Responses of pomegranate cultivars to severe water stress and recovery: changes on antioxidant enzyme activities,gene expression patterns and water stress responsive metabolites

The biochemical and molecular responses of five commercially well-known pomegranate cultivars to severe water stress were studied. The cultivars were subjected to 14-day water stress by withholding irrigation, followed by re-watering for 7 days. Results showed clear differences in metabolites contents and activities of antioxidant enzymes among various pomegranate cultivars during severe water stress and recovery. According to our results, increased accumulation of proline in pomegranate was not related to osmotic adjustment during severe water stress. Except for ‘Ghojagh’, leaves grown under severe water stress conditions showed symptoms of oxidative stress such as reduced chlorophyll concentration. The improved performance of ‘Ghojagh’ under drought stress may be associated with an efficient osmotic adjustment. The up- or down regulated expression of cytosolic glutathione reductase (cytosolic GR) and glutathione peroxidase were observed under drought conditions. Moreover, the suppressed expression of cytosolic GR was also noted. Comparatively, ‘Rabab’ exhibited higher antioxidant capacity and an efficient ROS-scavenging mechanism under drought stress. Lower levels of membrane lipid peroxidation in ‘Ghojagh’ and ‘Rabab’ under drought stress and the marked reduction of malondialdehyde concentration after re-watering represents that these cultivars have a good tolerance to drought stress. As a first step towards the study of the biochemical and molecular responses of pomegranate plants to water stress, this research provides new information into the mechanisms of drought tolerance in the plants.     

Photosynthetic limitations in response to water stress and recovery in Mediterranean plants with different growth forms

* Whether photosynthesis is limited during water stress and recovery because of diffusive or biochemical factors is still open to debate, and apparent contradictions appear when various studies on species with different growth forms are compared. * Ten Mediterranean species, representing different growth forms, were subjected to different levels of water stress, the most severe followed by rewatering. A quantitative limitation analysis was applied to estimate the effects of water stress on stomatal (S(L)), mesophyll conductance (MC(L)) and biochemical limitations (B(L)). * Results confirmed a general pattern of photosynthetic response to water stress among C(3) plants when stomatal conductance (g(s)) is used as a reference parameter. As g(s) values decreased from a maximum to approx. 0.05 mol H(2)O m(-2) s(-1), the total photosynthetic limitation rose from 0 to approx. 70%, and this was caused by a progressive increase of both S(L) and MC(L) limitations, while B(L) remained negligible. When lower values of g(s) were achieved (total photosynthetic limitation increased from 70 to 100%), the contribution of S(L) declined, while MC(L) still increased and B(L) contributed significantly (20-50%) to the total limitation. * Photosynthetic recovery of severely stressed plants after rewatering showed a dominant role of MC(L), irrespective of the degree of photosynthesis recovery.     

Stomatal numbers of soybean and response to water stress

The relationship among stomatal density, photosynthetic rate, leaf conductance, plant growth, bean yield and kaempferol triglucoside (K9) in the leaves of soybean (Glycine max (L.) Merr.) was examined in two field tests. K9 in the leaves was associated with reduced stomatal density, reduced photosynthetic rate, reduced stomatal conductance, reduced plant weight and lower bean yield. Plants with high stomatal frequency (lacking K9) were better able to take advantage of increased water supply by increasing stomatal conductance (upper surface), transpiration and bean yield. Plants with low stomatal frequency (with K9) were unresponsive to irrigation and in this sense were more tolerant of water stress, but their overall yield was low.     

Proteome analysis of cold stress response in Arabidopsis thaliana using DIGE-technology

A proteome study based on 2-D gel electrophoresis was performed in order to analyse the cold-stress response of Arabidopsis plants. The emphasis was to monitor the overall changes in the protein complement after prolonged exposure rather than short-term responses. Two different temperature regimes were used (6 degrees C and 10 degrees C) and plants were exposed to cold-stress exposure for 1 week. Protein patterns were also monitored after re-shifting plants to control conditions for a further week. To monitor gradual changes in the response to the two cold-stress conditions, the analysis was performed with DIGE technology with the inclusion of an internal standard. In the experiments using 6 degrees C, 22 spots with at least 2-fold altered expression were found; among them 18 were increased and four were decreased. When plants were exposed to 10 degrees C, 18 of these 22 spots still showed a 2-fold change; however, the alterations were, in general, more moderate than observed under 6 degrees C. Spot identification was performed by MALDI-TOF and ESI-MS/MS. Many of the proteins identified have previously been described in the context of cold-stress responses, indicating the validity of this proteome approach for further in-depth studies.     

Stomatal response of cotton to water stress and abscisic Acid as affected by water stress history

The threshold leaf water potential required to initiate stomatal closure in cotton (Stoneville 213) became progressively more negative when plants were subjected to a series of water stress cycles. The shift in the threshold water potential required for induction of stomatal closure was dependent on the number of previous stress cycles and leaf age. The basal level of endogenous abscisic acid (ABA) in fully turgid leaves increased in response to the stress treatments, whereas the amount accumulated in response to a subsequent stress did not differ greatly among plants that had experienced different degrees of stress conditioning.     

Photosynthetic response of tetraploid and hexaploid wheat to water stress

Photosynthetic characteristics of ear and flag leaves of wheat species, tetraploid Triticum dicoccoides Kom and hexaploid Bima1, were studied in plants grown under well-watered (WW) and water-stressed (WS) conditions. Compared to ears, flag leaves exhibited higher photosynthetic rate (P _N) at the filling stage, but more severe decrease under WS. P _N in the tetraploid wheat ear remained higher than that in the hexaploid wheat during the grain-filling stage. Water stress decreased PN in both the organs; this decline was caused by a reduction in Rubisco activity, not by drought-induced stomatal limitation. Tetraploid wheat ears exhibited higher relative water content and water-use efficiency than that of hexaploid wheat, under WS. The change in phosphoenolpyruvate carboxylase activity and carbon isotope composition indicated the absence of C₄ metabolism in the ears of both species under both conditions. The improved performance of the tetraploid wheat ears under WS was associated with better water relations.     

Physiological and biochemical responses of Phoebe bournei seedlings to water stress and recovery

Phoebe bournei commonly called nanmu is an important and endemic wood species in China, and its planting, nursing, and preserving are often affected by drought stress. Two-year-old P. bournei seedlings were subjected to water stress and recovery treatment to study their physiological and biochemical responses. Physiological and biochemical indices did not change when seedlings were subjected to mild water stress (<15 days of water withholding). As drought stress intensified (>20 days of water withholding), malondialdehyde and electrolyte leakage increased, and chlorophyll and soluble protein decreased, indicating an increased oxidative stress induced by water deficit. Enhanced activities of superoxide dismutase (SOD) and peroxidase (POX), accumulation of free proline and total soluble sugar contribute to plant protection against the oxidative stress. However, SOD and POX decreased when seedlings were subjected to an extended drought. After 5 days of recovery, physiological and biochemical indices were not restored to the control level values except for leaf relative water content when the seedlings were subjected to more than 20 days water stress. These results demonstrate that P. bournei could enhance their ability to mitigate water stress effects by up-regulating antioxidant system and osmotic adjustment, but these two protective mechanisms were limited when seedlings were subjected to moderate and severe water stress. The threshold of water deficit to P. bournei seedlings is 15–20 days, and permanent damage will be induced if water status is not improved before this threshold. The results will provide some theoretical and practical guidance for nanmu afforestation and production.     

Eco-physiological response to water stress of drought-tolerant and drought-sensitive tomato genotypes

Water stress is an increasing environmental constraint affecting tomato growth and yield in Mediterranean areas. Solanum pennellii is a wild tomato species that exhibits a higher water use efficiency compared with cultivated S. lycopersicum. In particular, a cultivated line carrying a small S. pennellii region on chromosome 9 (IL 9-2-5) was identified as more tolerant to water deficit. In this work, the tolerant (IL 9-2-5) and the susceptible (M82) genotypes were subjected to three different water regimes: irrigation with 100% (V1), 50% (V2) and 25% (V3) field capacity. To evaluate the physiological response of IL 9-2-5 and M82 to water deficit, leaf functional traits, plant biomass production and maximal PSII photochemical efficiency were measured together with photosynthetic pigments and phenolic compounds. The higher tolerance to water deficiency of IL 9-2-5 was associated with the development of a better antioxidant system, especially in treatment V3. In addition, IL 9-2-5 had higher values of sclerophylly and leaf dry matter content thus confirming that the tolerance of IL 9-2-5 can be attributed to traits related to leaf morphology and physiology. In future, identification of polymorphisms in key-genes controlling these traits can guide breeding efforts aimed at improving susceptible genotypes.     

Rootstock control of scion response to water stress in grapevine

Rootstocks play a major role in grapevine tolerance to water stress by controlling and adjusting the water supply to shoot transpiration demand. This study aimed to characterize the influence of rootstock genotypes in the adaptive response of scions to water limiting conditions. The effect of rootstock genotype (140Ru and SO4) was observed in the different availability of water provided to the scions (Cabernet Sauvignon, Grenache, Merlot, Syrah), while scions influenced stomatal control of water transpiration. Implication on the cell-to-cell component of plant water transport in both rootstock and scion impacted on embolisms formation in roots and on hydraulics of leaves. The main conclusion of the present study was that rootstock and scion genotypes are able to confer to the plant traits of drought adaptability influencing respectively the capacity of water extraction from the soil and the sensitivity of the stomatal control.     

Dynamic variability in thermal-germination response of squirreltail (Elymus elymoides and Elymus multisetus)

Bottlebrush squirreltail (Elymus elymoides) and big squirreltail (Elymus multisetus) have been identified as high-priority species for restoration and rehabilitation of millions of acres of rangeland in the western United States that have been degraded by wildfire and introduced annual weeds. In this study, squirreltail accessions from Idaho, Colorado, Utah, Arizona and New Mexico were grown in a nursery environment to produce seeds in two different years for germination evaluation at 11 constant temperatures. A statistical-gridding model was used to predict cumulative germination rate of each seedlot for eight simulated planting dates between 1 January and 28 May over a 38-year seedbed-microclimatic simulation. Predicted germination response under simulated conditions of field-variable temperatures yielded a broader ecological basis for the relative ranking of thermal response than was obtained from single-value germination indices derived from either constant-temperature experiments, or from analysis of thermal-time coefficients.     

Proteome plasticity in response to persistent environmental change

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Proteome analysis of Borrelia burgdorferi response to environmental change

We examined global changes in protein expression in the B31 strain of Borrelia burgdorferi, in response to two environmental cues (pH and temperature) chosen for their reported similarity to those encountered at different stages of the organism's life cycle. Multidimensional nano-liquid chromatographic separations coupled with tandem mass spectrometry were used to examine the array of proteins (i.e., the proteome) of B. burgdorferi for different pH and temperature culture conditions. Changes in pH and temperature elicited in vitro adaptations of this spirochete known to cause Lyme disease and led to alterations in protein expression that are associated with increased microbial pathogenesis. We identified 1,031 proteins that represent 59% of the annotated genome of B. burgdorferi and elucidated a core proteome of 414 proteins that were present in all environmental conditions investigated. Observed changes in protein abundances indicated varied replicon usage, as well as proteome functional distributions between the in vitro cell culture conditions. Surprisingly, the pH and temperature conditions that mimicked B. burgdorferi residing in the gut of a fed tick showed a marked reduction in protein diversity. Additionally, the results provide us with leading candidates for exploring how B. burgdorferi adapts to and is able to survive in a wide variety of environmental conditions and lay a foundation for planned in situ studies of B. burgdorferi isolated from the tick midgut and infected animals.     

Growth and physiological response of Arundo donax L. to controlled drought stress and recovery

Soil water deficit constrains crop growth more than any other abiotic stress, both per se and in combination with other factors, making drought resistance a key element for the successful exploitation of marginal areas. Arundo donax (Poaceae), is a mesophyte that can adapt to a wide variety of ecological conditions, although its growth can be retarded by a shortage of water. The objective of the present research is to draw a comprehensive picture of the integrated response mechanisms of A. donax to controlled drought conditions, and characterize its ability to recover upon rewatering in terms of photochemical efficiency. Plants were subjected to a gradually applied drought stress for a period of three weeks, after which they were returned to fully hydrated soil conditions for one week. Overall, plant dry weight and key growth parameters were not significantly affected. However, detrimental effects were visible in the form of impaired leaf gas exchange, which influences the performance of photosynthesis, and pre-dawn leaf water potential (pdΨ_W), ?92.1% of net CO₂ assimilation rate and ?0.36 MPa, respectively at the cessation of stress. Nonetheless, a rapid restoration of A. donax physiological functions was observed upon rewatering, testifying to the environmental plasticity of this species.     

Antioxidative protection in the inducible CAM plant Sedum album L. following the imposition of severe water stress and recovery

The antioxidative protection during the C₃-CAM shift induced by water stress was investigated in the temperate succulent Sedum album L. The C₃-CAM shift was characterized in terms of CO₂ exchange, titratable acidity and phosphoenolpyruvate carboxylase activity. Well-watered plants displayed C₃-like patterns of gas exchange and exhibited a mild day-night acid fluctuation indicating that those plants were performing CAM-cycling metabolism. Imposed drought highly stimulated CAM cycling, decreasing the net CO₂ uptake during the day, eliminating net CO₂ efflux at night and stimulating tissue acid fluctuations. As water deficit developed, chlorophyll fluorescence measurements showed a decrease in the Fv/Fm ratio, indicating that photoinhibition could follow after severe drought. Protection might be performed by the increased activity of enzymes involved in the destruction of free radicals and oxidants, but their response depended on the water status of the plant. Ascorbate peroxidase and superoxide dismutase activities increased in plants subjected to mild stress but declined during severe water stress. Catalase activity, however, was quite stable under mild water stress and was clearly inhibited under severe water stress. At this stage, glutathione reductase and monodehydroascorbate reductase seemed to be very important in the protection against oxidants, both increasing considerably their activities under severe water stress. Even if recycling has been shown to alleviate photoinhibition, our results clearly demonstrate that antioxidative enzymes play an important role in the protection of plants from oxidants during the C₃-CAM shift induced by water stress.     

Protein expression changes during cotton fiber elongation in response to drought stress and recovery

An investigation to better understand the molecular mechanism of cotton (Gossypium hirsutum L.) fiber elongation in response to drought stress and recovery was conducted using a comparative proteomics analysis. Cotton plants (cv. NuCOTN 33B) were subjected to water deprivation for 10 days followed by a recovery period (with watering) of 5 days. The temporal changes in total proteins in cotton fibers were examined using 2DE. The results revealed that 163 proteins are significantly drought responsive. MS analysis led to the identification of 132 differentially expressed proteins that include some known as well as some novel drought‐responsive proteins. These drought responsive fiber proteins in NuCOTN 33B are associated with a variety of cellular functions, i.e. signal transduction, protein processing, redox homeostasis, cell wall modification, metabolisms of carbon, energy, lipid, lignin, and flavonoid. The results suggest that the enhancement of the perception of drought stress, a new balance of the metabolism of the biosynthesis of cell wall components and cytoskeleton homeostasis plays an important role in the response of cotton fibers to drought stress. Overall, the current study provides an overview of the molecular mechanism of drought response in cotton fiber cells.     

Growth,water relations,and CAM induction inSedum album in response to water stress

Growth analysis indicated that carbon gain in the alpine succulentSedum album tended to take place early during the growing season. Leaf water potential remained unchanged for a considerable length of time after the imposition of water stress in the field. Induction of crassulacean acid metabolism (CAM) by protracted water stress occurred before any signs of stress could be observed in the leaves, and appeared to be influenced by a complex interaction of environmental conditions including temperature and duration of sunshine. Increased levels of proline and betaine towards the end of the growing season appeared to reflect seasonal changes.     

Proteome analysis of soybean roots subjected to short-term drought stress

Drought is one of the most important constraints on the growth and productivity of many crops, including soybeans. However, as a primary sensing organ, the plant root response to drought has not been well documented at the proteomic level. In the present study, we carried out a proteome analysis in combination with physiological analyses of soybean roots subjected to severe but recoverable drought stress at the seedling stage. Drought stress resulted in the increased accumulation of reactive oxygen species and subsequent lipid peroxidation. The proline content increased in drought-stressed plants and then decreased during the period of recovery. The high-resolution proteome map demonstrated significant variations in about 45 protein spots detected on Comassie briliant blue-stained 2-DE gels. Of these, 28 proteins were identified by mass spectrometry; the levels of 5 protein spots were increased, 21 were decreased and 2 spots were newly detected under drought condition. When the stress was terminated by watering the plants for 4 days, in most cases, the protein levels tended towards the control level. The proteins identified in this study are involved in a variety of cellular functions, including carbohydrate and nitrogen metabolism, cell wall modification, signal transduction, cell defense and programmed cell death, and they contribute to the molecular mechanism of drought tolerance in soybean plants. Analysis of protein expression patterns revealed that proteins associated with osmotic adjustment, defense signaling and programmed cell death play important roles for soybean plant drought adaptation. The identification of these proteins provides new insight that may lead to a better understanding of the molecular basis of the drought stress responses.     

不同甘蔗品种叶片气孔对水分胁迫的响应

干旱是甘蔗面临最主要的环境胁迫之一,为了解不同甘蔗品种在干旱胁迫时的气孔响应,该研究以F172、GT21、YT93/159和 YL6四个抗旱性有显著差异的甘蔗品种为材料,采用桶栽,在伸长期进行四种不同程度的干旱胁迫(不浇水)处理：土壤持水量在①65％~70％为轻度干旱;②45％~50％为中度干旱;③25％~30％为重度干旱;④以土壤含水量为75％为对照(CK).检测不同品种不同处理甘蔗的叶片相对持水量变化,并利用扫描电镜技术观察甘蔗叶片下表皮气孔特性.结果表明：在干旱胁迫下,四个甘蔗品种叶片气孔导度急剧下降,重度干旱时耐旱性强的 F172和 GT21的气孔导度低于耐旱性弱的 YT93/159和 YL6的;复水后3 d,F172和 GT21的气孔导度上升至82．07和88．85 mmol·m-2·s-1,而 YT93/159和 YL6的仅有18．88和33．08 mmol·m-2·s-1.干旱还导致气孔下陷、闭合,气孔器的长、宽明显减小,且品种间气孔器长度变化差异显著;干旱胁迫下气孔密度增大,尤以耐旱性最强的 F172在重度干旱时达到显著差异.重度干旱时 F172与GT21的气孔闭合百分比是 YT93/159和 YL6近3~4倍.在水分胁迫下,叶片相对含水量降低,但 F172和GT21在重度干旱时仍可以保持相对较高的含水量,其它两个品种相对较低,尤以 YT93/159的最低.在复水后叶片含水量都有所恢复.这些研究结果表明不同甘蔗品种抗旱能力与叶片气孔特性和含水量密切相关.