Physiologia Plantarum
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Contribution of six arbuscular mycorrhizal fungal isolates to water uptake by <i>Lactuca sativa</i> plants under drought stress It is currently accepted that, along with nutrients, arbuscular mycorrhizal (AM) fungi also transport water to their host plant. However, the quantity of water supplied and its significance for plant water relations remain controversial. The objective of this work was to evaluate and compare the ability of six AM fungi to alter rates of root water uptake under drought stress conditions. Soil drying rates of uninoculated control plants of comparable size and nutritional status and mycorrhizal plants were recorded daily. Lactuca sativa plants colonized by Glomus coronatum , G. intraradices , G. claroideum and G. mosseae depleted soil water to a higher extent than comparably sized uninoculated control plants or plants colonized by G. constrictum or G. geosporum . The differences ranged from 0.6% volumetric soil moisture for G. mosseae ‐colonized plants to 0.95% volumetric soil moisture for G. intraradices ‐colonized plants. These differences in soil moisture were equivalent to 3–4.75 ml plant−1 day−1 , respectively, and could not be ascribed to differences in plant size, but to the activity of AM fungi. The AM fungi tested in this study differed in their effectiveness to enhance plant water uptake from soil. This ability seems to be related to the amount of external mycelium produced by each AM fungus and to the frequency of root colonization in terms of live and active fungal structures.
Physiologia Plantarum - Tập 119 Số 4 - Trang 526-533 - 2003
Effect of arbuscular mycorrhizal inoculation on water status and photosynthesis of <i>Populus cathayana</i> males and females under water stress Drought is one of the most serious environmental limitations for poplar growth. Although the ways in which plants deal with water stress and the effects of arbuscular mycorrhizal (AM ) formation have been well documented, little is known about how the male and female plants of Populus cathayana respond to drought and AM formation. We also aimed to investigate the potential role of AM fungi in maintaining gender balance. We tested the impact of drought and AM formation on water status and photosynthesis. The results suggested that both sexes showed similar responses to water stress: drought decreased the growth of stem length (GSL ), growth of ground diameter (GGD ), relative water content (RWC ), increased the relative electrolyte leakage (REL ), and limited the photosynthesis and chlorophyll fluorescence indexes. However, the responses of the two sexes to drought and AM formation differed to some extent. AM formation had positive effects on RWC , photosynthesis and the intrinsic water use efficiency (WUEi ) but negative effects on the REL of males and females, especially under drought. AM formation enhanced the maximum quantum yield of photosystem II (PSII) (Fv/Fm), the actual quantum yield of PSII (ΦPSII ), non‐photochemical quenching (qN ) and photochemical quenching (qP ) under drought conditions, and had no significant effects under well‐watered conditions except on the qP of males. Principal component analysis showed that males were significantly more drought tolerant than females, and AM formation enhanced drought tolerance, particularly among males, which suggested that AM fungi are beneficial for ecological stability and for P . cathayana survival under drought conditions.
Physiologia Plantarum - Tập 155 Số 2 - Trang 192-204 - 2015
Hyphal contribution to water uptake in mycorrhizal plants as affected by the fungal species and water status Vesicular‐arbuscular mycorrhizae may increase resistance of plants to drought by a number of mechanisms, such as increased root hydraulic conductivity, stomatal regulation, hyphal water uptake and osmotic adjustment. However, a substantial contribution of vesicular‐arbuscular mycorrhizal (VAM) hyphae to water uptake has not been demonstrated unequivocally. The objective of this investigation was to examine the contribution of hyphae from two VAM fungi to water uptake and transport by the host plant. Lettuce (Lactuca sativa L.) plants were grown in a container divided by a screen into two compartments. One was occupied by roots, the other only by VAM hyphae, which the screen permitted to pass. Roots were colonized by the VAM fungi Glomus deserticola or Glomus fasciculatum , or were left uninoculated but P‐supplemented. Water was supplied to the hyphal compartment at a distance of 10 cm from the screen (root). CO2 exchange rate, water‐use efficiency, transpiration, stomatal conductance and photosynthetic phosphorus‐use efficiency of VAM or P‐amended control plants were evaluated at three levels of water application in the hyphal compartment. Results indicate that much of the water was taken up by the hyphae in VAM plants. VAM plants, which had access to the hyphal compartment, had higher water and nutrient contents. G. deserticola functioned efficiently under water limitation and mycelium from G. fasciculatum ‐colonized plants was very sensitive to water in the medium. This discrepancy in VAM behaviour reflects the various abilities of each fungus according to soil water levels. Different abilities of specific mycelia were also expressed in terms of nutritional and leaf gas‐exchange parameters. G. fasciculatum caused a significant increase in net photosynthesis and rate of water use efficiency compared to G. deserticola and P‐fertilized plants. In contrast, the G. deserticola treatment was the most efficient affecting N, P and K nutrition, leaf conductance and transpiration. Since no differences in the intra‐ and extra‐radical hyphal extension of the two endophytes were found, the results demonstrate that mycorrhizal hyphae can take up water and that there are considerable variations in both the behaviour of these two VAM fungi and in the mechanisms involved in their effects on plant water relations.
Physiologia Plantarum - Tập 95 Số 3 - Trang 472-478 - 1995
Sulfate deficiency stimulates release of dissolved organic matter in synchronous cultures of Scenedesmus obliquus In synchronous cultures of the green alga Scenedesmus 276–3a suboptmal sulfate supply increases the concentration of dissolved organics considerably. The highest level of extracellular organic substances occurs at sulfate dosages which reduce growth by 50‐70% as compared to control cultures growing under standard conditions. Sulfate deficiency causes increased synthesis of carbohydrate and reduces the production of crude protein and chlorophyll almost simultaneously at incipient sulfur deficiency. Since the concentration of extracellular organic substance rises at the same time, this symptom of partial sulfur deficiency is interpreted as resulting from an imbalance between the production and utilization of photosynthetic products. Part of the excess carbohydrate is retained in the cells.
Physiologia Plantarum - Tập 52 Số 2 - Trang 233-238 - 1981
Comparative analysis of gene expression under cold acclimation, deacclimation and reacclimation in Arabidopsis Cold acclimated plants show an elevated tolerance against subsequent cold stress. Such adaptation requires alterations in gene expression as well as physiological changes. We were interested in gene expression changes at the transcriptional level during adaptation processes. The patterns of transcriptional changes associated with cold acclimation, deacclimation and reacclimation in Arabidopsis leaves were characterized using the Coldstresschip. Gene expression profiles were further analyzed by ‘coexpressed gene sets’ using gene set enrichment analysis (GSEA ). Genes involved in signal transduction through calcium, and cascades of kinases and transcription factor genes, were distinctively induced in the early response of cold acclimation. On the other hand, genes involved in antioxidation, cell wall biogenesis and sterol synthesis were upregulated in the late response of cold acclimation. After the removal of cold, the expression patterns of most genes rapidly returned to the original states. However, photosynthetic light‐harvesting complex genes and lipid metabolism‐related genes stayed upregulated in cold deacclimated plants compared to non‐treated plants. It is also notable that many well‐known cold‐inducible genes are slightly induced in reacclimation and their expression remains at relatively low levels in cold reacclimation compared to the expression during the first cold acclimation. The results in this study show the dynamic nature of gene expression occurring during cold acclimation, deacclimation and reacclimation. Our results suggest that there is a memory of cold stress and that the ‘memory of cold stress’ is possibly due to elevated photosynthetic efficiency, modified lipid metabolism, increased calcium signaling, pre‐existing defense protein made during first cold acclimation and/or modified signal transduction from pre‐existing defense protein.
Physiologia Plantarum - Tập 152 Số 2 - Trang 256-274 - 2014
Correlation between hormonal homeostasis and morphogenic responses in <i>Arabidopsis thaliana</i> seedlings growing in a Cd/Cu/Zn multi‐pollution context To date, almost no information is available in roots and shoots of the model plant Arabidopsis thaliana about the hierarchic relationship between metal accumulation, phytohormone levels, and glutathione/phytochelatin content, and how this relation affects root development. For this purpose, specific concentrations of cadmium, copper and zinc, alone or in triple combination, were supplied for 12 days to in vitro growing seedlings. The accumulation of these metals was measured in roots and shoots, and a significant competition in metal uptake was observed. Microscopic analyses revealed that root morphology was affected by metal exposure, and that the levels of trans ‐zeatin riboside, dihydrozeatin riboside, indole‐3‐acetic acid and the auxin/cytokinin ratio varied accordingly. By contrast, under metal treatments, minor modifications in gibberellic acid and abscisic acid levels occurred. Real‐time polymerase chain reaction analysis of some genes involved in auxin and cytokinin synthesis (e.g. AtNIT AtIPT AtGSH1 AtGSH2 AtPCS1 AtPCS2
Physiologia Plantarum - Tập 149 Số 4 - Trang 487-498 - 2013
Regulation of redox homeostasis in the yeast <i>Saccharomyces cerevisiae</i> An increasingly important area of research is based on sulphydryl chemistry, since the oxidation of ‐SH groups is one of the earliest observable events during oxidant‐mediated damage and ‐SH groups play a critical role in the function of many macromolecular structures including enzymes, transcription factors and membrane proteins. Glutaredoxins and thioredoxins are small heat‐stable oxidoreductases, conserved throughout evolution, which play key roles in maintaining the cellular redox balance. Much progress has been made in analysing these systems in the yeast Saccharomyces cerevisiae which is a very useful model eukaryote due to its ease of genetic manipulation, its compact genome, the availability of the entire genome sequence, and the current rate of progress in gene function research. Yeast, like all eukaryotes, contains a number of glutaredoxin and thioredoxin isoenzymes located in both the cytoplasm and the mitochondria. This review describes recent findings made in yeast that are leading to a better understanding of the regulation and role of redox homeostasis in eukaryotic cell metabolism.
Physiologia Plantarum - Tập 120 Số 1 - Trang 12-20 - 2004
Regulators of Cell Division in Plant Tissues XII. A Cytokinin Bioassay Using Excised Radish Cotyledons Abstract A rapid bioassay for cytokinins is described. This is based on the ability of these compounds to promote markedly the expansion of radish cotyledons excised soon after seed germination. The response, which is due largely to a promotion of cell enlargement, is inhibited by abscisic acid. Gibberellins, certain amino acids and calcium salts, naturally occurring substances without cytokinin activity, induce small growth increments in the assay. Cytokinin structure‐activity relationships observed for the assay are very similar to those which apply in the tobacco‐pith tissue culture assay.
Physiologia Plantarum - Tập 25 Số 3 - Trang 391-396 - 1971
Scanning ion‐selective electrode technique and X‐ray microanalysis provide direct evidence of contrasting Na<sup>+</sup> transport ability from root to shoot in salt‐sensitive cucumber and salt‐tolerant pumpkin under <scp>NaCl</scp> stress Grafting onto salt‐tolerant pumpkin rootstock can increase cucumber salt tolerance. Previous studies have suggested that this can be attributed to pumpkin roots with higher capacity to limit the transport of Na+ to the shoot than cucumber roots. However, the mechanism remains unclear. This study investigated the transport of Na+ in salt‐tolerant pumpkin and salt‐sensitive cucumber plants under high (200 mM ) or moderate (90 mM ) NaCl stress. Scanning ion‐selective electrode technique showed that pumpkin roots exhibited a higher capacity to extrude Na+ , and a correspondingly increased H+ influx under 200 or 90 mM NaCl stress. The 200 mM NaCl induced Na+ /H+ exchange in the root was inhibited by amiloride (a Na+ /H+ antiporter inhibitor) or vanadate [a plasma membrane (PM) H+ ‐ATPase inhibitor], indicating that Na+ exclusion in salt stressed pumpkin and cucumber roots was the result of an active Na+ /H+ antiporter across the PM, and the Na+ /H+ antiporter system in salt stressed pumpkin roots was sufficient to exclude Na+ . X‐ray microanalysis showed higher Na+ in the cortex, but lower Na+ in the stele of pumpkin roots than that in cucumber roots under 90 mM NaCl stress, suggesting that the highly vacuolated root cortical cells of pumpkin roots could sequester more Na+ , limit the radial transport of Na+ to the stele and thus restrict the transport of Na+ to the shoot. These results provide direct evidence for pumpkin roots with higher capacity to limit the transport of Na+ to the shoot than cucumber roots.
Physiologia Plantarum - Tập 152 Số 4 - Trang 738-748 - 2014
γ‐Aminobutyric acid addition alleviates ammonium toxicity by limiting ammonium accumulation in rice (<i>Oryza sativa</i>) seedlings Excessive use of nitrogen (N) fertilizer has increased ammonium (NH4 + ) accumulation in many paddy soils to levels that reduce rice vegetative biomass and yield. Based on studies of NH4 + toxicity in rice (Oryza sativa , Nanjing 44) seedlings cultured in agar medium, we found that NH4 + concentrations above 0.75 mM inhibited the growth of rice and caused NH4 + accumulation in both shoots and roots. Use of excessive NH4 + also induced rhizosphere acidification and inhibited the absorption of K, Ca, Mg, Fe and Zn in rice seedlings. Under excessive NH4 + conditions, exogenous γ‐aminobutyric acid (GABA) treatment limited NH4 + accumulation in rice seedlings, reduced NH4 + toxicity symptoms and promoted plant growth. GABA addition also reduced rhizosphere acidification and alleviated the inhibition of Ca, Mg, Fe and Zn absorption caused by excessive NH4 + . Furthermore, we found that the activity of glutamine synthetase/NADH‐glutamate synthase (GS; EC 6.3.1.2/NADH‐GOGAT; EC1.4.1.14) in root increased gradually as the NH4 + concentration increased. However, when the concentration of NH4 + is more than 3 mM , GABA treatment inhibited NH4 + ‐induced increases in GS/NADH‐GOGAT activity. The inhibition of ammonium assimilation may restore the elongation of seminal rice roots repressed by high NH4 + . These results suggest that mitigation of ammonium accumulation and assimilation is essential for GABA‐dependent alleviation of ammonium toxicity in rice seedlings.
Physiologia Plantarum - Tập 158 Số 4 - Trang 389-401 - 2016
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