, whereas internode elongation resulted from the integration of light environment at the plant level. The difference between the responses of orthotropic and plagiotropic organs of clover to BL is discussed in relation to their structural function and localisation in the canopy.
Mitochondrial alternative oxidase acts to dampen the generation of active oxygen species during a period of rapid respiration induced to support a high rate of nutrient uptake
Authors: Yip Justine Y. H. , Vanlerberghe Greg C.
Published: March 2003

When wild type (wt) tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) suspension cells were grown under phosphate (P) limitation, they contained large amounts of mitochondrial alternative oxidase (AOX). When these cells were resupplied with P, there was a large, immediate and sustained stimulation of respiration to support a period of rapid P uptake. Two lines of evidence suggest that the abundant level of AOX present in wt cells contributed to this stimulated rate of respiration. First, when P‐limited transgenic antisense tobacco cells (AS8) lacking AOX were resupplied with P, the stimulation of respiration was much less dramatic even though these cells displayed similar rates of P uptake. Second, while the stimulated rate of respiration in AS8 cells was insensitive (as expected) to the AOX inhibitor n‐propyl gallate (nPG), much of the stimulated rate of respiration in wt cells could be inhibited by nPG. Given the non‐phosphorylating nature of AOX respiration, wt cells required higher rates of electron transport to O2 than AS8 cells to support similar rates of P uptake. The utilization of AOX by wt cells during P uptake was apparently not occurring because the cytochrome (Cyt) pathway alone could not fully support the rate of P uptake, as the respiration of cells lacking AOX (either untreated AS8 cells or wt cells treated with nPG) supported similar rates of P uptake as wt cells with abundant AOX. Rather, we provide in vivo evidence that the utilization of AOX during the period of high respiration supporting P uptake was to dampen the mitochondrial generation of active oxygen species (AOS).
Genes encoding chitinase‐antifreeze proteins are regulated by cold and expressed by all cell types in winter rye shoots
Authors: Pihakaski‐Maunsbach Kaarina , Moffatt Barbara , Testillano Pilar , Risueño Maria , Yeh Sansun , Griffith Marilyn , Maunsbach Arvid B.
Published: March 2003

One group of antifreeze proteins (AFPs) is composed of two chitinases that accumulate in the apoplast of winter rye leaves during cold acclimation. In this study, the 28‐ and 35‐kDa chitinase‐AFPs were localized in nonacclimated and cold‐acclimated rye leaves by immunoelectron microscopy with an antiserum produced against the purified winter rye 35‐kDa chitinase‐AFP. In cold‐acclimated winter rye leaves, labelled chitinase‐AFPs were abundant in the walls of epidermal, parenchymal sheath and mesophyll cells and xylem vessels, while less label was present in walls of vascular parenchyma cells. In contrast, chitinase labelling was essentially absent in the nonacclimated cells except in xylem vessels. As shown by RNA blotting, the transcripts of chitinase‐AFPs accumulated to a high level in rye leaves during cold acclimation, to a lesser extent in crowns and were not detectable in roots. mRNA transcripts of the 28‐kDa chitinase‐AFP were localized in rye leaves by in situ hybridization. The chitinase‐AFP transcripts were found in the same cell types as the protein itself. We conclude that all metabolically active cell types in cold‐acclimated winter rye leaves and crowns are able to synthesize chitinase‐AFPs and secrete them into adjacent cell walls, where they may interact with ice to delay its propagation through the plant and modify its growth.
Gibberellins in relation to flowering in Polianthes tuberosa
Authors: Chang Shuo‐Tsang , Chen Wen‐Shaw , Koshioka Masaji , Mander Lewis N. , Huang Kuang‐Liang , Du Bo‐Shiun
Published: March 2003

Endogenous gibberellins (GAs) in corms of Polianthes tuberosa L. (cv. Double) were isolated and identified by high performance liquid chromatography, bioassay and combined capillary gas chromatography‐mass spectrometry (GC‐MS). Gibberellins A1, A19, A20 and A53 were quantified at the vegetative, early floral initiation and flower development stages. The identification of 13‐hydroxylated GAs indicates the presence of the early 13‐hydroxylation pathway in P. tuberosa corms. An increase in GA1 and GA20, and a decrease in GA19 levels, coincided with the transition from the vegetative phase to the stages of early floral initiation and flower development. GA53 stayed at constant levels at the 3 different growth stages. The absence of GA1 in vegetative corms and its presence in corms at early floral initiation and flower development stages suggest that GA1 is a causal factor in inducing floral initiation in P. tuberosa. When GA1, GA3, GA4, GA20 and GA32 were applied to corms at the vegetative stage (plants about 5 cm in height), floral initiation was promoted by all of the GAs used, GA32 being the most active. In contrast with the other GAs, GA32 had no effect on stem elongation. Therefore, it is suggested that hydroxylated C‐19 GAs play an important role in flower induction in P. tuberosa.
Grain sink strength may be related to the poor grain filling of indica‐japonica rice (Oryza sativa) hybrids
Authors: Liang Jiansheng , Zhang Jianhua , Cao Xianzu
Published: March 2003

The physiological and biochemical factors contributing to poor grain filling of indica‐japonica rice (Oryza sativa L.) hybrids were studied by analyzing the role of grain sink strength in dry matter accumulation of grains of two types of rice cultivars, Yayou 2 (an indica‐japonica hybrid) and Yanjing 2 (a japonica cultivar). Carbon dioxide enrichment and plant hormone application were imposed at anthesis and the number of endosperm cells, dry matter accumulation and the activities of some sugar‐metabolizing enzymes of grains were measured during grain filling. In Yayou 2, strong‐potential grains (SPGs) accumulated dry weight much earlier than weak‐potential grains (WPGs), but this difference was not obvious for Yanjing 2. Carbon dioxide enrichment imposed after heading significantly stimulated dry matter accumulation of WPGs of Yayou 2, but had little influence on WPGs of Yanjing 2 and SPGs of both cultivars. Leaf sheath dry matter decreased steadily in both cultivars during early stages of grain filling and accumulated during the later stages. Carbon dioxide enrichment increased leaf sheath dry matter. Dry matter accumulated by grains was linearly related to the increases in endosperm cell numbers and the activities of sucrose synthase (SS) and ADP‐glucose pyrophosphorylase (AGPase) in SPGs and WPGs of both cultivars. Application of either 6‐benzyladenine or abscisic acid had no significant influences on both endosperm cell number and grain dry matter accumulation. These results suggest that grain sink strength, determined by both cell numbers, SS and AGPase activities in the endosperm control the dry matter accumulation of grains.
Cloning and sequence analysis of cDNA encoding thiamin‐binding proteins from sesame seeds
Authors: Watanabe Katsumi , Takahashi Hideyuki , Mitsunaga Toshio
Published: March 2003

The amino acid sequences of the large polypeptides of thiamin‐binding proteins (TBPs) from sesame (Sesamum indicum L.) seeds (STBP‐I, ‐II and ‐III) were analyzed. The large polypeptides of STBP‐I, ‐II and ‐III had the same amino acid sequences as did their small polypeptides. The peptide sequence information obtained from STBPs was used to synthesize DNA primers for amplification of the gene(s) encoding STBPs. A 200‐bp fragment was amplified from cDNA synthesized from RNA from sesame seeds 4 weeks after flowering. The 200‐bp fragment was used to clone full‐length cDNA(s) encoding STBP(s) with RACE techniques. A 644‐bp fragment was amplified, cloned and sequenced. The cDNA was a full‐length clone encoding STBP(s). It contained an open reading frame, which defined a 143‐residue polypeptide. The identified small and large polypeptide sequences of STBPs exactly matched the sequence encoded within the cDNA clone. These results indicated that the small and large polypeptides of STBPs were encoded on the mRNA as a single large proprotein precursor and that the final mature forms were generated by post‐translational processing in the same manner as the other 2S albumins of plant seeds.
Involvement of polyamines in the control of fruitlet physiological abscission in grapevine (Vitis vinifera)
Authors: Aziz Aziz , Brun Oliver , Audran Jean‐Claude
Published: March 2003

The potential contribution of polyamines (PAs) in the regulation of physiologically induced fruitlet abscission was investigated in cuttings from two cultivars of Vitis vinifera L., Pinot noir (PN) and Merlot (MRT). Abscission was higher in MRT than in PN and was preceded by a decrease in free PA levels. This decline was more pronounced in inflorescences than in leaves of the sensitive cultivar. Soluble conjugated PA showed an opposite trend in both cultivars. This suggests a cause‐effect relationship between free and/or conjugated PA levels in floral organs and susceptibility to abscission. Spermidine (Spd), but not putrescine (Put) or diaminopropane, supplied at 0.5–1 mM to the nutritive medium prior to the anthesis, increased free and conjugated PA levels in the inflorescences and markedly inhibited abscission. α‐Difluoromethylarginine, an inhibitor of arginine decarboxylase, but not α‐difluoromethylornithine, an inhibitor of ornithine decarboxylase, lowered PA levels and increased abscission. Treatment with cyclohexylamine or β‐hydroxyethylhydrazine as potent inhibitors of Spd synthase and PA oxidases, respectively, reduced the Spd and/or spermine levels and enhanced free Put in the inflorescences, inducing an increased abscission of floral organs shortly after anthesis. These data suggest that PAs, particularly Spd, could be involved in the regulation of grapevine fruitlet physiological abscission.
Role of glutathione in adaptation and signalling during chilling and cold acclimation in plants
Authors: Kocsy Gábor , Galiba Gábor , Brunold Christian
Published: March 2003

Glutathione is an important component of the ascorbate‐glutathione cycle, which is involved in the regulation of hydrogen peroxide (H2O2) concentrations in plants. During chilling and cold acclimation, i.e. exposure to temperatures between 0 and 15°C, H2O2may accumulate. Excess electrons from the photosynthetic and respiratory electron transport chains can be used for the reduction of oxygen, thus producing superoxide radicals (O2⋅−); these are subsequently transformed to H2O2via superoxide dismutase (SOD; EC 1.15.1.1). During the removal of excess H2O2, reduced glutathione (GSH) is converted to its oxidised form (GSSG), and GSH is regenerated by the activity of NADPH‐dependent glutathione reductase (GR; EC 1.6.4.2). At low non‐freezing temperatures, high GSH content and GR activity were detected in several plant species, indicating a possible contribution to chilling tolerance and cold acclimation. Changes in H2O2concentration and GSH/GSSG ratio alter the redox state of the cells and may activate special defence mechanisms through a redox signalling chain. The finding that several defence genes have antioxidant responsive elements or GSSG binding sites in their regulatory regions supports the idea that redox signalling is involved in regulating gene expression in response to low temperature.
Endogenous levels of polyamines in the organs of cucumber plant (Cucumis sativus) and factors affecting leaf polyamine contents
Authors: Fujihara Shinsuke , Yoneyama Tadakatsu
Published: March 2003

Polyamine compositions of various organs from hydroponically cultivated cucumber plants (Cucumis sativus L. cv. Sharp‐1) and factors affecting the leaf polyamine content were examined. Diamine putrescine was found most abundantly in the root, while a relatively large amount of spermine was detected in the reproductive organs such as the immature fruit and the calyx (+stamen). Spermidine was present at the highest level in rapidly growing tissues such as newly expanded leaf and fruit at an early developing stage, implying the possible involvement of spermidine in the growth and development of these young tissues. Polyamine content of cucumber leaves changed during the day. Especially, the putrescine content of upper leaves showed a striking decrease from the morning to the night. Alterations of leaf Ca or Mg content did not significantly affect leaf polyamine composition. On the other hand, abnormal cucumber leaves showed altered polyamine composition. Yellowing of the leaf intervein resulted in a striking decrease in spermidine content without a significant change in putrescine and spermine content. By contrast, the leaves infected with the phytopathogen, powdery mildew, showed decreased putrescine and increased spermine content in response to the degree of fungi infection. The possible usefulness of polyamines as a diagnostic marker of plant development and physiological disorder is discussed.
The effect of AOA on ethylene and polyamine metabolism during early phases of somatic embryogenesis in Medicago sativa
Authors: Huang Xue‐Lin , Li Xiao‐Ju , Li Yin , Huang Long‐Zhou
Published: March 2003

Changes in the levels of ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (MACC) and polyamines were simultaneously investigated during the early phases of alfalfa somatic embryogenesis. These included the period of induction and subculture of callus, and 3‐ and 7‐day suspension cultures for the induction of somatic embryogenesis. The polyamines contained in the embryogenic callus were found to include putrescine (Put), spermidine (Spd) and spermine (Spm), but the level of Spm was much less than that of Put and Spd. There was a dramatic increase in MACC after induction of embryogenesis, and ACC levels were lower in somatic embryos than in embryogenic callus. Induction of embryogenesis for 3 days increased the levels of ACC and polyamines to a maximum level, and these then reduced as the embryogenesis proceeded. The ratios of Put/Spd and ACC/MACC were decreased during the induction. This indicated that both high levels of ACC and polyamines might be a prerequisite for early differentiation during the induction of the embryogenesis. Thus, there appears not to be competition between polyamine biosynthesis and ethylene biosynthesis at least during the induction of somatic embryogenesis, because both the polyamines and ACC were simultaneously increased during the induction period. Conversion of ACC into MACC and the maintenance of a relatively high level of polyamines, especially Spd, appear to be important for further development of the embryos.  When aminooxylvinylglycine (AOA) was added at the initiation of the callus subculture, it had no significant effect on the callus growth, the ethylene production and ACC level of the callus. However, AOA increased the numbers of the embryos accompanying an increase in Spd level and S‐adenosylmethionine decarboxylase (SAMDC) activity. Thus, the AOA effect could be associated with Spd increase rather than with the effect of ethylene biosynthesis.
Ammonium induction of a novel isoform of glucose‐6P dehydrogenase in barley roots
Authors: Esposito Sergio , Massaro Graziella , Vona Vincenza , Di Martino Rigano Vittoria , Carfagna Simona , Rigano Carmelo
Published: March 2003

The effects of ammonium and glutamine supply on amino acid levels and the activity of glucose‐6P dehydrogenase (G6PDH EC 1.1.1.49), the main regulated enzyme of the oxidative pentose phosphate pathway, were investigated in barley roots (Hordeum vulgare cv. Alfeo). Feeding ammonium to barley plants increased the contents of glutamine, asparagine and G6PDH in roots. These effects were abolished by using inhibitors of glutamine synthetase. Glutamine‐fed barley roots showed a similar increase in G6PDH activities to ammonium‐fed plants. Two G6PDH enzymes (G6PDH 1 and 2) were partially purified and characterized from ammonium‐fed and glutamine‐fed roots. The isozymes had different pH optima and apparent Km values for glucose‐6P. G6PDH 2 showed similar kinetic parameters to the G6PDH present in root extracts of barley grown without any nitrogen source, while G6PDH 1 exhibited different kinetic parameters, suggesting the appearance of a second G6PDH isoform in response to ammonium. Western blot analysis demonstrated the existence of two G6PDH subunits of different molecular mass in barley roots grown in the presence of ammonium or glutamine, while only one isoform could be detected in roots grown without any nitrogen source. The results suggest a primary role of ammonium and/or glutamine in the appearance of a novel G6PDH isoform; this enzyme (G6PDH 1) shows kinetic parameters similar to those measured previously for chloroplastic and plastidic isoforms and seems to be induced by changes in glutamine content or a related compound(s) in the roots.
Biochemical characterisation of esterases active in hydrolysing xenobiotics in wheat and competing weeds
Authors: Cummins Ian , Burnet MichaeI , Edwards Robert
Published: March 2003

Esterase activities toward model xenobiotic substrates (p‐nitrophenyl acetate, naphthyl acetate) and pesticide esters (diclofop methyl, bromoxynil octanoate, binapacryl) have been compared in crude extracts from wheat (Triticum aestivum L.) and Triticum progenitors of wheat. Esterase activities were also determined in the weeds, wild oat (Avena fatua) and two populations of black‐grass (Alopecurus myosuroides), one of which (Rothamsted) is susceptible to herbicides, while the other (Peldon) shows cross‐resistance to multiple classes of herbicides. Esterase activity toward the model substrates was highest in wheat, while the weeds were more active in hydrolysing the pesticides. Using isoelectric focussing (pH 4–8), 13 proteins with esterase activity toward α‐naphthyl acetate could be resolved in hexaploid wheat (genome AABBDD). The pattern of these activities was most similar to that of the diploid progenitor T.tauschii (DD), excepting a major acidic esterase (pI 4.6), which originated from T. urartu (AA). Resolved esterase activities in the weeds were distinct from those observed in the Tritcum species. However, unlike the case with other classes of xenobiotic‐metabolising enzymes, the complement of esterases in the Peldon and Rothamsted populations of black‐grass appeared to be identical. In all species, the more basic esterases (>pI 5.0) were sensitive to inhibition by organophosphate and carbamate insecticides, suggesting that they were B‐class esterases. In contrast, the acidic wheat esterase (pI 4.6) with the greatest activity toward α‐naphthyl acetate was insensitive to insecticides. This wheat‐specific esterase was purified 7000‐fold by a combination of hydrophobic interaction chromatography, gel filtration and anion‐exchange chromatography. The purified esterase behaved as a monomeric 45‐kDa protein showing high activity toward p‐nitrophenyl acetate and α‐naphthyl acetate, but limited activity toward the pesticides.
Changes in superoxide dismutase activity and photosynthetic pigment content during growth of marine phytoplankters in batch‐cultures
Authors: Sigaud‐Kutner T. C. S. , Pinto E. , Okamoto O. K. , Latorre L. R. , Colepicolo P.
Published: March 2003

The ability of phytoplankton to cope with oxidative stress is one of the main factors that influence its survival in the marine environment, when senescence conditions prevail. In a first attempt to investigate the antioxidant strategies of different phytoplanktonic groups face to oxidative stress, the superoxide dismutase (SOD; EC 1.15.1.1) activity and photosynthetic pigment content along the growth curves of the dinoflagellate Lingulodinium polyedrum (Stein) Dodge, the prasinophycean Tetraselmis gracilis (Kylin) Butcher and the diatom Minutocellus polymorphus (Hargraves and Guillard) Hasle, von Stosch and Syvertsen were evaluated in batch‐cultures. Total SOD activity was determined by an indirect method involving the inhibition of cytochrome c reduction. The contents of photosynthetic pigments were analysed by HPLC using a reverse phase column (RP‐18), based on a ternary gradient. A peak of total SOD activity was detected at the beginning of the T. gracilis and M. polymorphus exponential growth. In L. polyedrum and M. polymorphus, SOD activity increased approximately three times by day 17 of growth, compared to the values obtained on day 3 (exponential phase) of the growth curve. All three species of microalgae had reduced SOD activity at the end of their growth. The levels of peridinin in L. polyedrum increased about 60% by day 17 of growth compared to the values obtained at exponential phase. Tetraselmis gracilis exhibited a remarkable increase (approximately 85%) in β‐carotene concentration after 10–14 days of growth whereas the β‐carotene levels in M. polymorphus decreased about 85% along its growth curve. These findings suggest that the antioxidant response during senescence in batch‐cultures differ according to the species. Induction of SOD activity may occur either in the early exponential or stationary growth phases, which is important to prevent oxidative stress triggered by a number of factors that affects growth, such as nutrient and light availability.
Regulation of frost resistance during cold de‐acclimation and re‐acclimation in oilseed rape. A possible role of PSII redox state
Authors: Rapacz Marcin
Published: March 2003

A possible role of photosynthetic apparatus during cold de‐acclimation was studied in oilseed rape (Brassica napus var. oleifera). Plants of spring (Star) and winter (Górczañski) cultivars were cold acclimated at + 5°C, and de‐acclimated during 4 weeks at combinations of + 12 and + 20°C operating in the light or/and dark, with a 12‐h photoperiod. Evidence is presented that the photosynthetic apparatus may be involved in temperature perception during de‐acclimation. De‐acclimation was faster under a 20/12°C (day/night) treatment than under the reverse 12/20°C (day/night). De‐acclimation rate was constant when the day temperature was constant, irrespective of the night temperature both under cold day temperature regimes (12/20, 12/12°C (day/night) and warm‐day treatments (20/12, 20/20°C (day/night). The fast decrease in frost resistance observed under warm‐day de‐acclimation was always accompanied by an acceleration of elongation growth. In the spring cultivar, elongation growth increased starting from the second week of de‐acclimation, regardless of temperature conditions. Once elongation growth had commenced during de‐acclimation, it continued throughout the period necessary for re‐acclimation to low temperature. Re‐acclimation to the initial freezing tolerance level was only possible when plant elongation was reduced. In addition re‐acclimation of the photosynthetic apparatus to low temperature was impossible in fast growing plants. A possible relationship between PSII, growth rate and frost resistance during cold acclimation and de‐acclimation is discussed.
Carbon assimilation, partitioning and export in mature cladophylls of two asparagus (Asparagus officinalis) cultivars with contrasting yield
Authors: Guo Jianmin , Jermyn William A. , Turnbull Matthew H.
Published: March 2003

To assess the physiological aspects underpinning cultivar difference in asparagus (Asparagus officinalis L.) yield, diel carbon exchange, carbon partitioning and export and sucrose phosphate synthase (SPS) activity were examined in mature cladophyll tissue of two asparagus cultivars (ASP‐69 and ASP‐03) under field conditions. Both cultivars exhibited similar diel patterns in carbon exchange rate (CER) and carbohydrate partitioning. Rates of carbon export estimated from CER and dry mass changes were the highest at midday and coincided with maximum assimilation rate. Carbon export accounted for about 74% of carbon fixation during the photoperiod. No diel fluctuations were observed in SPS activity in either cultivar. A positive correlation between day CER and carbon export rate (r2 = 0.87) was found and this relationship did not differ between the two cultivars studied. The greater carbon export rate measured in the high‐yielding cultivar (ASP‐69) was associated with significantly higher CER in comparison to the low‐yielding cultivar (ASP‐03). However, a correlation between sucrose concentration and carbon export rate did not exist. Biochemical evidence indicated that the greater CER in ASP‐69 was associated with a significantly greater SPS activity (P  0.05). Phloem 14C exudate analysis revealed that 14C flux out of cladophyll tissue in ASP‐69 was significantly greater than in ASP‐03. These results indicate a feed‐forward effect of rate of photosynthesis on assimilate export in the two cultivars studied.
Oxidative metabolism and the physiological age of seed potatoes are affected by increased α‐linolenate content
Authors: Zabrouskov Vladimir , Kumar G.N. Mohan , Spychalla James P. , Knowles N. Richard
Published: March 2003

The effects of high α‐linolenate content on lipid peroxidation, oxidative stress and loss of plant growth potential during ageing of potato (Solanum tuberosum L.) seed‐tubers was examined. Endoplasmic reticulum (FAD3) and plastidal (FAD7) 18:2 fatty acid desaturases were upregulated in potato (cv. Desiree), resulting in a 2‐fold average increase in mol percentage 18:3 in the total lipid fraction across all transgenic clones. In double‐transformed (FAD3+7) tubers, high α‐linolenate phenotype effected accelerated ageing, resulting in growth responses characteristic of older seed‐tubers. Although respiration rates of wild‐type (WT) and FAD3+7 tubers were equal at 7 months of storage, rates had increased by 23% and 50% in WT and FAD3+7 tubers, respectively, by 19 months of storage. Electrolyte leakage of tissue from 19‐month‐old FAD3+7 tubers was significantly greater than that from WT tubers of the same age, indicating that the high α‐linolenate phenotype was detrimental to membrane integrity during long‐term storage. On average, indices of lipid peroxidation (malondialdehyde, ethane, C‐6 aldehydes) were higher in older FAD3+7 tubers, relative to WT tubers. Activities of glucose‐6‐phosphate dehydrogenase, peroxidase, glutathione reductase, ascorbate peroxidase and monodehydroascorbate reductase increased in tubers with advancing age and were higher, on average, in FAD3+7 tubers. Dehydroascorbate reductase activity decreased with age, with no difference between transgenic and WT lines. Collectively, these results indicate that FAD3+7 tubers underwent a higher degree of oxidative stress during ageing. The age‐induced increase in respiration of FAD3+7 tubers was at least partly a response to fuel increased free radical scavenging through the ascorbate‐glutathione antioxidant pathway. By affecting the susceptibility of lipids to peroxidation, the degree of fatty acid unsaturation influenced the development of oxidative stress and the overall rate at which growth potential was lost from seed‐tubers during ageing. Thus, oxidative stress plays an integral role in modulating the ageing process to affect growth potential from potato seed‐tubers.
Wheat catalase expressed in transgenic rice can improve tolerance against low temperature stress
Authors: Matsumura Takeshi , Tabayashi Noriko , Kamagata Yasuyo , Souma Chihiro , Saruyama Haruo
Published: March 2003

We examined whether the expression of wheat catalase (EC 1.11.1.6) cDNA in transgenic rice (Oryza sativa L.) could enhance tolerance against low temperature injury. Transgenic rice plants expressing wheat CAT protein showed an increase of activities in leaves at 25°C, 2‐ to 5‐fold that in non‐transgenic rice. At 5°C, catalase activities were about 4–15 times higher than those in non‐transgenic rice were. A comparison of damage observed in leaves as they withered due to chilling at 5°C showed that transgenic rice displayed an increased capability to resist low temperature stress. The exposure of these plants to low temperature at 5°C for 8 days resulted in decreased catalase activities in leaves at 25°C, but the transgenic plants indicated 4 times higher residual catalase activities than those of non‐transgenic ones. The concentration of H2O2 in leaves was kept lower in transgenic rice than that of the control plants during the 8 days chilling. These results suggest that the improved tolerance against low temperature stress in genetically engineered rice plants be attributed to the effective detoxification of H2O2 by the enhanced catalase activities.
Programmed cell death induced by (β‐d‐galactosyl)3 Yariv reagent in Nicotiana tabacum BY‐2 suspension‐cultured cells
Authors: Chaves Inês , Regalado Ana Paula , Chen Ming , Ricardo Cândido Pinto , Showalter Allan M.
Published: March 2003

Programmed cell death (PCD) is involved in plant development and pathogen defence and can be triggered in vitro by several biotic and abiotic stimuli. In this report (β‐d‐galactosyl)3 Yariv reagent, a chemical that specifically binds to arabinogalactan‐proteins (AGPs), completely inhibited cell growth and induced PCD in tobacco BY‐2 suspension cultured cells. Analysis of DNA from these cells, by agarose gel electrophoresis, revealed a DNA ladder consisting of multimers of 140–170 bp, similar to apoptotic animal DNA internucleosomal fragmentation. Complementary morphological studies revealed additional PCD characteristics in the Yariv‐treated BY‐2 cells, including cell shrinkage and cytoplasmic condensation. These studies demonstrate the usefulness of BY‐2 cells as a model plant PCD system and confirm a link between AGPs and PCD.
Photoperiodic control of growth, cold acclimation and dormancy development in silver birch (Betula pendula) ecotypes
Authors: Li Chunyang , Junttila Olavi , Ernstsen Arild , Heino Pekka , Palva E. Tapio
Published: March 2003

Survival and growth of temperate zone woody plants under changing seasonal conditions is dependent on proper timing of cold acclimation and development of vegetative dormancy, shortening photoperiod being an important primary signal to induce these adaptive responses. To elucidate the physiological basis for climatic adaptation in trees, we have characterized photoperiodic responses in the latitudinal ecotypes of silver birch (Betula pendula Roth) exposed to gradually shortening photoperiod under controlled conditions. In all ecotypes, shortening photoperiod triggered growth cessation, cold acclimation and dormancy development, that was accompanied by increases in endogenous abscisic acid (ABA) and decreases in indole‐3‐acetic acid (IAA). There were distinct differences between the ecotypes in the rates and degrees of these responses. The critical photoperiod and the photoperiodic sensitivity for growth cessation varied with latitudinal origin of the ecotype. The northern ecotype had a longer critical photoperiod and a greater photoperiodic sensitivity than the southern ecotype. Compared with the southern ecotypes, the northern ecotype was more responsive to shortening photoperiod, resulting in earlier cold acclimation, dormancy development, increase in ABA content and decrease in IAA content. However, at the termination of the experiment, all the ecotypes had reached approximately the same level of cold hardiness (−12 to −14°C), ABA content (2.1–2.3 µg g−1 FW) and IAA content (17.2–20.3 ng g−1 FW). In all ecotypes, increase in ABA levels preceded development of bud dormancy and maximum cold hardiness. IAA levels decreased more or less parallel with increasing cold hardiness and dormancy, suggesting a role of IAA in the photoperiodic control of growth, cold acclimation and dormancy development in birch.
Short‐term boron deprivation enhances levels of cytoskeletal proteins in maize, but not zucchini, root apices
Authors: Yu Qin , Baluška František , Jasper Fred , Menzel Diedrik , Goldbach Heiner E.
Published: March 2003

By using indirect immunofluorescence microscopy and Western blot analysis, we have demonstrated increased levels of actin and tubulin proteins as well as an altered polymerization pattern of their cytoskeletal assemblies in maize, but not zucchini root apices, as a response to early boron deprivation. Northern blot analysis, however, did not show significant increases in the amount of steady‐state mRNAs of actin and tubulin. This finding indicates that these rapid cytoskeletal responses to boron removal are very likely regulated at translational/post‐translational levels. Interestingly, these increased levels of cytoskeletal proteins coincided well with a reduction in the water‐extractable, but not with the cell wall‐bound, fraction of boron. This implicates that free boric acid, or other more labile boron complexes, might be involved in the activation of cytoskeletal responses in maize root apices. In fact, our experimental approach revealed that maize was suffering from boron deprivation as early as zucchini. This was evidenced by its slightly reduced root elongation rate recorded within 3–5 h of boron deprivation. Importantly, however, maize roots can recover from this early inhibition indicating an effective adaptation mechanism. In contrast, zucchini roots apparently lack this boron‐deprivation response pathway and suffer extensively when exposed to boron‐free environment. This leads to the tentative working hypothesis for an adaptive mechanism of maize roots to boron deprivation by enhancing its cytoskeletal protein levels and altering their polymerization patterns in order to mechanically reinforce the cell periphery complex of their cells. This testable hypothesis requires further experimental verification.
Transporter gene families in plants: the sulphate transporter gene family — redundancy or specialization?
Authors: Hawkesford Malcolm J.
Published: March 2003

Analysis of the Arabidopsis genome has indicated that the gene families encoding for specific solute transporters are surprisingly large. An example is the sulphate transporter family, which in Arabidopsis, consists of 14 isoforms showing homology to one another. H+‐sulphate co‐transport has been demonstrated for some, but not all, of these Arabidopsis isoforms. Occurrence of the sulphate transporter is ubiquitous and many examples have been cloned from a variety of plant species, animals and yeast. This is a unique transporter family with no apparent homology to any other transporter type. Phylogenetic analysis of the plant gene or amino acid sequences indicates that there are 5 or more distinguishable clusters within the family of sulphate transporters. Analysis of functional characteristics and patterns of regulation together with localization data, suggests that these groups have specific roles, such as high affinity uptake in the root, translocation in vascular tissues and cell to cell transfer in leaves and seeds. Additionally, some members of this sulphate transporter family may have discrete subcellular locations in plastid or tonoplast membranes. Within individual groups, there are often multiple isoforms from the same species, indicating an even greater degree of specialization or alternatively, redundancy. This mini‐review will summarize the available data to distinguish between specialization and redundancy.
Antiviral drug resistance in human cytomegalovirus
Authors: Chou S.
Published: March 2003

Drug‐resistant cytomegalovirus (CMV) should be considered when viral shedding persists after several weeks of therapy. The problem is most likely to arise in the setting of a severely immunosuppressed host with continuing or relapsing disease. Not all treatment failure can be attributed to drug resistance. The testing of CMV isolates for drug resistance in cell culture is time‐consuming and labor‐intensive, but recent advances in understanding of the genetics of resistance have resulted in rapid genotypic assays for specific mutations in the viral UL97 phosphotransferase or UL54 DNA polymerase genes that can predict resistance and cross‐resistance to specific drugs. This information may help in the selection of alternative therapy Note.