植物应对干旱胁迫的阶段性策略

干旱是影响植物生存、生长和分布的最重要的非生物胁迫之一,全球暖干化将加剧干旱胁迫.植物对干旱胁迫的响应和适应机制一直是
学术研究的热点领域.本文综述了植物应对干旱胁迫的生长和生理响应,在已有的研究结果基础上,提出了植物应对干旱胁迫的阶段性响应策略.从干旱开始到干旱致死,植物经历了干旱开始-轻度干旱-中度干旱-严重干旱-极端干旱5个阶段,分别对应着应激响应-主动适应-被动适应3种响应方式和适应机制.不同阶段中植物抗旱机制的核心任务不同.最后提出了研究植物阶段性响应策略需要解决的关键科学问题及研究方向.     

植物应对干旱胁迫的气孔调节

气孔是植物控制叶片与大气之间碳、水交换的重要门户,植物的生长和生存都依赖于叶片气孔对碳获取和水散失的调控.因此,气孔调节机理研究与气孔导度模型研发是精确模拟陆地生态系统碳、水循环过程不可或缺的内容.近年来,随着气候变化的加剧,干旱事件愈发频繁,对植物的存活、生长和分布产生深刻影响.为了深入理解植物碳-水耦合机理过程、预测全球变化下植物及群落的动态,开展植物应对干旱胁迫的气孔调节研究尤为重要.本文综述了植物在干旱胁迫条件下气孔调节机制和模型研究进展.首先阐述了植物气孔对干旱胁迫的主动调节与被动调节,讨论了气孔调节的演化过程,包括蕨类和石松类植物的被动水力调节、被子植物的主动调节和裸子植物的双重调节机制,认为裸子植物的气孔调节方式是植物进化过程中介于蕨类、石松类植物和被子植物之间的一种重要过渡类型.然后分析了气孔调节与水力调节的关系,讨论了“植物水势和气孔导度解耦”问题中存在的争议.之后介绍了基于水分利用效率假说和最大碳增益假说所建立的气孔导度优化模型的应用,并指出后者有更强的预测能力和应用前景.最后,为了有效减少植被对气候变化响应预测中的不确定性,提出了2个亟待开展的研究问题:将植物叶片的气孔调节功能研究由个体扩展到生态系统甚至更大尺度,改进陆地生态系统碳水循环机理模型;量化气孔调节的主动水力反馈过程,修正植物气孔功能水力模型.     

Identification of drought tolerance determinants by genetic analysis of root response to drought stress and abscisic Acid

Drought stress is a common adverse environmental condition that seriously affects crop productivity worldwide. Due to the complexity of drought as a stress signal, deciphering drought tolerance mechanisms has remained a major challenge to plant biologists. To develop new approaches to study plant drought tolerance, we searched for phenotypes conferred by drought stress and identified the inhibition of lateral root development by drought stress as an adaptive response to the stress. This drought response is partly mediated by the phytohormone abscisic acid. Genetic screens using Arabidopsis (Arabidopsis thaliana) were devised, and drought inhibition of lateral root growth (dig) mutants with altered responses to drought or abscisic acid in lateral root development were isolated. Characterization of these dig mutants revealed that they also exhibit altered drought stress tolerance, indicating that this root response to drought stress is intimately linked to drought adaptation of the entire plant and can be used as a trait to access the elusive drought tolerance machinery. Our study also revealed that multiple mechanisms coexist and together contribute to whole-plant drought tolerance.     

木本植物水力系统对干旱胁迫的响应机制

干旱导致树木死亡对生态系统功能和碳平衡有重大影响。植物水分运输系统失调是引发树木死亡的主要机制。然而, 树木对干旱胁迫响应的多维性和复杂性, 使人们对植物水分运输系统在极端干旱条件下的响应以及植物死亡机理的认识还不清楚。该文首先评述衡量植物抗旱性的指标, 着重介绍可以综合评价植物干旱抗性特征的新参数——气孔安全阈值(SSM)。SSM越高, 表明气孔和水力性状之间的协调性越强, 木质部栓塞的可能性越低, 水力策略越保守。然后, 阐述木本植物应对干旱胁迫的一般响应过程。之后, 分别综述植物不同器官(叶、茎和根)对干旱胁迫的响应机制。植物达到死亡临界阈值的概率和时间, 取决于相关生理和形态学特征的相互作用。最后, 介绍木本植物水力恢复机制, 并提出3个亟待开展的研究问题: (1)改进叶片水分运输(木质部和木质部外水力导度)的测量方法, 量化4种不同途径的叶肉水分运输的相对贡献; (2)量化叶片表皮通透性变化, 以便更好地理解植物水分利用策略; (3)深入研究树木水碳耦合机制, 将个体结构和生理特征与群落/景观格局和过程相关联, 以便更好地评估和监测干旱诱导树木死亡的风险。     

The rhizosheath: a potential root trait helping plants to tolerate drought stress

Plant and Soil - Experimental data concerning possible trophic relationships between phorophytes and epiphytes are contradictory. Several studies have indirectly shown that epiphytes affect the...     

Nitrogen application enhanced the expression of developmental plasticity of root systems triggered by mild drought stress in rice

Background

The promoted root growth under developmental plasticity triggered specifically by mild drought stress (MDS) is known to contribute to maintained water uptake and dry matter production (DMP).

Aims

To examine whether the expression of developmental plasticity of root systems and its contribution to DMP would be affected by the levels of nitrogen (N) application.

Methods

Two genotypes (CSSL50 derived from Nipponbare/Kasalath cross and Nipponbare) were grown under soil moisture gradients with a line source sprinkler system. Three N fertilizer treatments were used; 25 (low), 75 (standard) and 150 kg N ha^?1 (high) in 2009 and 60 (low), 120 (standard) and 180 kg N ha^?1 (high) in 2011.

Results

Across varying N level treatments, there were no significant differences in any of the traits examined between the two genotypes under well-watered and severe drought stress conditions. In contrast, under MDS conditions (15–25 % w/w of soil moisture content (SMC) in 2009 and 17–25 % w/w of SMC in 2011), CSSL50 showed greater DMP than Nipponbare. The difference, however, varied with N level treatments since CSSL50’s greater root system development under MDS, was more pronounced at standard and high N levels than at low N level than it was for Nipponbare.

Conclusions

N application enhanced the expression of plasticity in root system development at standard and high N levels as compared with low N level under MDS conditions, which contributed to the maintenance of DMP.     

Responses of antioxidant systems to lanthanum nitrate treatments in tomato plants during drought stress

Abstract

Lanthanum is one of the most abundant elements in rare earths enriched fertilizers and is supposed to be one of the main responsible of the effects of such fertilizers on crops. In this work, the effect of lanthanum nitrate on H₂O₂ production, lipid peroxidation, ascorbate and glutathione content, and on the activity of cytosolic ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase in Lycopersicon esculentum L. cv. Marmande during drought stress was evaluated. The results confirmed that treatments of tomato plants with lanthanum nitrate affect the antioxidant cellular defences and that lanthanum toxicity is dependent on the way of treatment. The stimulation of antioxidant systems did not induce any improvement in drought stress responses in tomato but seemed to be only a consequence of the unbalance in cell metabolism due to the treatment with lanthanum nitrate.     

Proteomic analysis of drought-responsive proteins in rice reveals photosynthesis-related adaptations to drought stress

Drought stress inhibits rice growth and biomass accumulation. To identify novel regulators of drought-stress responses in rice, we conducted a proteome-level study of the stress-susceptible (SS) Oryza sativa L. cv. ‘Leung Pratew 123’ and its stress-resistant (SR) somaclonal mutant line. In response to osmotic-stress treatments, 117 proteins were differentially accumulated, with 62 and 49 of these proteins detected in the SS and SR rice lines, respectively. There were six proteins that accumulated in both lines. The proteins in the SS line were mainly related to metabolic processes, whereas the proteins identified in the SR line were primarily related to retrotransposons. These observations suggest that retrotransposons may influence the epigenetic regulation of gene expression in response to osmotic stress. To identify the biological processes associated with drought tolerance in rice, we conducted a co-expression network analysis of 55 proteins that were differentially accumulated in the SR line under osmotic-stress conditions. We identified a major hub gene; LOC_Os04g38600 (encoding a glyceraldehyde-3-phosphate dehydrogenase), suggesting that photosynthetic adaptation via NADP(H) homeostasis contributes to drought tolerance in rice.     

磷高效水稻根系对低磷胁迫响应的差异蛋白分析

以IR71331为材料,通过水培试验,采用双向电泳分离不同磷浓度下（低磷浓度为0.5 mg·L^-1,对照为10 mg·L^-1）水稻生长3 d和6 d根系差异蛋白.结果表明：与对照相比,低磷胁迫下共有29个蛋白,其中3 d时间点有17个蛋白上调、11个下调、1个新增,6 d时间点有8个上调、19个下调、1个抑制表达、1个无明显变化 .经鉴定,其中的10个差异表达蛋白可归为信号转导相关蛋白、基因表达相关蛋白、代谢相关蛋白离子转运相关蛋白4个功能类群.信号转导相关蛋白分别为富含甘氨酸RNA结合蛋白和类似参与磷酸盐饥饿反应调控子;基因表达相关蛋白分别为推定的mRNA前体剪接因子SF2和推定的AAA蛋白酶家族FtsH;代谢相关蛋白分别为腺苷酸琥珀酸裂解酶、丝氨酸蛋白酶抑制剂(serpin)、S-腺苷蛋氨酸合成酶（SAM）和类似MYB类转录因子;离子转运相关蛋白分别为阳离子转运ATP酶和肌浆网膜蛋白.这些蛋白分别参与了信号识别、信号调控、mRNA 的剪接、信号传递、蛋白质降解、细胞体内离子转运和平衡等生理过程.其中serpin、SAM和MYB类转录因子是水稻响应低磷胁迫的关键蛋白.水稻根系对低磷胁迫存在着一个复杂的抗逆信号应答和代谢调控网络,其作用机理可以通过差异表达的蛋白质得以体现.     

Proteomic analysis of rice leaf sheath during drought stress

Drought is one of the most severe limitations on the productivity of rainfed lowland and upland rice. To investigate the initial response of rice to drought stress, changes in protein expression were analyzed using a proteomic approach. Two-week-old rice seedlings were exposed to drought conditions from 2 to 6 days, and proteins were extracted from leaf sheaths, separated by two-dimensional polyacrylamide gel electrophoresis and stained with Coomassie brilliant blue. After drought stress for 2 to 6 days, 10 proteins increased in abundance and the level of 2 proteins decreased. The functional categories of these proteins were identified as defense, energy, metabolism, cell structure, and signal transduction. In addition to drought stress, accumulations of protein were analyzed under several different stress conditions. The levels of an actin depolymerizing factor, a light harvesting complex chain II, a superoxidase dismutase and a salt-induced protein were changed by drought and osmotic stresses, but not cold or salt stresses, or abscisic acid treatment. The effect of drought stress on protein in the leaf sheaths of drought-tolerant rice cultivar was also analyzed. The light harvesting complex chain II and the actin depolymerizing factor were present at high levels in a drought-tolerant rice cultivar before stress application. With drought stress, actin depolymerizing factor was expressed in leaf blades, leaf sheaths, and roots. These results suggest that actin depolymerizing factor is one of the target proteins induced by drought stress.     

Root plasticity as the key root trait for adaptation to various intensities of drought stress in rice

Roots play an important role in rice adaptation to drought conditions. This study aimed to identify the key root traits that contribute to plant adaptation to drought stress. We used chromosome segment substitution lines (CSSLs) derived from Nipponbare and Kasalath crosses, which were grown in the field and hydroponics. In field experiments, the plants were grown under soil moisture gradients with line source sprinkler system up to around heading. Among the 54 CSSLs, only CSSL50 consistently showed significantly higher shoot dry matter production than its parent Nipponbare as the drought intensified for 3?years while most of the CSSLs reduced dry matter production to similar extents with Nipponbare under the same conditions. CSSL50 showed significantly greater total root length through promoted lateral root branching and elongation than Nipponbare, especially under mild stress conditions (15?30% w/w of soil moisture contents), which is considered as phenotypic plasticity. Such plastic root development was the key trait that effectively contributed to plant dry matter production through increased total root length and thus water uptake. However, there was no relationship between root plasticity and plant growth under the stress conditions induced by polyethylene glycol in hydroponics.     

植物根边缘细胞的抗逆性研究进展

综述了近几年来国内外有关植物根边缘细胞抗逆性方面的研究,重点概述植物根边缘细胞对生物与非生物胁迫的响应及其相应的抗性机理。在生物胁迫下,边缘细胞能吸引和固定病原根结线虫,排斥或约束致病性细菌,可作为真菌感染的假目标,减少或避免各种病原菌对根尖的伤害。在非生物胁迫下,边缘细胞通过分泌粘液、诱导ROS产生刺激细胞死亡以抵抗铝毒,并通过其数量的改变来调节高温、高浓度CO2等多种生理反应。最后在当前植物根边缘细胞研究的基础上,提出了今后的研究方向。     

Maize root responses to drought stress depend on root class and axial position

In this study we tested the hypotheses that root classes would exhibit distinctive anatomical and architectural responses to drought stress, and that those responses would vary along the root axes. The root systems of four maize (Zea mays L.) sweet corn genotypes designated SC1, SC2, SC3 and SC4 were phenotyped under well-watered and drought treatments in greenhouse mesocosms, permitting increasing stratification of moisture availability as the drought progressed. Anatomical and architectural responses to drought were evaluated for each root class. Lignin distribution was assessed by image processing of UV-illuminated root cross-sections acquired by laser ablation tomography. The two cultivars with less biomass reduction under drought, SC3 and SC4, substantially enhanced lateral root development along the apical segments of axial roots when plants were grown with drought stress. These segments grew into the deeper part of the mesocosm where more moisture was available. Apical segments of the axial and large lateral roots from drought-stressed plants were thicker and had greater theoretical axial water conductance than basal segments, especially in SC3 and SC4. Basal segments of crown roots of SC3 and SC4 showed increased lignification of the stele under drought. Root anatomical and architectural responses to drought are complex and vary among cultivars and root classes, and along root axes. Drought-induced proliferation of lateral roots on apical segments of axial roots would be expected to enhance deep water acquisition, while lignification of axial roots could help preserve axial water transport.

     

Proteomic analysis of rice leaves during drought stress and recovery

Three-week old plants of rice (Oryza sativa L. cv CT9993 and cv IR62266) developed gradual water stress over 23 days of transpiration without watering, during which period the mid-day leaf water potential declined to approximately -2.4 MPa, compared with approximately -1.0 MPa in well-watered controls. More than 1000 protein spots that were detected in leaf extracts by proteomic analysis showed reproducible abundance within replications. Of these proteins, 42 spots showed a significant change in abundance under stress, with 27 of them exhibiting a different response pattern in the two cultivars. However, only one protein (chloroplast Cu-Zn superoxide dismutase) changed significantly in opposite directions in the two cultivars in response to drought. The most common difference was for proteins to be up-regulated by drought in CT9993 and unaffected in IR62266; or down-regulated by drought in IR62266 and unaffected in CT9993. By 10 days after rewatering, all proteins had returned completely or largely to the abundance of the well-watered control. Mass spectrometry helped to identify 16 of the drought-responsive proteins, including an actin depolymerizing factor, which was one of three proteins detectable under stress in both cultivars but undetectable in well-watered plants or in plants 10 days after rewatering. The most abundant protein up-regulated by drought in CT9993 and IR62266 was identified only after cloning of the corresponding cDNA. It was found to be an S-like RNase homologue but it lacked the two active site histidines required for RNase activity. Four novel drought-responsive mechanisms were revealed by this work: up-regulation of S-like RNase homologue, actin depolymerizing factor and rubisco activase, and down-regulation of isoflavone reductase-like protein.