The responses of Briza media and Koeleria macrantha to drought and re-watering

1. To test whether differences in response to drought can help to explain the differing distributions of Briza media and Koeleria macrantha , changes in their leaf growth and water relations during soil drying were measured. After droughting, plants were re-watered and recovery recorded.
2. Leaf growth of the two species showed a similar sensitivity to drought with respect to duration of soil drying and soil moisture content.
3. In both species tiller base relative water content (RWC) was maintained at similar levels to controls until soil moisture content had fallen to less than 9%. This may aid survival in habitats subject to periodic droughting by preventing damage to the meristems.
4. Briza media did not respond to re-watering. However, plants of K. macrantha re-grew after periods of over 20 days of drought, when tiller base RWCs had fallen as low as 13%. This ability to resurrect may explain the occurrence of K. macrantha in xeric calcicolous grasslands subject to episodes of severe droughting, from which B. media is absent.     

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.     

The influence of signals from chilled roots on the proteome of shoot tissues in rice seedlings

Low root temperature causes a decrease in water uptake, which leads to mineral and nutrient deficiencies with potentially decreased root and shoot growth. Differential temperature effects in plants have been studied extensively, however, the effect of root chilling on the global protein expression in shoots has not been explored. In this study, we imposed chilling temperatures on roots of rice plants while maintaining shoots at optimum atmospheric temperature. Shoot materials (growing zones and leaves) were harvested at five points over a time course of four days, including a two‐day recovery period. Proteins were quantified by tandem mass tags and triple stage MS, using a method developed to overcome ratio compression in isobaric‐labelled quantitation. Over 3000 proteins in each of the tissues were quantified by multiple peptides. Proteins significantly differentially expressed as compared with the control included abscisic acid‐responsive and drought‐associated proteins. The data also contained evidence of a possible induction of a sugar signalling pathway.     

Changes of photosynthetic traits in beech saplings (Fagus sylvatica) under severe drought stress and during recovery

In the context of an increased risk of extreme drought events across Europe during the next decades, the capacity of trees to recover and survive drought periods awaits further attention. In summer 2005, 4-year-old beech (Fagus sylvatica L.) saplings were watered regularly or were kept for 4 weeks without irrigation in the field and then re-watered again. Changes of plant water status, leaf gas exchange and Chl a fluorescence parameters, as well as alterations in leaf pigment composition were followed. During the drought period, stomatal conductance (g(s)) and net photosynthesis (P(n)) decreased in parallel with increased water deficit. After 14 days without irrigation, stomata remained closed and P(n) was almost completely inhibited. Reversible downregulation of PSII photochemistry [the maximum quantum efficiency of PSII (F(v)/F(m))], enhanced thermal dissipation of excess excitation energy and an increased ratio of xanthophyll cycle pigments to chlorophylls (because of a loss of chlorophylls) contributed to an enhanced photo-protection in severely stressed plants. Leaf water potential was restored immediately after re-watering, while g(s), P(n) and F(v)/F(m) recovered only partially during the initial phase, even when high external CO(2) concentrations were applied during the measurements, indicating lasting non-stomatal limitations. Thereafter, P(n) recovered completely within 4 weeks, meanwhile g(s) remained permanently lower in stressed than in control plants, leading to an increased 'intrinsic water use efficiency' (P(n)/g(s)). In conclusion, although severe drought stress adversely affected photosynthetic performance of F. sylvatica (a rather drought-sensitive species), P(n) was completely restored after re-watering, presumably because of physiological and morphological adjustments (e.g. stomatal occlusions).     

Differentially expressed proteins associated with drought tolerance in bananas (<Emphasis Type="Italic">Musa</Emphasis> spp.)

Bananas are one of the most important fruits in tropical and subtropical regions worldwide. Each year, banana plantations expand, but the areas available are mostly dry lands. The establishment of strategies for obtaining drought tolerant cultivars depends on understanding of biological responses at genetic, molecular and biochemical levels. Proteomics is a powerful tool for functional characterization of the response of plants to abiotic stress and little is known about drought tolerance in Musa spp. Therefore, the aim of this study was to identify proteins related to drought tolerance in two contrasting banana genotypes, Prata Anã and BRS Tropical, susceptible and tolerant to drought, respectively. Proteins were extracted from rhizomes of bananas grown under greenhouse conditions with control, irrigated and water deficit regimes. The differential protein expression pattern was established by two-dimensional (2-D) electrophoresis and spots analyzed in nano Q-Tof Micro UPLC. Twenty-three differentially expressed proteins were found in the tolerant genotype (BRS Tropical) under water deficit, with proteins involved in metabolism, defense and transport. Proteins were classified according to known function and biosynthetic pathways. Signaling proteins in response to water stress, especially for the biological function of growth and development of plants cells, were also encountered, whereas heat shock proteins played a significant role. This is the first report of proteomic analysis for drought tolerance in ‘Pome’ and ‘Silk-type’ bananas containing the ‘B’ genome. Our work provides insights into Musa spp. response to drought and data for further studies regarding molecular mechanisms, which determine how Musa spp. cells better overcome environmental perturbations.     

Photosynthetic characteristics in different peanut cultivars under conditions of drought and re-watering at seedling stage

Aims In China, peanut (Arachis hypogaea) is mainly cultivated in the semi-arid and rain-fed areas, and drought is the most prominent environmental stress to its growth. However, studies on the physiological responses of different peanut cultivars to drought and re-watering are lacking. Our objectives were to investigate the relationship between photosynthetic characteristics and drought tolerance, and to explore the ability to recover from drought damage in different peanut cultivars.
Methods A pot experiment was conducted with artificial water stress treatment, and the photosynthetic characteristics were determined in twelve peanut cultivars under the conditions of drought stress and re-watering at the seedling stage. The drought tolerance was assessed by drought resistance coefficient of biomass in seedling. The recovery capacity was assessed by compensatory growth of plant.
Important findings Five cultivars, including ‘Shanhua 11’, ‘Rugaoxiyangsheng’, ‘A596’, ‘Shanhua 9’, and ‘Nongda 818’, showed over-compensatory growth after re-watering, and their capacity of compensatory growth had significant positive correlation with drought tolerance (p < 0.01). The net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), maximum photochemical efficiency (F_v/F_m), PSII actual quantum yield (ΦPSII), and photochemical quenching coefficient (q_P) all decreased over the course of drought stress, and then increased following re-watering, with the amplitude of changes being smaller in the more drought tolerant cultivars. Seven days of drought did not result in significant differences in the photosynthetic characteristics among majority of the peanut cultivars tested (p > 0.05). After 14 days of drought, the values of photosynthetic variables differed significantly among the peanut cultivars with different drought tolerance (p < 0.05). The values of P_n, G_s, Φ_PSII, F_v/F_m, and q_P in the cultivars ‘Shanhua 11’, ‘Rugaoxiyangsheng’, ‘A596’, and ‘Shanhua 9’fully recovered five days after re-watering, while those in the cultivars ‘79266’, ‘ICG6848’, ‘Baisha 1016’, and ‘Hua 17’ did not fully recover even after 10 days of re-watering; the values of those photosynthetic variables were significantly greater (p < 0.05) in the more drought tolerant cultivars following re-watering. Correlation analysis showed that the drought tolerance was significantly and positively correlated with P_n, Φ_PSII, F_v/F_m, and q_P after 14 days of drought stress and after five days of re-watering, respectively (p < 0.01). Therefore, under drought stress at 40% of relative water content (RWC) for 14 days and after five days of re-watering at the seedling stage, the P_n, Φ_PSII, F_v/F_m, and q_P could be used for identifying the level of damage and recovery capacity of peanut cultivars. The cultivar ‘Shanhua 11’ can be used as a reference for drought adaptability identification in peanut.     

马铃薯块茎膨大期不同程度干旱后复水的源库补偿效应

旱后复水的补偿效应在多种作物的不同生育时期都存在,是植物抵抗逆境胁迫和伤害的重要自我调节机制,也是对有限水分高效利用的体现.本研究在马铃薯块茎膨大期进行两轮干旱后复水处理,明确马铃薯补偿效应产生的干旱胁迫阈值,并从源-库角度探索马铃薯旱后复水补偿效应产生的缘由.试验选取‘大西洋’马铃薯脱毒组培苗为材料,设置充分供水(W)、轻度干旱后复水(D₁-W)、中度干旱后复水(D₂-W)和重度干旱后复水(D₃-W)4个水分处理并经过两个循环.结果表明:在经过两轮轻度干旱复水后,马铃薯产量表现出超补偿效应,水分利用效率和产量比充分供水分别提高了17.5%和6.3%;中度水分胁迫表现出近等量补偿效应,产量与充分供水差异不大,而水分利用效率提高了8.4%;而重度水分胁迫没有表现出产量补偿效应.不同程度的干旱胁迫均降低马铃薯叶片叶绿素含量、净光合速率、叶面积等源的大小和活性,而在复水后,轻度和中度胁迫出现了超补偿和补偿效应,增强了源的供应能力.同时,适度干旱后复水显著增强了块茎(库)中蔗糖-淀粉代谢途径关键酶的活性,提高了库活性,进而表现为块茎平均重量的增加.综上,马铃薯块茎膨大期适度的水分亏缺在复水后源-库均存在补偿和超补偿效应,以此来弥补干旱带来的损失,最终在产量上表现为补偿或者超补偿效应,并显著提高了水分利用效率.     

苗期干旱及复水条件下不同花生品种的光合特性

为探索不同花生(Arachis hypogaea)品种的旱后恢复能力, 研究花生品种耐旱性与光合特性的关系, 通过盆栽土壤水分控制实验, 测定了12个花生品种苗期对干旱胁迫与复水过程的光合响应特征, 并讨论了所测各性状参数与抗旱性强弱的关系, 包括对水分胁迫伤害的修复能力。结果表明, 根据苗期生物量抗旱系数, ‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’、‘农大818’的抗旱性较强, 且复水后植株产生超补偿生长效应, 补偿生长能力与抗旱性呈极显著正相关。叶片净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、最大光化学效率(F_v/F_m)、实际光化学效率(Φ_PSII)、光化学猝灭系数(q_P)随干旱进程逐渐降低, 复水后逐渐增加, 抗旱性强的花生品种变幅较小。干旱7天, 大多数花生品种的光合参数值未有显著性差异。干旱14天, 抗旱性越强的花生品种光合参数值越高, 不同抗旱性花生品种的光合参数值有显著差异。‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’的P_n、G_s、Φ_PSII、F_v/F_m、q_P在复水5天时恢复至对照水平, 复水10天时超过对照, ‘79266’、‘ICG6848’、 ‘白沙1016’、‘花17’在复水10天时仍未达到对照水平, 复水过程中抗旱性强的品种的光合参数显著高于抗旱性弱的品种。相关分析表明, 干旱胁迫14天和复水5天后, 花生的P_n、Φ_PSII、F_v/F_m、q_P与品种抗旱性呈极显著正相关。因此, 可在苗期用40%土壤相对含水量胁迫14天及复水5天时花生的P_n、Φ_PSII、F_v/F_m、q_P鉴定品种的干旱伤害程度及修复能力, ‘山花11号’可作为强干旱适应性鉴定的标准品种。     

干旱胁迫条件下马铃薯耐旱品种宁蒗182叶片蛋白质组学分析

开展马铃薯抗旱分子机理的研究对培育马铃薯抗旱品种, 减少干旱造成的损失至关重要。文章利用双向电泳技术对云南地方耐旱马铃薯品种宁蒗182在干旱与正常处理条件下叶片表达差异蛋白质组进行对比研究。经电泳图谱分析和MALDI-TOF-TOF/MS质谱鉴定获得12个表达差异蛋白点, 并进行了功能分类。结果发现, 在差异蛋白中具有保护马铃薯光和系统以及线粒体正常运转的酶类; 调节该植株对环境胁迫响应的信号传导以及调控其组织内N、C运输系统的功能蛋白, 这些蛋白在受到干旱胁迫时表达量均升高。这一结果揭示出该类蛋白是马铃薯在干旱条件下产生的耐受相关蛋白。文章为阐释马铃薯抗旱品种通过多种路径和水平的调控提高其抗性的分子机理提供了理论依据。     

Beyond osmolytes and transcription factors: drought tolerance in plants <Emphasis Type="Italic">via</Emphasis> protective proteins and aquaporins

Mechanisms of drought tolerance have been studied by numerous groups, and a broad range of molecules have been identified to play important roles. A noteworthy response of stressed plants is the accumulation of novel protective proteins, including heat-shock proteins (HSPs) and late embryogenesis abundant (LEA) proteins. Identification of gene regulatory networks of these protective proteins in plants will allow a wide application of biotechnology for enhancement of drought tolerance and adaptation. Similarly, aquaporins are involved in the regulation of water transport, particularly under abiotic stresses. The molecular and functional characterization of protective proteins and aquaporins has revealed the significance of their regulation in response to abiotic stresses. Herein, we highlight new findings regarding the action mechanisms of these proteins. Finally, this review also surveys the current advances in engineering drought tolerant plants, particularly the engineering of protective proteins (sHSPs and LEA) and aquaporins for imparting drought stress tolerance in plants.     

MusaDHN-1, a novel multiple stress-inducible SK3-type dehydrin gene, contributes affirmatively to drought- and salt-stress tolerance in banana

Dehydrins are highly hydrophilic proteins involved in playing key adaptive roles in response to abiotic stress conditions having dehydration as a common component. In the present study, a novel banana SK(3)-type dehydrin, MusaDHN-1, was identified and later characterized using transgenic banana plants to investigate its functions in abiotic stress tolerance. Expression profiling in native banana plants demonstrated that MusaDHN-1 was induced in leaves by drought, salinity, cold, oxidative and heavy metal stress as well as by treatment with signalling molecules like abscisic acid, ethylene and methyl jasmonate. Promoter analysis carried out by making a MusaDHN-1 promoter: β-glucuronidase fusion construct reconfirmed the abiotic stress inducibility of MusaDHN-1. Transgenic banana plants constitutively overexpressing MusaDHN-1 were phenotypically normal and displayed improved tolerance to drought and salt-stress treatments in both in vitro and ex vitro assays. Enhanced accumulation of proline and reduced malondialdehyde levels in drought and salt-stressed MusaDHN-1 overexpressing plants further established their superior performance in stressed conditions. This study is the first to report generation of transgenic banana plants engineered for improved drought and salt-stress tolerance.     

Rubisco and some chaperone protein responses to water stress and rewatering at early seedling growth of drought sensitive and tolerant wheat varieties

Four wheat varieties differing in their drought tolerance were subjected to severe but recoverable water stress at seedling stage. Growth parameters, leaf water deficit (WD) and electrolyte leakage (EL) were used to evaluate the stress intensity and the extent of recovery. The physiological response of the varieties was quite similar under severe drought. Leaf protein patterns and levels of some individual proteins relevant to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) maintenance were studied in control, stressed and recovering plants by electrophoresis and immunoblotting. The bands representing Rubisco large subunit (RLS), N- and C-terminus of RLS, Rubisco activase (RA) and Rubisco binding protein (RBP, cpn 60), as well as the chaperone and proteolytic subunits of the Clp protease complex were identified using polyclonal antibodies. Under drought conditions RLS, Clp proteases and especially RBP were enhanced, whereas the RA band was only slightly affected. The drought tolerant varieties had higher RBP content in the controls and drought treated plants. Its concentration could be a potential marker for drought tolerance.     

A root proteomics-based insight reveals dynamic regulation of root proteins under progressive drought stress and recovery in <Emphasis Type="Italic">Vigna radiata</Emphasis> (L.) Wilczek

To understand the complex drought response mechanism in crop plants, a systematic root proteomics approach was adopted to identify and analyze the expression patterns of differentially expressed major root proteins of Vigna radiata during short-term (3 days) and consecutive long-term water-deficit (6 days) as well as during recovery (6 days after re-watering). Photosynthetic gas exchange parameters of the plant were measured simultaneously during the stress treatment and recovery period. A total of 26 major protein spots were successfully identified by mass spectrometry, which were grouped according to their expression pattern during short-term stress as significantly up-regulated (9), down-regulated (10), highly down-regulated, beyond detection level of the software (2) and unchanged (5). The subsequent changes in the expression patterns of these proteins during long-term stress treatment and recovery period was analyzed to focus on the dynamic regulation of these functionally important proteins during progressive drought and recovery period. Cytoskeleton-related proteins were down-regulated initially (3d) but regained their expression levels during subsequent water-deficit (6d) while glycoprotein like lectins, which were primarily known to be involved in legume–rhizobia symbiosis, maintained their enhanced expression levels during both short and long-term drought treatment indicating their possible role in drought stress response of legumes. Oxidative stress-related proteins including Cu/Zn superoxide dismutase, oxidoreductase and aldehyde reductase were also up-regulated. The analyses of the dynamic regulation of these root proteins during short- and long-term water-deficit as well as recovery period may prove crucial for further understanding of drought response mechanisms in food legumes.     

Probing the responses of barley cultivars (Hordeum vulgare L.) by chlorophyll a fluorescence OLKJIP under drought stress and re-watering

The main objective of this study was to evaluate the effects of drought and re-watering on 10 varieties of barley (Hordeum vulgare L.) originating from Morocco. Five varieties obtained from the National Institute of Agricultural Research (INRA) of Morocco and five landraces (local varieties defined by high stress tolerance, high yield stability, an intermediate yield and low-input demand) collected at five localities in the south of Morocco were used in the present study. After 2 weeks of growth, drought stress was initiated by withholding water for 2 weeks followed by 1 week of re-watering. The polyphasic OJIP fluorescence transient was used to evaluate photosystem II (PSII) criteria at the end of the first week of drought stress (moderate drought), at the end of the second week (severe drought) and the end of the recovery phase. Drought and re-watering had little effect on the maximum quantum yield of primary photochemistry φ_Po(=F_V/F_M). The photosynthetic performance index (PI) is the product of an antenna, reaction center and electron transport dependent parameter. It revealed differences between varieties as a function of drought and re-watering. For the screening for drought stress tolerance, changes in the PI during a 2-week drought stress treatment were analysed and a new parameter was defined: the drought factor index (DFI) = log(PI_week 1/PI_control) + 2 log(PI_week 2/PI_control). The DFI of the tested varieties correlated with their drought tolerance. Another parameter that was analysed was the relative water content. It decreased during the drought stress treatment varying between 61% and 78.2% at the end of the drought period. During the subsequent recovery period, it increased in a species-dependent manner (65.1–94.1%). A third parameter studied were changes in the initial fluorescence rise. The fluorescence rise during the first 300 μs (L-band) can give information on the energetic connectivity between PSII units whereas changes in the rise during the first 2 ms (K-band) offer information on developing limitations on the donor side of PSII. Changes in respectively the L and K-bands of the fluorescence transients OJIP were shown to have predictive value with respect to the vitality of leaves and the tolerance of the varieties to drought stress.     

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.     

gid1, a gibberellin-insensitive dwarf mutant, shows altered regulation of probenazole-inducible protein (PBZ1) in response to cold stress and pathogen attack

A recessive gibberellin (GA)-insensitive dwarf mutant of rice, gibberellin-insensitive dwarf1 (gid1), has been identified, which shows a severe dwarf phenotype and contains high concentrations of endogenous GA. To elucidate the function of gid1, proteins regulated downstream of gid1 were analysed using a proteomic approach. Proteins extracted from suspension-cultured cells of gid1 and its wild type were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Of a total of 962 proteins identified from the suspension-cultured cells, 16 were increased and 14 were decreased in gid1 compared with its wild type. Among the proteins hyper-accumulated in gid1 were osmotin, triosephosphate isomerase, probenazole inducible protein (PBZ1) and pathogenesis-related protein 10. Of these four genes, only the expression of PBZ1 was increased by exogenous GA3 application. Expression of this gene was also enhanced in shoots of the wild type by cold stress or by rice blast fungus infection. Under normal growth conditions, there was more PBZ1 protein in gid1 than in the wild type. In addition, gid1 showed increased tolerance to cold stress and resistance to blast fungus infection. The entcopalyl diphosphate synthase (OsCPS) genes, which encode enzymes at the branch point between GA and phytoalexin biosynthesis, were expressed differentially in gid1 relative to the wild type. Specifically, OsCPS1, which encodes an enzyme in the GA biosynthesis pathway, was down-regulated and OsCPS2 and OsCPS4, which encode enzymes in phytoalexin biosynthesis, were up-regulated in gid1. These results suggest that the expression of PBZ1 is regulated by GA signalling and stress stimuli, and that gid1 is involved in tolerance to cold stress and resistance to blast fungus.