不同花生品种响应干旱胁迫后叶片内ABA与AhNCEDl的分布

以粤油7号和汕优523两个不同抗旱性品种为材料,研究响应干旱胁迫后叶片ABA（abscisicacid,脱落酸）和AhNCEDl（Arachishypogaeanine-cis-epoxycarotenoiddioxygenase）的分布以及含量变化。结果表明,两种花生品种响应干旱胁迫后叶片的维管组织中ABA分布增强且含量增加,AhNCEDl蛋白分布也增强;且在水分胁迫初期粤油7号花生AhNCEDl蛋白分布强于汕优523,其体内ABA分布水平也高于汕优523;经ABA生物合成抑制剂N印roxen处理后,两种花生叶片ABA分布减弱,但粤油7号叶片维管组织ABA分布水平仍高于汕优523。结果表明维管组织是干旱胁迫下花生叶片中ABA和AhNCEDl分布的主要区域,且粤油7号花生抗旱性强可能与其体内AhNCEDl和ABA的分布量较高有关。     

花生响应水分胁迫过程中叶片AhCYP707A1蛋白和ABA分布的变化

CYP707A蛋白是高等植物内源ABA代谢主要途径的关键酶,在水分胁迫过程中花生植株Ah CYP707A1蛋白和ABA分布与水平的变化并不清楚。研究结果表明,水分胁迫初期,花生叶片Ah CYP707A1蛋白表达均先被强烈抑制,促进ABA积累,随后蛋白表达回升,参与调节ABA稳态;叶片Ah CYP707A1蛋白以及ABA主要分布在叶片维管组织中。水分胁迫下,经CYP707A蛋白抑制剂处理后,花生叶片ABA分布和含量均有提高。抗旱花生品种‘粤油7’在水分胁迫下,Ah CYP707A1蛋白的表达以及分布均强于敏旱品种‘汕优523’,表明ABA代谢更为活跃。     

综合隶属函数法评价花生品种抗旱性与AhNCED1基因表达的关系

利用综合隶属函数法评价不同产地8个花生品种幼苗的抗旱能力, 同时分析各品种花生在模拟干旱处理2小时和12小时后叶片AhNCED1基因表达量的变化, 探讨花生品种抗旱性与叶片AhNCED1基因表达的关系, 建立花生(Arachis hypogaea)幼苗时期通过AhNCED1基因表达变化检测花生抗旱性等级的方法。结果显示, 干旱处理2小时, 各品种叶片AhNCED1基因表达量迅速增加, 与处理前相比差异极显著; 干旱处理12小时, 各品种花生叶片AhNCED1基因表达量均降低, 但仍均高于处理前水平。综合隶属函数值定量反映各品种抗旱性强弱顺序为: 花育24号>福花13号>粤油7号>中花15号>中花16号>航花2号>福花9号>北海1号。干旱处理2小时各品种花生叶片AhNCED1表达量变化大小依次为: 福花13号>花育24号>中花16号>中花15号>航花2号>粤油7号>北海1号>福花9号。其中, 抗旱性强的品种为花育24号和福花13号, 抗旱性弱的品种为福花9号和北海1号, 其余4个品种为中等抗旱。该抗旱性评价结果与这些品种在生产上的表现一致, 干旱胁迫2小时花生品种叶片AhNCED1基因的表达量变化与其抗旱性一致。因此, AhNCED1基因表达量可作为苗期花生品种抗旱性等级的量化指标之一。     

水分胁迫下花生叶片AhNCED1蛋白表达与气孔开度的变化

研究了水分胁迫下不同花生抗旱品种叶片气孔开度和相对含水量变化,分析TAhNCEDI基因和AhNCED1蛋白进行表达情况,发现水分胁迫下,叶片相对含水量下降,叶片气孔开度降低,叶片AhNCED1基因和AhNCED1蛋白表达增强。抗旱品种较之敏旱品种在响应水分胁迫初期时（1h）AhNCED1基因和AhNCED1蛋白表达较强,叶片气孔开度下降较快,引发气孔关闭,其叶片相对含水量较高,保水能力较强。ABA合成抑制剂naproxen处理后,叶片AhNCED1基因和AhNCED1蛋白的表达减弱,气孔开度快速增加,水分胁迫下花生叶片AhNCED1蛋白表达可能影响气孔开闭。     

非生物胁迫对花生叶片AhNCED1蛋白表达的影响

AhNCED1(9-cis-epoxycarotenoid dioxygenase 1 in Arachis hypogaea L.)是调控花生ABA(abscisic acid)生物合成的关键限速酶.利用Western blotting研究不同非生物胁迫对花生叶片AhNCED1蛋白表达的影响.结果表明渗透胁迫引起叶片AhNCED1蛋白表达快速(1 h)增加,ABA含量不断升高;NaCl处理后叶片AhNCED1蛋白在胁迫中期(7 h)表达增加,胁迫10 h时ABA含量显著升高;低温处理后叶片AhNCED1蛋白在胁迫后期(10 h)表达增加;高温胁迫后AhNCED1蛋白表达无明显变化.说明花生在感受(高渗、高盐、低温)等非生物胁迫后可能通过激活AhNCED1蛋白的表达,促使花生内源ABA水平升高以适应外界环境.     

AhNCED1基因转化花生研究

构建转化AhNCED1基因花生(Arachis hypogaea L.)过表达载体35S::AhNCED1::GUS,用OD600=0.8的LBA4404农杆菌液浸染汕油523,抗性芽诱导率达100%.PCR检测89株筛选苗,43株呈阳性,GUS检测阳性率为50%.转基因植株地上部分ABA含量增加;PEG胁迫10 h,转基因植株叶片AhNCEDl蛋白表达增强,内源ABA水平积累,超氧化物水平降低.     

脱水胁迫下抗旱性不同花生品种中某些生理生化指标变化比较

花生（Arachis hypogaea L．）品种‘粤油7’和‘汕油523’种子由广东省农业科学院作物研究所提供,前者抗旱性强,后者较弱。按Wan和Li（2005,2006）的方法对3叶期幼苗进行脱水胁迫处理0、1、2、4、8、10和24h后,取叶片用液氮速冻,于-80℃中冻存备用。每个处理重复3次。叶片失水率测定按王育红等（2002）的方法。根据刘宁等（2000）的方法测定叶片相对电导率。脯氨酸含量测定按张殿忠等（1990）的方法。内源脱落酸（ABA）按Xiong等（2001）的方法提取和纯化,以陈雪梅和王沙生（1992）的高效液相色谱法（HPLC）测定ABA。按Wan和Li（2006）的方法检测ABA生物合成关键酶基因AhNCED1的表达水平。得到如下结果：     

拟南芥干旱诱导型启动子RD29A驱动花生AhNCED1基因双元表达载体的构建

从拟南芥基因组中克隆RD29A基因5'-侧翼520bp启动子区域序列,生物信息学分析表明,该启动子片段中存在脱水胁迫响应元件(DRE)、ABA响应元件(ABRE)、TATA-box、CAAT-box等顺式作用元件。构建了干旱诱导型启动子AtRD29Ap驱动花生AhNCED1基因的植物双元表达载体pAtRD29Ap::AhNCED1。     

香蕉MaASRl基因的抗干旱作用

ASR（ABA,stress,ripening induced protein）是一类响应植物干旱胁迫的关键转录因子。在许多植物中已有报道,然而尚未见香蕉（Musa acuminata）VPASR与抗旱作用的相关研究。该实验从香蕉果实cDNA文库中筛选出1个AS尺基因,即MaASRl（登录号为AY628102）。干旱胁迫下,该基因在叶片中的表达量高于根部。将MaASRl转入拟南芥∽rabidopsisthaliana）,Southern检测确定了两株独立表达的转基因株系（命名为L14和L38）。表型观察发现,此两转基因株系的叶片变小且变厚Northern和Western检测结果表明,MaASR1在L14和L38中表达。控水处理后,L14和L38的存活率及脯氨酸含量均高于野生型。经干旱胁迫和外源ABA处理后,对MaASR1转基因株系中ABA／胁迫响应基因的表达分析,发现MaASR7可增强转基因株系对ABA信号的敏感度,但不能增强植株依赖于ABA途径的抗旱性。     

香蕉MaASR1基因的抗干旱作用

ASR(ABA, stress, ripening induced protein)是一类响应植物干旱胁迫的关键转录因子, 在许多植物中已有报道, 然而尚未见香蕉(Musa acuminata)中ASR与抗旱作用的相关研究。该实验从香蕉果实cDNA文库中筛选出1个ASR基因, 即MaASR1(登录号为AY628102)。干旱胁迫下, 该基因在叶片中的表达量高于根部。将MaASR1转入拟南芥(Arabidopsis thaliana), Southern检测确定了两株独立表达的转基因株系(命名为L14和L38)。表型观察发现, 此两转基因株系的叶片变小且变厚; Northern和Western检测结果表明, MaASR1在L14和L38中表达。控水处理后, L14和L38的存活率及脯氨酸含量均高于野生型。经干旱胁迫和外源ABA处理后, 对MaASR1转基因株系中ABA/胁迫响应基因的表达分析, 发现MaASR1可增强转基因株系对ABA信号的敏感度, 但不能增强植株依赖于ABA途径的抗旱性。     

Recurrent Mild Drought Events Increase Resistance Toward Extreme Drought Stress

The frequency and magnitude of extreme weather events such as drought are expected to increase in the future. At present, plant responses to recurrent extreme events have been sparsely examined and the role of stress history on subsequent stress response has been widely neglected. In a long-term field experiment, we investigated the response of grassland and heath communities to a very severe drought event, which exceeded the duration of projected drought scenarios. During the preceding 6 years, the plant communities experienced scenarios of varying water supply, including annually recurring drought, heavy rain, regular watering, and natural drought periods. Single species and plant communities that were regularly watered in the preceding years revealed the highest tissue die-back under a very severe drought when compared to plants that experienced mild or severe drought stress before. Contrary to expectations, the root to shoot ratio did not increase due to previous recurrent drought occurrences. Furthermore, pre-exposure effects on Vaccinium myrtillus and Plantago lanceolata tissue die-back and reproductive biomass (P. lanceolata) were altered by community composition. Recurrent mild drought stress seems to improve drought resistance of plant communities and species. Potential reasons could be epigenetic changes or soil biotic legacies. Morphological legacies such as altered root to shoot ratio did not play a role in our study. Imprinting events which trigger this ecological stress memory do not have to be extreme themselves. Thresholds, longevity of effects, and the role of biodiversity shown by the importance of community composition require further attention.     

Drought and drought tolerance

Drought tolerance is a nebulous term that becomes more nebulous the more closely we look at it, much as a newspaper photograph does when viewed through a magnifying glass. From the vantage point of an ecologist the features that distinguish xerophytic from mesophytic vegetation are clear. We can all tell that a cactus is more drought tolerant than a carnation. But when we look at crop plants, the features that confer drought tolerance are far from clear. The main reason for the contrast is that the traits we associate with xerophytes typically concern survival during drought, whereas with crops we are concerned with production—and insofar as the term drought tolerance has any useful meaning in an agricultural context, it must be defined in terms of yield in relation to a limiting water supply.Further, with the well-developed major crop plants, those of us trying to increase water-limited yield would be pleased to achieve improvements of just a few percent in environments that are highly variable in their water supply. This variability often means that several seasons are required to demonstrate the advantages of an allegedly improved cultivar. Traits that confer drought tolerance in such circumstances are subtle, and may manifest themselves in some types of drought but not in others. Indeed the most influential characters often have no direct connection to plant water relations at all, as I elaborate on below.I will concentrate on the agricultural rather than the natural environment (although there are no doubt lessons for us still to learn from analysing the behaviour of natural vegetation—see Monneveux, this volume), and will argue that drought tolerance is best viewed at an ontogenetic time scale—i.e. at the time scale of the development of the crop—weeks to months for an annual crop. The timing of the main developmental changes, like floral initiation and flowering, and the rate of development of leaf area in relation to the seasonal water supply, are the most important variables at this time scale. Occasionally though, rapid changes in the environment, such as a sudden large rise in air temperature and humidity deficit, perhaps associated with hot dry winds, make appropriate short-term physiological and biochemical responses essential for the survival of the crop. These short term responses may be amenable to cellular and sub-cellular manipulation, especially if the sudden environmental deterioration occurs at especially sensitive stages in development such as pollen meiosis or anthesis.Purists insist that drought is a meteorological term that refers only substantial to periods in which rainfall fails to keep up with potential evaporation. Within the spirit of this meeting it is appropriate to interpret the term more loosely than this definition, and to define it as circumstances in which plants suffer reduced growth or yield because of insufficient water supply, or because of too large a humidity deficit despite there being seemingly adequate water in the soil.     

Drought avoidance byCyperus rotundus

Cyperus rotundus L. is a hygrophilous plant, but it flourishes well even in the Indian desert. Higher bound water, hygroscopic capacity, % dry matter, lower desiccation rate and volume to mass ratio, development of thick sclerenchymatous layer, presence of cortical vascular bundles and endodermis-like layer appear to be the factors responsible for such adaptation.     

Drought response of two bedding plants

Bedding plants are an important part of the urban public space and private gardens. However, they are not always properly watered and suffer from drought stress, especially when grown in containers. In this trial a response to water stress of two commonly used species, impatiens (Impatiens walleriana Hook) and geranium (Pelargonium hortorum L. H. Bailey) were compared. The former is highly herbaceous and prone to wilting whereas the latter has hairy leaves and is better adapted to drought. Plants were grown at three levels of soil water content (SWC): 80% (control), 60% (mild stress) and 30% (severe stress). Drought was maintained during three 10 day cycles, separated by 10 day periods of normal watering. In both species roots were significantly longer in plants grown at 30% SWC as compared to 80% SWC while plant height and flower number were reduced by drought only in impatiens. The initial relative water content (RWC) was lower in geranium and decreased less in response to drought than in impatiens. Ammonium content in leaves of both species increased significantly under stress but the ranges of increase were different in both species. There was a significant increase in the free amino acids content in leaves of impatiens as compared to geranium but this rise was more time than drought dependent. The reduction in the a + b chlorophyll concentration in leaves of impatiens was significantly time and stress dependent while no reaction in geranium was observed. The above results show that changes in leaf RWC merit further attention as a possible indicator of plant response to drought stress in ornamental plants but additional studies are needed before this or other parameters can be used to evaluate new bedding plants for introduction into urban growing conditions, or as selection criteria in breeding for adaptation to demanding growing conditions.     

Drought and dieback of rural eucalypts

The possibility that drought causes dieback of eucalypts in rural Australia was investigated. Water potential and canopy condition in dieback and healthy rural Eucalyptus blakelyi and E. melliodora trees were compared during and after an extreme drought in the ACT. All the trees were drought affected, but the extent was independent of the condition of their canopies at the beginning of the study.     

翅果油树幼苗抗旱性

通过盆栽试验,研究不同土壤水分条件下翅果油树（Elaeagnus mollis）幼苗的生长、叶水分和丙二醛含量等各项生理指标的变化。结果表明,轻、中度干旱（30％～35％、45％～50％）胁迫时叶片含水量和叶绿素含量下降幅度较小,水势较高,丙二醛含量较低,翅果油树幼苗能保汪基本的生长,表现出耐旱植物的生理特征;在重度干旱胁迫（20％～25％）条件下,叶含水量和叶绿素含量下降较显著,水势最低,丙二醛含量最高,植株矮小,颜色发黄,表明翅果油树幼苗受到干旱伤害严重,不能正常生长。     

六种园林植物耐旱性分析

为选择耐旱性较强的园林绿化植物,选择6种常见的园林植物：金银木（Lonicera maackii）、紫荆（Cercis chinensis）、紫薇（Lagerstroemia indica）、荆条（Vitex negundo var.heterophylla）、胡枝子（Lespedeza bicolor）和构树（Broussonetia papyrifera）,进行盆栽控水试验,对植株外观形态和土壤含水率、叶片叶绿素含量、超氧化物歧化酶（SOD）活性、丙二醛（MDA）含量进行比较。结果表明,随干旱胁迫时间的延长,土壤含水量均呈下降趋势,金银木、胡枝子和荆条的长势较好;紫薇、紫荆和构树出现叶片萎蔫、掉落现象,6种植物叶片的光合色素含量呈先上升后下降的趋势,除紫薇外,SOD活性总体均呈上升趋势,MDA含量持续上升。可见,金银木、胡枝子和荆条的耐旱性较强,紫薇、紫荆和构树的耐旱性较弱。     

Advances in Drought Resistance of Rice

Water deficit is a serious environmental stress and the major constraint to rice productivity. Losses in rice yield due to water shortage probably exceed losses from all other causes combined and the extent of the yield loss depends on both the severity and duration of the water stress. Drought affects rice at morphological, physiological, and molecular levels such as delayed flowering, reduced dry matter accumulation and partitioning, and decreased photosynthetic capacity as a result of stomatal closure, metabolic limitations, and oxidative damage to chloroplasts. Small-statured rice plants with reduced leaf area and short growth duration are better able to tolerate drought stress, although the mechanisms are not yet fully understood. Increased water uptake by developing larger and deeper root systems, and the accumulation of osmolytes and osmoprotectants are other important mechanisms for drought resistance. Drought resistance in rice has been improved by using plant growth regulators and osmoprotectants. In addition, several enzymes have been found that act as antioxidants. Silicon has also improved drought resistance in rice by silicification of the root endodermis and improving water uptake. Seed priming improves germination and crop stand establishment under drought. Rice plants expressing HVA1, LEA proteins, MAP kinase, DREB and endo-1, 3-glucanase are better able to withstand drought stress. Polyamines and several enzymes act as antioxidants and reduce adverse effects of drought stress in rice. Drought resistance can be managed by developing and selecting drought-tolerant genotypes. Rice breeding and screening may be based on growth duration, root system, photosynthesis traits, stomatal frequency, specific leaf weight, leaf water potential, and yield in target environments. This review discusses recent developments in integrated approaches, such as genetics, breeding and resource management to increase rice yield and reduce water demand for rice production.     

Separating Drought Effects from Roof Artifacts on Ecosystem Processes in a Grassland Drought Experiment

1

Given the predictions of increased drought probabilities under various climate change scenarios, there have been numerous experimental field studies simulating drought using transparent roofs in different ecosystems and regions. Such roofs may, however, have unknown side effects, called artifacts, on the measured variables potentially confounding the experimental results. A roofed control allows the quantification of potential artifacts, which is lacking in most experiments.

2

We conducted a drought experiment in experimental grasslands to study artifacts of transparent roofs and the resulting effects of artifacts on ecosystems relative to drought on three response variables (aboveground biomass, litter decomposition and plant metabolite profiles). We established three drought treatments, using (1) transparent roofs to exclude rainfall, (2) an unroofed control treatment receiving natural rainfall and (3) a roofed control, nested in the drought treatment but with rain water reapplied according to ambient conditions.

3

Roofs had a slight impact on air (+0.14°C during night) and soil temperatures (−0.45°C on warm days, +0.25°C on cold nights), while photosynthetically active radiation was decreased significantly (−16%). Aboveground plant community biomass was reduced in the drought treatment (−41%), but there was no significant difference between the roofed and unroofed control, i.e., there were no measurable roof artifact effects.

4

Compared to the unroofed control, litter decomposition was decreased significantly both in the drought treatment (−26%) and in the roofed control treatment (−18%), suggesting artifact effects of the transparent roofs. Moreover, aboveground metabolite profiles in the model plant species Medicago x varia were different from the unroofed control in both the drought and roofed control treatments, and roof artifact effects were of comparable magnitude as drought effects.

5

Our results stress the need for roofed control treatments when using transparent roofs for studying drought effects, because roofs can cause significant side effects.