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Osmotic Adjustment (osmotic + adjustment)
Selected AbstractsSolute Heterogeneity and Osmotic Adjustment in Different Leaf Structures of Semi-Leafless Pea (Pisum sativum L.) Subjected to Water StressPLANT BIOLOGY, Issue 5 2002E. M. González Abstract: Semi-leafless varieties of pea have considerable agronomic importance and it has been suggested that they may have a superior response to water deficits than conventional varieties. However, these varieties are poorly characterized from a physiological point of view and there is lack of a physiological basis for their supposed better performance under conditions of water deficit. Here, we describe the solute distribution in the different leaf structures of a semi-leafless pea variety (Pisum sativum L.) under non-limiting water conditions and under water stress. A conventional variety was subjected to the same conditions for comparative purposes. A detailed study was carried out both at the tissue level and at the single cell level. In control conditions, epidermal vacuoles of tendrils showed a different ion distribution of those of the laminar leaf structures. However, under water deficit, only stipules of the semi-leafless variety showed a significantly higher capability to increase osmolarity. This occurred by accumulating potassium, magnesium and chloride to a higher extent than other leaf structures. The inability of performing an adequate osmotic adjustment in tendrils may be the cause of the lack of a better response to water deficit. [source] Physiological responses of lupin genotypes to terminal drought in a Mediterranean-type environmentANNALS OF APPLIED BIOLOGY, Issue 3 2007J.A. Palta Abstract Field experiments concerning lupin grown in a low-rainfall environment of the Mediterranean climatic region of Western Australia were conducted over three seasons to identify and evaluate the characteristics that maximise yield per unit of rainfall. The characteristics of early flowering and podding, high pod retention, fast rates of seed filling, osmotic adjustment and the degree of dry matter transfer from stem to the seed were studied in 12 lupin genotypes differing in seed yield under conditions of terminal drought. To allow recently released cultivars and advanced breeding lines to be evaluated, five to six genotypes were included in the first and the third year and nine in the second year. The genotypes were grown rainfed until pod set and then under a rainout shelter. Flowering and podding dates, pod retention, seed growth rate and osmotic adjustment were measured in detail, together with leaf water potential, seed yield and its components. The timing and intensity of development of the terminal drought varied from average in 1998 and 1999 to extreme in 2000. In each year, the seed yield under terminal drought showed genotypic differences, which appeared consistent with the timing and intensity of the development of terminal drought. Early flowering and podding were significantly correlated with seed yield. Fast rates of seed growth were highly and significantly correlated with high yields regardless of the intensity of development of terminal drought. Pod retention was highly correlated with yield in seasons in which the intensity of the development of terminal drought was average but not under extreme conditions of terminal drought. This was because the seed number per pod was markedly reduced to compensate for the high number of pods retained. Osmotic adjustment did not occur during the development of terminal drought in any of the genotypes. Dry matter transfer from stems to seeds was insignificant and not related to seed yield, suggesting that it is not a useful characteristic in screening for high yield under terminal drought. [source] Osmotic adjustment of chickpea (Cicer arietinum) is not associated with changes in carbohydrate composition or leaf gas exchange under droughtANNALS OF APPLIED BIOLOGY, Issue 2 2007P.S. Basu Abstract Genetic differences in osmotic adjustment (OA) have been reported among chickpea (Cicer arietinum) cultivars. In this study eight advanced breeding lines (ABLs) derived from a cross between CTS 60543 (high OA) and Kaniva (low OA) and Tyson (medium OA) and Kaniva, along with the parents, were evaluated for OA, leaf carbohydrate composition and leaf gas exchange under dryland field conditions in India. The water potential (WP) decreased to lower values (less than ,2.5 MPa) in Tyson, M 110 and M 86 than in the other genotypes. With decrease in WP, OA increased by 0.5 MPa in Kaniva and CTS 60543 to 1.3 MPa in M 55. As the decrease in WP varied with genotype, when OA was regressed against WP M 39 and M 55 had greater increases in OA with decrease in WP than the remaining nine genotypes, including the parents. As WP decreased, leaf starch content decreased while total soluble sugars, hexoses and sucrose increased: the decrease in starch was much smaller in M 93 and M 129 than in Tyson and M 51, but genotypic differences could not be detected in the increase in total sugars, hexoses or sucrose. The rates of photosynthesis and transpiration decreased as the WP became more negative, but M 129 reached low rates of photosynthesis (2 ,mol m,2 s,1) and transpiration at a WP of ,1.7 MPa, whereas Tyson reached the same low rate at ,2.4 MPa. While OA varied among the chickpea genotypes, the differences were not associated with the changes in carbohydrate composition or the rates of gas exchange at low values of WP. Further, the degree of OA of the 11 genotypes was not the same as when they were selected for differences in OA under rainout shelter conditions in the field in Australia, suggesting that OA may show poor stability depending upon the stress level, location or physiological stage of the plant. This suggests that OA is not a valuable drought-resistance trait to select for in chickpea breeding programmes. [source] Ion transport and osmotic adjustment in Escherichia coli in response to ionic and non-ionic osmoticaENVIRONMENTAL MICROBIOLOGY, Issue 1 2009Lana Shabala Summary Bacteria respond to osmotic stress by a substantial increase in the intracellular osmolality, adjusting their cell turgor for altered growth conditions. Using Escherichia coli as a model organism we demonstrate here that bacterial responses to hyperosmotic stress specifically depend on the nature of osmoticum used. We show that increasing acute hyperosmotic NaCl stress above ,1.0 Os kg,1 causes a dose-dependent K+ leak from the cell, resulting in a substantial decrease in cytosolic K+ content and a concurrent accumulation of Na+ in the cell. At the same time, isotonic sucrose or mannitol treatment (non-ionic osmotica) results in a gradual increase of the net K+ uptake. Ion flux data are consistent with growth experiments showing that bacterial growth is impaired by NaCl at the concentration resulting in a switch from net K+ uptake to efflux. Microarray experiments reveal that about 40% of upregulated genes shared no similarity in their responses to NaCl and sucrose treatment, further suggesting specificity of osmotic adjustment in E. coli to ionic and non-ionic osmotica. The observed differences are explained by the specificity of the stress-induced changes in the membrane potential of bacterial cells highlighting the importance of voltage-gated K+ transporters for bacterial adaptation to hyperosmotic stress. [source] Compatible solutes of organisms that live in hot saline environmentsENVIRONMENTAL MICROBIOLOGY, Issue 9 2002Helena Santos Summary The accumulation of organic solutes is a prerequisite for osmotic adjustment of all microorganisms. Thermophilic and hyperthermophilic organisms generally accumulate very unusual compatible solutes namely, di- myo -inositol-phosphate, di-mannosyl-di- myo -inositol-phosphate, di-glycerol-phosphate, mannosylglycerate and mannosylglyceramide, which have not been identified in bacteria or archaea that grow at low and moderate temperatures. There is also a growing awareness that some of these compatible solutes may have a role in the protection of cell components against thermal denaturation. Mannosylglycerate and di-glycerol-phosphate have been shown to protect enzymes and proteins from thermal denaturation in vitro as well, or better, than compatible solutes from mesophiles. The pathways leading to the synthesis of some of these compatible solutes from thermophiles and hyperthermophiles have been elucidated. However, large numbers of questions remain unanswered. Fundamental and applied interest in compatible solutes and osmotic adjustment in these organisms, drives research that, will, in the near future, allow us to understand the role of compatible solutes in osmotic protection and thermoprotection of some of the most fascinating organisms known on Earth. [source] Physiological and morphological responses of the soil bacterium Rhodococcus opacus strain PD630 to water stressFEMS MICROBIOLOGY ECOLOGY, Issue 2 2004Héctor M. Alvarez Abstract Rhodococcus opacus PD630 was investigated for physiological and morphological changes under water stress challenge. Gluconate- and hexadecane-grown cells were extremely resistant to these conditions, and survival accounted for up to 300 and 400 days; respectively, when they were subjected to slow air-drying. Results of this study suggest that strain PD630 has specific mechanisms to withstand water stress. Water-stressed cells were sensitive to the application of ethanol, high temperatures and oxidative stress, whereas they exhibited cross-protection solely against osmotic stress during the first hours of application. Results indicate that the resistance programme for water stress in R. opacus PD630 includes the following physiological and morphological changes, among others: (1) energetic adjustments with drastic reduction of the metabolic activity (,39% decrease during the first 24 h and about 90% after 190 days under dehydration), (2) endogenous metabolism using intracellular triacylglycerols for generating energy and precursors, (3) biosynthesis of different osmolytes such as trehalose, ectoine and hydroxyectoine, which may achieve a water balance through osmotic adjustment and may explain the overlap between water and osmotic stress, (4) adjustments of the cell-wall through the turnover of mycolic acid species, as preliminary experiments revealed no evident changes in the thickness of the cell envelope, (5) formation of short fragmenting-cells as probable resistance forms, (6) production of an extracellular slime covering the surface of colonies, which probably regulates internal and external c anges in water potential, and (7) formation of compact masses of cells. This contributes to understanding the water stress resistance processes in the soil bacterium R. opacus PD630. [source] Physiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritimaAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Megdiche Wided Abstract Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco-physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance- and salt-dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose-dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na+ and Cl,, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt-challenged. Résumé Cakile maritima a été collecté (famille des Brassicaceae) dans trois provenances appartenant à des étages bioclimatiques différentes (humide, semi-aride et aride) de la Tunisie, dans le but d'étudier leurs réponses éco-physiologique et biochimique à la salinité. Des plantules ont été cultivées dans du sable inerte pendant vingt jours avec des doses croissantes de NaCl (0, 100, 200 et 400 mm NaCl). La réponse de Cakile maritima dépend de la provenance et de la salinité du milieu. A 100 mm de NaCl, les paramètres de croissance (biomasse, surface et nombre des feuilles par plante ainsi que le taux de la croissance relative) ont été améliorés chez Djerba (zone bioclimatique aride) par comparaison aux plantes témoins, tandis que la croissance a été réduite chez Tabarka (zone humide). A la plus forte dose de sel (400 mm), une réduction de la croissance des trois provenances a été enregistrée avec une nette sensibilité chez les plantes de la provenance Tabarka. La tolérance relative des deux provenances Djerba et Bekalta est associée à une faible teneur en malondialdéhyde ainsi qu'une fuite d'électrolyte et activité endo-protéolytique modérées. Le traitement salin a réduit l'hydratation des feuilles et cette diminution du contenu en eau est dose-dépendante et elle est plus prononcée chez Tabarka. En outre, l'augmentation de la salinité du milieu a entrainé une élévation de la succulence des feuilles concomitante à une diminution du potentiel hydrique notamment chez Djerba. Les plantes de cette dernière ont été les plus riches en Na+ et Cl - , en proline, carbohydrates, en protéines solubles et en polyphénols. En général, la tolérance au sel de la provenance Djerba, et à moindre degré Bekalta, est en partie reliée à la meilleure capacité d'ajustement osmotique et la limitation des dommages oxydatifs sous stress salin. [source] Plant responses to drought and phosphorus deficiency: contribution of phytohormones in root-related processesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2005Lutz Wittenmayer Abstract Environmental stresses are one of the most limiting factors in agricultural productivity. A large portion of the annual crop yield is lost to pathogens (biotic stress) or the detrimental effects of abiotic-stress conditions. There are numerous reports about chemical characterization of quantitatively significant substrate fluxes in plant responses to stress factors in the root-rhizosphere system, e.g., nutrient mobilization, heavy-metal and aluminum immobilization, or establishment of plant-growth-promoting rhizobacteria (PGPR) by exudation of organic anions, phytosiderophores, or carbohydrates into the soil, respectively. The hormonal regulation of these responses is not well understood. This paper highlights this complex process, stressing the involvement of phytohormones in plant responses to drought and phosphorus deficiency as examples. Beside ethylene, abscisic acid (ABA) plays an important role in drought-stress adaptation of plants. This hormone causes morphological and chemical changes in plants, ensuring plant survival under water-limited conditions. For example, ABA induces stomata closure, reduction in leaf surface, and increase in root : shoot ratio and, thus, reduction in transpiration and increase in soil volume for water uptake. Furthermore, it supports water uptake in soil with decreasing water potential by osmotic adjustment. Suitability of hormonal parameters in the selection for improving stress resistance is discussed. Auxins, ethylene, and cytokinins are involved in morphological adaption processes to phosphorus (P) deficiency (increase in root surface, e.g., by the formation of more dense root hairs or cluster roots). Furthermore, indole-3-acetic acid increases root exudation for direct and indirect phosphorus mobilization in soil. Nevertheless, the direct use of the trait "hormone content" of a particular plant organ or tissue, for example the use of the drought-stress-induced ABA content of detached leaves in plant breeding for drought-stress-resistant crops, seems to be questionable, because this procedure does not consider the systemic principle of hormonal regulation in plants. Reaktionen von Pflanzen auf Trockenstress und Phosphormangel: Die Rolle von Phytohormonen in wurzelbezogenen Prozessen Umweltstress stellt den wesentlichsten Limitierungsfaktor für die landwirtschaftliche Produktion dar. Ein erheblicher Teil der jährlichen Ernten geht durch pathogene Organismen (biotischer Stress) oder durch die verheerende Wirkung abiotischer Stressoren verloren (v. a. Trockenstress und Nährstoffmangel). Es gibt zahlreiche Untersuchungen zur stofflichen Charakterisierung der pflanzlichen Stressreaktion an der Wurzel, z.,B. Nährstoffmobilisierung, Schadstoffimmobilisierung oder Etablierung von wachstumsfördernden Rhizobakterien durch Wurzelabscheidungen. Die hormonelle Steuerung dieser Prozesse ist bisher weniger erforscht. Der Artikel geht dieser Problematik am Beispiel von Trockenstress und Phosphormangel unter besonderer Berücksichtigung von Phytohormonen nach. Bei der Anpassung von Pflanzen an Wassermangelbedingungen spielt neben Ethylen das Phytohormon Abscisinsäure (ABA) eine wichtige Rolle. Es induziert morphologische und chemische Veränderungen in der Pflanze, die ein Überleben unter Wassermangelbedingungen ermöglichen. Beispielsweise induziert die ABA den Stomataschluss, eine Verringerung der Blattoberfläche sowie eine Erhöhung des Wurzel:Spross-Verhältnisses und bewirkt dadurch eine verringerte Transpiration und Vergrößerung des Bodenvolumens zur Erschließung von Wasservorräten. Darüber hinaus kann eine ABA-induzierte Anreicherung von osmotisch wirksamen Verbindungen zur Wasseraufnahme bei sinkendem Wasserpotential im Boden beitragen. Bei Phosphat (P)-Mangel sind vor allem Auxine, Cytokine und Ethylen an der morphologischen Anpassung der Wurzeln (Vergrößerung der Wurzeloberfläche durch verstärkte Bildung von Wurzelhaaren oder Proteoidwurzeln) beteiligt. Darüber hinaus bewirkt Indolyl-3-Essigäure eine Intensivierung der Abgabe von Wurzelabscheidungen zur direkten oder indirekten P-Mobilisierung in der Rhizosphäre. Trotzdem wird die unmittelbare Verwendung des Indikators "Hormongehalt" eines bestimmten Pflanzenorganes, beispielsweise der trockenstressinduzierte ABA-Gehalt von abgeschnittenen Blättern, für die Züchtung auf Stressresistenz als problematisch angesehen, da sie das systemische Prinzip der Hormonregulation nicht berücksichtigt. [source] Foliar dehydration tolerance of mycorrhizal cowpea, soybean and bush beanNEW PHYTOLOGIST, Issue 2 2001Robert M. Augé Summary ,,Foliar dehydration tolerance of three mycorrhizal and nonmycorrhizal legumes is presented here. ,,Leaf water potential, osmotic adjustment and soil matric potential at the end of a lethal drying episode were compared in soybean, cowpea and bush bean colonized or uncolonized by Glomus intraradices. ,,Lethal leaf water potential were similar among treatments except in soybean, for which nonmycorrhizal plants given low phosphorus fertilization had values 0.3,0.4 MPa lower than mycorrhizal plants or nonmycorrhizal plants given higher phosphorus fertilization. Mycorrhizal symbiosis did not affect osmotic adjustment or lethal soil matric potential. Nonmycorrhizal cowpeas given low phosphorus showed more osmotic adjustment than nonmycorrhizal cowpeas given higher phosphorus. Foliage of host species typically classified as drought avoiders, cowpea and bush bean, survived to lower soil matric potentials than soybean, although soybean foliage was more tolerant of dehydration. ,,Our findings support the idea that when arbuscular mycorrhizal plants fare better than nonmycorrhizal plants during drought, it is probably due to enhanced drought avoidance capabilities conferred by the symbiosis rather than to changes in ability of foliage to withstand dehydration. [source] Biochemical and molecular responses to water stress in resurrection plantsPHYSIOLOGIA PLANTARUM, Issue 2 2004Giovanni Bernacchia A small group of angiosperms, known as resurrection plants, can tolerate extreme dehydration. They survive in arid environments because they are able to dehydrate, remain quiescent during long periods of drought, and then resurrect upon rehydration. Dehydration induces the expression of a large number of transcripts in resurrection plants. Gene products with a putative protective function such as LEA proteins have been identified; they are expressed at high levels in the cytoplasm or in chloroplasts upon dehydration and/or ABA treatment of vegetative tissue. An increase in sugar concentration is usually observed at the onset of desiccation in vegetative tissue of resurrection plants. These sugars may be effective in osmotic adjustment or they may stabilize membrane structures and proteins. Regulatory genes such as a protein translation initiation factor, homeodomain-leucine zipper genes and a gene probably working as a regulatory RNA have been isolated and characterized. The knowledge of the biochemical and molecular responses that occur during the onset of drought may help to improve water stress tolerance in plants of agronomic importance. [source] Water relations and gas exchange in poplar and willow under water stress and elevated atmospheric CO2PHYSIOLOGIA PLANTARUM, Issue 1 2002Jon D. Johnson Predictions of shifts in rainfall patterns as atmospheric [CO2] increases could impact the growth of fast growing trees such as Populus spp. and Salix spp. and the interaction between elevated CO2 and water stress in these species is unknown. The objectives of this study were to characterize the responses to elevated CO2 and water stress in these two species, and to determine if elevated CO2 mitigated drought stress effects. Gas exchange, water potential components, whole plant transpiration and growth response to soil drying and recovery were assessed in hybrid poplar (clone 53,246) and willow (Salix sagitta) rooted cuttings growing in either ambient (350 µmol mol,1) or elevated (700 µmol mol,1) atmospheric CO2 concentration ([CO2]). Predawn water potential decreased with increasing water stress while midday water potentials remained unchanged (isohydric response). Turgor potentials at both predawn and midday increased in elevated [CO2], indicative of osmotic adjustment. Gas exchange was reduced by water stress while elevated [CO2] increased photosynthetic rates, reduced leaf conductance and nearly doubled instantaneous transpiration efficiency in both species. Dark respiration decreased in elevated [CO2] and water stress reduced Rd in the trees growing in ambient [CO2]. Willow had 56% lower whole plant hydraulic conductivity than poplar, and showed a 14% increase in elevated [CO2] while poplar was unresponsive. The physiological responses exhibited by poplar and willow to elevated [CO2] and water stress, singly, suggest that these species respond like other tree species. The interaction of [CO2] and water stress suggests that elevated [CO2] did mitigate the effects of water stress in willow, but not in poplar. [source] Differences in efficient metabolite management and nutrient metabolic regulation between wild and cultivated barley grown at high salinityPLANT BIOLOGY, Issue 4 2010Sabah Yousfi Abstract Physiological and biochemical responses of Hordeum maritimum and H. vulgare to salt stress were studied over a 60-h period. Growth at increasing salinity levels (0, 100, 200 and 300 mM NaCl) was assessed in hydroponic culture. H. maritimum was shown to be a true halophyte via its typical behaviour at high salinity. Shoot growth of cultivated barley was gradually reduced with increasing salinity, whereas that of wild barley was enhanced at 100 and 200 mm NaCl then slightly reduced at 300 mM NaCl. The higher salt tolerance of H. maritimum as compared to H. vulgare was due to its higher capacity to maintain cell turgor under severe salinity. Furthermore, H. maritimum exhibited fine regulation of Na+ transport from roots to shoots and, unlike H. vulgare, it accumulated less Na+ in shoots than in roots. In addition, H. maritimum can accumulate more Na+ than K+ in both roots and shoots without the appearance of toxicity symptoms, indicating that Na+ was well compartmentalized within cells and substituted K+ in osmotic adjustment. The higher degree of salt tolerance of H. maritimum is further demonstrated by its economic strategy: at moderate salt treatment (100 mm NaCl), it used inorganic solutes (such as Na+) for osmotic adjustment and kept organic solutes and a large part of the K+ for metabolic activities. Indeed, K+ use efficiency in H. maritimum was about twofold that in H. vulgare; the former started to use organic solutes as osmotica only at high salinity (200 and 300 mm NaCl). These results suggest that the differences in salt tolerance between H. maritimum and H. vulgare are partly due to (i) differences in control of Na+ transport from roots to shoots, and (ii) H. maritimum uses Na+ as an osmoticum instead of K+ and organic solutes. These factors are differently reflected in growth. [source] Solute Heterogeneity and Osmotic Adjustment in Different Leaf Structures of Semi-Leafless Pea (Pisum sativum L.) Subjected to Water StressPLANT BIOLOGY, Issue 5 2002E. M. González Abstract: Semi-leafless varieties of pea have considerable agronomic importance and it has been suggested that they may have a superior response to water deficits than conventional varieties. However, these varieties are poorly characterized from a physiological point of view and there is lack of a physiological basis for their supposed better performance under conditions of water deficit. Here, we describe the solute distribution in the different leaf structures of a semi-leafless pea variety (Pisum sativum L.) under non-limiting water conditions and under water stress. A conventional variety was subjected to the same conditions for comparative purposes. A detailed study was carried out both at the tissue level and at the single cell level. In control conditions, epidermal vacuoles of tendrils showed a different ion distribution of those of the laminar leaf structures. However, under water deficit, only stipules of the semi-leafless variety showed a significantly higher capability to increase osmolarity. This occurred by accumulating potassium, magnesium and chloride to a higher extent than other leaf structures. The inability of performing an adequate osmotic adjustment in tendrils may be the cause of the lack of a better response to water deficit. [source] Quercitol and osmotic adaptation of field-grown Eucalyptus under seasonal drought stressPLANT CELL & ENVIRONMENT, Issue 7 2008STEFAN K. ARNDT ABSTRACT This study investigated the role of quercitol in osmotic adjustment in field-grown Eucalyptus astringens Maiden subject to seasonal drought stress over the course of 1 year. The trees grew in a native woodland and a farm plantation in the semi-arid wheatbelt region of south Western Australia. Plantation trees allocated relatively more biomass to leaves than woodland trees, but they suffered greater drought stress over summer, as indicated by lower water potentials, CO2 assimilation rates and stomatal conductances. In contrast, woodland trees had relatively fewer leaves and suffered less drought stress. Plantation trees under drought stress engaged in osmotic adjustment, but woodland trees did not. Quercitol made a significant contribution to osmotic adjustment in drought-stressed trees (25% of total solutes), and substantially more quercitol was measured in the leaves of plantation trees (5% dry matter) than in the leaves of woodland trees (2% dry matter). We found no evidence that quercitol was used as a carbon storage compound while starch reserves were depleted under drought stress. Differences in stomatal conductance, biomass allocation and quercitol production clearly indicate that E. astringens is both morphologically and physiologically ,plastic' in response to growth environment, and that osmotic adjustment is only one part of a complex strategy employed by this species to tolerate drought. [source] NMR metabolite profiling analysis reveals changes in phospholipid metabolism associated with the re-establishment of desiccation tolerance upon osmotic stress in germinated radicles of cucumberPLANT CELL & ENVIRONMENT, Issue 4 2006M.-H. AVELANGE-MACHEREL ABSTRACT The adaptation of metabolism is thought to play a role in the acquisition of desiccation tolerance (DT). However, the importance of such a role and whether specific regulatory pathways exist remain to be assessed. Using in vitro31P and 13C nuclear magnetic resonance (NMR) spectroscopy and biochemical assays, we analysed metabolite profiles of perchloric extracts from germinating radicles of cucumber to identify changes in carbon and phosphate metabolism associated with DT. Emerged radicles measuring 2 mm long can be rendered tolerant to desiccation by incubation in a polyethylene glycol (PEG) solution with a water potential of ,1.5 MPa. However, in 4-mm-long emerged radicles, this treatment was ineffective. This manipulable system enabled the discrimination of changes in metabolites associated with DT from those associated with the response to osmotic stress. Independent of radicle length, the PEG treatment resulted in an increase in sucrose (Suc) content, whereas glucose (Glc), fructose (Fru) and the hexose phosphate pool, as well as phosphoenolpyruvate decreased three- to fourfold. In addition, three derivatives arising early during phospholipid catabolism (glycerylphosphorylcholine, glycerylphosphorylethanolamine and glycerylphosphorylinositol) appeared in the PEG-treated radicles. Interestingly, phospholipid degradation was much more pronounced in osmotically challenged radicles that remain sensitive to drying. This was proved by the appearance of catabolites, such as phosphocholine and phosphoethanolamine, solely in 4 mm PEG-treated radicles. Furthermore, glycerol-3-phosphate and its derivative 3-phosphoglycerate increased significantly. Our data suggest that the metabolic response leading to the re-establishment of DT is not entirely identical to that of an osmotic response. It is inferred that membrane remodelling and/or increased phospholipid catabolism is an adaptive response common to osmotic adjustment and DT but is controlled differently in tolerant and sensitive radicles. [source] Nickel and zinc hyperaccumulation by Alyssum murale and Thlaspi caerulescens (Brassicaceae) do not enhance survival and whole-plant growth under drought stressPLANT CELL & ENVIRONMENT, Issue 3 2003S. N. WHITING ABSTRACT Nickel and Zn hyperaccumulation by Alyssum murale and Thlaspi caerulescens bear substantial energetic costs and should confer benefits to the plant. This research determined whether metal hyperaccumulation can increase osmotic adjustment and resistance to water stress (drought). Alyssum murale and Thlaspi caerulescens treated with low or high concentrations of Ni or Zn were exposed to moderate (,0·4 MPa) and severe (,1·0 MPa) water stresses using aqueous polyethylene glycol. In the absence of metals both water deficits inhibited shoot growth. Nickel and Zn hyperaccumulation did not ameliorate growth inhibition by either level of water stress. The water stress did not induce major changes in shoot metal concentrations of these constitutive hyperaccumulators. Moreover, metal hyperaccumulation had minimal effects on the osmolality of leaf-sap extracts, relative water content of the shoots, or rate of evapotranspiration. It is concluded that Ni or Zn hyperaccumulation does not augment whole-plant capacity for drought resistance in A. murale and T. caerulescens. [source] Physiological responses of lupin genotypes to terminal drought in a Mediterranean-type environmentANNALS OF APPLIED BIOLOGY, Issue 3 2007J.A. Palta Abstract Field experiments concerning lupin grown in a low-rainfall environment of the Mediterranean climatic region of Western Australia were conducted over three seasons to identify and evaluate the characteristics that maximise yield per unit of rainfall. The characteristics of early flowering and podding, high pod retention, fast rates of seed filling, osmotic adjustment and the degree of dry matter transfer from stem to the seed were studied in 12 lupin genotypes differing in seed yield under conditions of terminal drought. To allow recently released cultivars and advanced breeding lines to be evaluated, five to six genotypes were included in the first and the third year and nine in the second year. The genotypes were grown rainfed until pod set and then under a rainout shelter. Flowering and podding dates, pod retention, seed growth rate and osmotic adjustment were measured in detail, together with leaf water potential, seed yield and its components. The timing and intensity of development of the terminal drought varied from average in 1998 and 1999 to extreme in 2000. In each year, the seed yield under terminal drought showed genotypic differences, which appeared consistent with the timing and intensity of the development of terminal drought. Early flowering and podding were significantly correlated with seed yield. Fast rates of seed growth were highly and significantly correlated with high yields regardless of the intensity of development of terminal drought. Pod retention was highly correlated with yield in seasons in which the intensity of the development of terminal drought was average but not under extreme conditions of terminal drought. This was because the seed number per pod was markedly reduced to compensate for the high number of pods retained. Osmotic adjustment did not occur during the development of terminal drought in any of the genotypes. Dry matter transfer from stems to seeds was insignificant and not related to seed yield, suggesting that it is not a useful characteristic in screening for high yield under terminal drought. [source] Osmotic adjustment of chickpea (Cicer arietinum) is not associated with changes in carbohydrate composition or leaf gas exchange under droughtANNALS OF APPLIED BIOLOGY, Issue 2 2007P.S. Basu Abstract Genetic differences in osmotic adjustment (OA) have been reported among chickpea (Cicer arietinum) cultivars. In this study eight advanced breeding lines (ABLs) derived from a cross between CTS 60543 (high OA) and Kaniva (low OA) and Tyson (medium OA) and Kaniva, along with the parents, were evaluated for OA, leaf carbohydrate composition and leaf gas exchange under dryland field conditions in India. The water potential (WP) decreased to lower values (less than ,2.5 MPa) in Tyson, M 110 and M 86 than in the other genotypes. With decrease in WP, OA increased by 0.5 MPa in Kaniva and CTS 60543 to 1.3 MPa in M 55. As the decrease in WP varied with genotype, when OA was regressed against WP M 39 and M 55 had greater increases in OA with decrease in WP than the remaining nine genotypes, including the parents. As WP decreased, leaf starch content decreased while total soluble sugars, hexoses and sucrose increased: the decrease in starch was much smaller in M 93 and M 129 than in Tyson and M 51, but genotypic differences could not be detected in the increase in total sugars, hexoses or sucrose. The rates of photosynthesis and transpiration decreased as the WP became more negative, but M 129 reached low rates of photosynthesis (2 ,mol m,2 s,1) and transpiration at a WP of ,1.7 MPa, whereas Tyson reached the same low rate at ,2.4 MPa. While OA varied among the chickpea genotypes, the differences were not associated with the changes in carbohydrate composition or the rates of gas exchange at low values of WP. Further, the degree of OA of the 11 genotypes was not the same as when they were selected for differences in OA under rainout shelter conditions in the field in Australia, suggesting that OA may show poor stability depending upon the stress level, location or physiological stage of the plant. This suggests that OA is not a valuable drought-resistance trait to select for in chickpea breeding programmes. [source] Sustainable production of crops and pastures under drought in a Mediterranean environmentANNALS OF APPLIED BIOLOGY, Issue 2 2004NEIL C TURNER Summary Mediterranean environments are characterised by cool wet winters and hot dry summers. While native vegetation in Mediterranean-climatic zones usually comprises a mixture of perennial and annual plants, agricultural development in the Mediterranean-climatic region of Australia has led to the clearing of the perennial vegetation and its replacement with annual crops and pastures. In the Mediterranean environments of southern Australia this has led to secondary (dryland) salinisation. In order to slow land degradation, perennial trees and pasture species are being reintroduced to increase the productivity of the saline areas. The annual crops and pastures that form the backbone of dryland farming systems in the Mediterranean-climatic zone of Australia are grown during the cool wet winter months on incoming rainfall and mature during spring and early summer as temperatures and rates of evaporation rise and rainfall decreases. Thus, crop and pasture growth is usually curtailed by terminal drought. Where available, supplementary irrigation in spring can lead to significant increases in yield and water use efficiency. In order to sustain production of annual crops in Mediterranean environments, both agronomic and genetic options have been employed. An analysis of the yield increases of wheat in Mediterranean-climatic regions shows that there has generally been an increase in the yields over the past decades, albeit at a lower rate than in more temperate regions. Approximately half of this increase can be attributed to agronomic improvements and half to genetic improvements. The agronomic improvements that have been utilised to sustain the increased yields include earlier planting to more closely match crop growth to rainfall distribution, use of fertilisers to increase early growth, minimum tillage to enable earlier planting and increase plant transpiration at the expense of soil evaporation, rotations to reduce weed control and disease incidence, and use of herbicides, insecticides and fungicides to reduce losses from weeds, insects and disease. Genetic improvements include changing the phenological development to better match the rainfall, increased early vigour, deeper rooting, osmotic adjustment, increased transpiration efficiency and improved assimilate storage and remobilisation. Mediterranean environments that are subjected annually to terminal drought can be both environmentally and economically sustainable, but to maximise plant water use efficiency while maintaining crop productivity requires an understanding of the interaction between genotypes, environment and management. [source] Use of stomatal conductance and pre-dawn water potential to classify terroir for the grape variety KékfrankosAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 1 2009Zs. ZSÓFI Abstract Background and Aims:, A 3-year study was carried out in order to evaluate the ecophysiology, yield and quality characteristics of Vitis vinifera L. cv. Kékfrankos (syn. Limberger) at Eger-Nagyeged hill (steep slope) and at Eger-K,lyuktet, (flat) vineyard sites located in the Eger wine region, Hungary. The aim of this paper was to analyse the effect of ,vintage' and ,terroir' on the seasonal changes of Kékfrankos ecophysiology and its possible relationship with yield and wine composition. Methods and Results:, Grapevine physiological responses (midday- and pre-dawn water potential, pressure,volume analysis and gas-exchange), growing stages, yield and wine composition of each vineyard were studied. Lower grapevine water supply was detected at Eger-Nagyeged hill in each season due to its steep slope and soil characteristics. Pressure-volume curves indicated that there was no osmotic adjustment in the leaves of this variety. Higher osmotic concentration was measured at turgor loss and full turgor in the leaves of the unstressed vineyard (Eger-K,lyuktet,) presumably due to higher photosynthetic activity. Differences in soil water content of the vineyards resulted in a slightly altered cell wall elasticity. Stomatal conductance, transpiration rate and photosynthetic production per unit leaf area were affected by water availability. Lower yield in Eger-Nagyeged hill was partly associated with decreased photosynthetic production of the canopy. Improved wine quality of Eger-Nagyeged hill was due to moderate water stress which induced higher concentration of anthocyanins and phenolics in the berries. The duration of the phenological stages was dependent on vintage temperature characteristics rather than on vineyard site. Conclusion:, There was a close relationship between environmental conditions, Kékfrankos gas-exchange, water relations, yield and wine composition. Water deficit plays an important role in creating a terroir effect, resulting in decreased yield, better sun exposure of leaves and clusters and thus higher concentration of phenolics and anthocyanins. Although quality is mainly influenced by vintage differences, vineyard characteristics are able to buffer unfavourable vintage effects even within a small wine region. Significance of the Study:, Stomatal conductance, pre-dawn water potential and climatic data may be reliable parameters for terroir classification, although variety,terroir interactions must always be considered. [source] Effect Of Height On Tree Hydraulic Conductance Incompletely Compensated By Xylem TaperingFUNCTIONAL ECOLOGY, Issue 2 2005S. ZAEHLE Summary 1The hydraulic limitation theory proposes that the decline of forest productivity with age is a consequence of the loss of whole-plant and leaf-specific hydraulic conductance with tree height caused by increased friction. Recent theoretical analyses have suggested that tapering (the broadening of xylem vessel diameter from terminal branches to the base of the stem) could compensate completely for the effect of tree height on hydraulic conductance, and thus on tree growth. 2The data available for testing this hypothesis are limited, but they do not support the implication that whole-tree and leaf-specific hydraulic conductance are generally independent of tree height. Tapering cannot exclude hydraulic limitation as the principle mechanism for the observed decline in growth. 3Reduction of the leaf-to-sapwood area ratio, decreased leaf water potential, loss of leaf-cell turgor, or osmotic adjustments in taller trees could reduce the effect of increased plant hydraulic resistance on stomatal conductance with height. However, these mechanisms operate with diminishing returns, as they infer increased costs to the tree that will ultimately limit tree growth. To understand the decline in forest growth, the effects of these acclimation mechanisms on carbon uptake and allocation should be considered. [source] Assimilate transport in grapevines -effect of phloem disruptionAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 3 2001J.J.(KOBUS) HUNTER Abstract Assimilate translocation in mature grapevines (cv. Gewürztraminer and cv. Harslevelü) under field conditions was investigated during the growth season by quantifying individual sugars and organic acids in mature leaves, shoot bark and berries, as affected by girdling the shoot just above the bunches. Tissue was sampled at berry set, pea size, veraison and ripeness stages of the vine. Invertase activity was determined in the shoot bark at ripeness. In the leaves, malic acid concentrations reached lowest levels at pea size, but increased thereafter. Tartaric acid decreased after peaking at pea size stage. Tartaric acid concentrations increased with girdling. Despite the increase in leaf age, sucrose concentrations remained virtually stable during the season, emphasising the importance of mature leaves for nourishing bunches. Girdling resulted in a build-up of sucrose in the leaves. In the bark, malic and tartaric acid stayed more or less the same during the growth period, but increased above the girdle. As a result of phloem disruption, sucrose also increased. The increase in glucose and tartaric acid is believed to result from catabolic cleavage of sucrose by invertase. Invertase activity was evident in the bark (of mature Harslevelü vines) at ripeness, which may indicate involvement in osmotic adjustments and gradients in the bark/phloem structure. In the berries, malic and tartaric acids reached peak concentrations at pea size. The volume increase during the ripening period, and in the case of malic acid also respiratory loss, resulted in a decrease in organic acid concentration. Malic acid continued to decrease after the initial decline, whereas tartaric acid stayed virtually stable. Girdling had no marked effect on organic acid accumulation in the berries. Sucrose concentrations were low during the first part of the season, but increased thereafter. Sucrose concentrations during ripening increased with girdling, which may represent a concentration effect and/or import from the rest of the vine. Sucrose concentrations (in mature Harslevelü vines) were indeed lower below than above the girdle. Comparison of sucrose concentrations in the leaves, bark and berries showed the existence of a decreasing concentration gradient, in line with the source:sink transport concept. An equally prominent decrease in sucrose:glucose ratio in the berries from the start of the ripening period indicates that vacuolar integrity (compartmentation) was affected in the ripening berry, most probably allowing hydrolysis of sucrose by invertase and decreasing osmotic potential within the berry. The results provide further evidence for the hypothesis of an osmotic gradient driven transport to the berry. [source] | |||||||||||||||||||||||||