Terminal drought and seed priming improves drought tolerance in wheat

Plants retain the preceding abiotic stress memory that may aid in attainment of tolerance to subsequent stresses. This study was conducted to evaluate the influence of terminal drought memory (drought priming) and seed priming in improving drought tolerance in wheat (Triticum aestivum L.). During first growing season, wheat was planted in field under optimal (well-watered) and drought stress imposed at reproductive stage (BBCH growth stage 49) until maturity (BBCH growth stage 83). Seeds collected from both sources were subjected to hydropriming or osmopriming (with 1.5% CaCl₂ solution); while, dry seed was taken as control. Treated and control seeds, from both sources, were sown in soil filled pots. After the completion of seedling emergence, pots were maintained at 50% water holding capacity (drought) or 100% water holding capacity (well-watered). Drought stress suppressed the plant growth (2–44%), perturbed water relations (1–18%) and reduced yield (192%); however, osmolytes accumulation (3–14%) and malondialdehyde contents (26–29%) were increased under drought. The crop raised from the seeds collected from terminal drought stressed plants had better growth (5–63%), improved osmolyte accumulation (13–45%), and lower lipid peroxidation (3%) than the progeny of well-watered crop. Seed priming significantly improved the crop performance under drought stress as compared to control. However, osmopriming was more effective than hydropriming in this regard as it improved leaf area (9–43%), tissue water status (2–47%), osmolytes accumulation (6–48%) and grain yield (14–79%). In conclusion, terminal drought induced modifications in seed composition and seed priming improved transgenerational drought tolerance through improvement in tissue water status and osmolytes accumulation, and decrease in lipid peroxidation.     

Genetic basis of drought resistance at reproductive stage in rice: separation of drought tolerance from drought avoidance

Drought tolerance (DT) and drought avoidance (DA) are two major mechanisms in drought resistance of higher plants. In this study, the genetic bases of DT and DA at reproductive stage in rice were analyzed using a recombinant inbred line population from a cross between an indica lowland and a tropical japonica upland cultivar. The plants were grown individually in PVC pipes and two cycles of drought stress were applied to individual plants with unstressed plants as the control. A total of 21 traits measuring fitness, yield, and the root system were investigated. Little correlation of relative yield traits with potential yield, plant size, and root traits was detected, suggesting that DT and DA were well separated in the experiment. A genetic linkage map consisting of 245 SSR markers was constructed for mapping QTL for these traits. A total of 27 QTL were resolved for 7 traits of relative performance of fitness and yield, 36 QTL for 5 root traits under control, and 38 for 7 root traits under drought stress conditions, suggesting the complexity of the genetic bases of both DT and DA. Only a small portion of QTL for fitness- and yield-related traits overlapped with QTL for root traits, indicating that DT and DA had distinct genetic bases.     

花生幼苗对重复干旱胁迫的生理响应

防雨棚内设盆栽试验,设置对照(Control,75%田间持水量)、干旱胁迫(D,35%)、重复干旱胁迫(D_D,35%)3个处理,探讨花生幼苗对预干旱胁迫的适应和记忆响应,分析预干旱对缓解重复干旱胁迫危害的生理作用。结果表明,与干旱胁迫处理相比,重复干旱胁迫提高了叶片的相对含水量,减少脯氨酸的积累,降低MDA和O·_2~-含量;抗氧化酶SOD、CAT活性降低,其中POD活性降低最为明显,并在复水后恢复到与对照相同水平或低于对照。与正常水分的对照相比,干旱胁迫显著降低叶片光合速率(P_N)、最大光合势能(P_C)、最大光量子产量(Y_Q),但重复干旱处理在重复干旱胁迫时期和复水后P_N、P_C和Y_Q均高于干旱处理。预干旱胁迫导致光合和气孔导度滞后面积、滞后率(H_P和H_g)增加,经过预干旱胁迫后,重复干旱显著降低光合和气孔导度滞后面积和滞后率。预干旱胁迫提高植株在重复干旱胁迫下叶片含水量,减轻重复干旱对植株造成的生理伤害,在光合作用上提高对重复干旱的抵御能力,并在复水后快速恢复到正常水分条件下植株生长水平,减少干旱对植株的不利影响。因此,预干旱胁迫促使花生幼苗具备适应或可记忆初始胁迫的能力,重复干旱胁迫时表现更为迅速和强烈的生理防御和快速的生理恢复机制。     

Signalling drought in guard cells

A number of environmental conditions including drought, low humidity, cold and salinity subject plants to osmotic stress. A rapid plant response to such stress conditions is stomatal closure to reduce water loss from plants. From an external stress signal to stomatal closure, many molecular components constitute a signal transduction network that couples the stimulus to the response. Numerous studies have been directed to resolving the framework and molecular details of stress signalling pathways in plants. In guard cells, studies focus on the regulation of ion channels by abscisic acid (ABA), a chemical messenger for osmotic stress. Calcium, protein kinases and phosphatases, and membrane trafficking components have been shown to play a role in ABA signalling process in guard cells. Studies also implicate ABA-independent regulation of ion channels by osmotic stress. In particular, a direct osmosensing pathway for ion channel regulation in guard cells has been identified. These pathways form a complex signalling web that monitors water status in the environment and initiates responses in stomatal movements.     

Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

Forest biogeochemistry in response to drought

Trees alter their use and allocation of nutrients in response to drought, and changes in soil nutrient cycling and trace gas flux (N₂O and CH₄) are observed when experimental drought is imposed on forests. In extreme droughts, trees are increasingly susceptible to attack by pests and pathogens, which can lead to major changes in nutrient flux to the soil. Extreme droughts often lead to more common and more intense forest fires, causing dramatic changes in the nutrient storage and loss from forest ecosystems. Changes in the future manifestation of drought will affect carbon uptake and storage in forests, leading to feedbacks to the Earth's climate system. We must improve the recognition of drought in nature, our ability to manage our forests in the face of drought, and the parameterization of drought in earth system models for improved predictions of carbon uptake and storage in the world's forests.     

Morpho-physiological and molecular characterization of drought tolerance traits in Gossypium hirsutum genotypes under drought stress

Drought stress is one of the major abiotic stresses affecting lint yield and fibre quality in cotton. With increase in population, degrading natural resources and frequent drought occurrences, development of high yielding, drought tolerant cotton cultivars is critical for sustainable cotton production across countries. Six Gossypium hirsutum genotypes identified for drought tolerance, wider adaptability and better fibre quality traits were characterized for various morpho-physiological and biochemical characters and their molecular basis was investigated under drought stress. Under drought conditions, genotypes revealed statistically significant differences for all the morpho-physiological and biochemical traits. The interaction (genotype × treatment) effects were highly significant for root length, excised leaf water loss and cell membrane thermostability indicating differential interaction of genotypes under control and stress conditions. Correlation studies revealed that under drought stress, relative water content had significant positive correlation with root length and root-to-shoot ratio while it had significant negative correlation with excised leaf water loss, epicuticular wax, proline, potassium and total soluble sugar content. Analysis of expression of fourteen drought stress related genes under water stress indicated that both ABA dependent and ABA independent mechanisms of drought tolerance might be operating differentially in the studied genotypes. IC325280 and LRA5166 exhibited ABA mediated expression of stress responsive genes and traits. Molecular basis of drought tolerance in IC357406, Suraj, IC259637 and CNH 28I genotypes could be attributed to ABA independent pathway. Based on physiological phenotyping, the genotypes IC325280 and IC357406 were identified to possess better root traits and LRA5166 was found to have enhanced cellular level tolerance. Variety Suraj exhibited good osmotic adjustment and better root traits to withstand water stress. The identified drought component trait(s) in specific genotypes would pave way for their pyramiding through marker assisted cotton breeding.Electronic supplementary materialThe online version of this article (10.1007/s12298-020-00890-3) contains supplementary material, which is available to authorized users.     

基于温度植被干旱指数的土库曼斯坦典型绿洲干旱遥感监测

针对目前中亚地区广泛存在的农业干旱问题,选取土库曼斯坦典型绿洲为研究区,利用2幅MODIS影像和同期过境的Landsat影像,获取归一化植被指数(NDVI)和地表温度(Ts),构建NDVI-Ts特征空间,计算得到2001和2011年2种温度植被干旱指数TVDITM和TVDIMODIS.利用较高分辨率的Landsat TM数据对MODIS数据反演结果进行验证.结果表明:2001年、2011年TVDITM和TVDIMODIS的绝对误差分别为0.0178和0.0228;均方根误差分别为0.0226和0.0279;相关系数分别为0.949和0.922,说明TVDI可有效反映区域土壤干旱情况.研究区内干旱区域占总面积的60％以上,旱情由绿洲中心向外围逐步严重.近10年来,研究区内土壤湿度低值区呈现扩大趋势,湿润和正常所占比例下降了5.32％,干旱和重旱的比例上升了14％,旱情情况总体加剧.因此,利用MODIS影像的温度植被旱情指数可有效地监测中亚地区干旱情况.     

5种干旱指数在吉林省农业干旱评估中的适用性

干旱是对吉林省农业生产影响最大的气象灾害,干旱指数能够表征农业旱情,但不存在普遍适用的干旱指数,开展干旱指数在吉林省农业干旱评估中的适用性研究具有重要的现实意义.基于1961-2014年吉林省的逐日气象数据、土壤水分资料和历史旱情统计信息,选取典型干旱年和典型干旱区,评估了降水量距平百分率(PA)、相对湿润度指数(MI)、作物水分亏缺距平指数(CWDIa)、帕默尔干旱指数(PDSI)和气象干旱综合指数(MCI)共5种干旱指数在吉林省农业干旱评估中的适用性.结果表明:对于1997和2007年两个典型旱年,MI对农业旱情的评价结果与旱情记录较一致,PA和MCI次之.对于吉林省典型旱区(西部通榆、中部梨树、东部和龙),MI和PDSI对农业旱情的评估较好.在农作物生长季,PA较适用于评价4、7和8月的旱情,MI较适用于评价4、5和9月的旱情,CWDIa只适用于评价5月的旱情,PDSI对6-9月的旱情均有一定的指示作用,MCI适用于5-8月的农业干旱过程评估.从农业干旱发生范围来看,MI、PDSI和MCI较适用于评估吉林省西部旱情,PDSI较适用于评价吉林省中部旱情,PA、PDSI和MCI较适用于评估吉林省东部旱情.     

Leaf optical properties during and after drought stress in triticale and maize genotypes differing in drought tolerance

The effect of a short (7 days) and prolonged (14 days) soil drought (D) on leaf optical properties (R reflectance, T transmittance and A absorbance) in PAR and NIR range of irradiation, and on changes in leaf water potential (ψ), leaf injury index (LI), leaf thickness (LT) and chlorophyll (a + b) content (Chl) was studied for maize and triticale genotypes differing in drought tolerance. Under control conditions (C) leaves of maize in comparison to triticale were better hydrated, were thicker and had higher content of chlorophyll (a + b). In non-stressed plants, small differences were observed in measurements of R, T and A. In the range from 500 to 600 nm, the differences between D-resistant and D-sensitive were observed only in transmittance (T) and in range from 700 to 1,100 nm in absorbance (A). In genotypes belonging to the group of D-sensitive T in PAR range and A in NIR range were two times higher than in D-resistant ones. However, in NIR range R for D-sensitive genotypes was lower than for D-resistant ones. The drought stress caused the decrease in ψ, Chl, LT and the increase in leaf injury index (LI). Soil drought applied within 14 days caused larger changes in these physiological characters in comparison to 7 days drought. The observed harmful influence of drought was more visible for maize than triticale. Moreover for genotypes belonging to D-sensitive ones, changes were larger than for D-resistant ones. Similar to changes in ψ, LT and LI drought stress caused changes in leaf optical properties parameters R, A and T. In the PAR range, the highest changes were observed in R, whereas changes in T and A, which were not considerable. Both in maize and triticale, increase in R was higher in plants subjected to 14 days drought than in plants exposed to drought for 7 days. In maize, increase in R was larger for D-sensitive genotype. For both species, changes in T and A of PAR range were small. In NIR range, an increase in R and A, and decrease in T were observed. After 7 days of recovery in plants subjected to shorter period of drought significant differences were still visible in most cases. The same was observed for ψ, LT, LI and Chl parameters. It shows that the period of 7 days rehydration is too short to remove the injuries caused by drought stress. This results indicate that measurements of R, T and A might be useful in practical application for the estimation of the drought tolerance level. Some limitations in the practical application for plant breeding may be caused by relatively high cost of necessary equipment.     

Recent increases in drought frequency cause observed multi-year drought legacies in the tree rings of semi-arid forests

Oecologia - Recent analyses on the length of drought recovery in forests have shown multi-year legacies, particularly in semi-arid, coniferous ecosystems. Such legacies are usually attributed to...     

Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato

Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However, the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated with the host plant–AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non‐AM and AM plants. Three different water regimes were applied, and their effects were analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non‐AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non‐AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions, plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.     

基于优选遥感干旱指数的华北平原干旱时空变化特征分析

基于中分辨率成像光谱仪(MODIS)产品和气象资料,对比分析了作物缺水指数(CWSI)、干旱严重度指数(DSI)、归一化植被供水指数(NVSWI)和温度植被干旱指数(TVDI)表征华北平原干旱状况的适用性,并基于优选后的指数研究了2000—2018年干旱的时空变化特征。结果表明：(1)CWSI在反映干旱的效果上明显优于另外三种干旱指数。(2)时间上,2000—2018年春季干旱最严重,其次是秋季和冬季,夏季干旱最轻,但春季干旱强度有所下降,速率为-0.03/10a,而其他三季均呈增加趋势,速率为(0.01—0.08)/10a。(3)空间上,华北平原东部和东南部发生轻旱频率高,西部和北部中旱及以上干旱频率较高。山东省西北部及河南省东部、安徽省北部等地春旱呈显著减弱趋势(P<0.05);夏季华北平原东南部干旱增加趋势显著(P<0.05),而北部减弱趋势显著(P<0.05);秋季华北平原西南一带干旱上升趋势较大;冬季西部、中部及南部干旱增加趋势显著(P<0.05)。     

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.     

A drought rarity and evapotranspiration-based index as a suitable agricultural drought indicator

Agricultural drought has a substantial impact on crop yields and, thus, food security within the context of global climate change. Therefore, efforts should focus on agricultural drought detection and monitoring. Agricultural drought is identified as unusually dry conditions in which severe water stress impedes crop growth. Thus, the crop water deficit severity and rarity are both key factors in agricultural drought detection and are rarely considered simultaneously in existing drought indices. To overcome this limitation, an integrated agricultural drought index (IADI) based on drought rarity and evapotranspiration is proposed. As an important grain production base, Northeast China has suffered from frequent droughts in recent years, demonstrating an urgent need for accurate drought monitoring. In this study, the superiority of the IADI as an agricultural drought indicator through the detection of the severity and rarity was tested using the drought disaster area (DDA) and grain yield, and its performance was compared to that of the evaporative drought index (EDI), an indicator that accounts for only the water deficit severity. The response of agricultural drought to meteorological drought and its impact on the grain yield were further analyzed. The results showed that (1) the IADI can effectively capture the drought variability and identify drought events by combining the detection of the severity and rarity. (2) The R² value between the DDA and IADI (0.72) was higher than that with the EDI (0.50), and the same result was found in a comparative analysis using the grain yield, showing that the IADI is a suitable indicator for agricultural drought assessment. (3) Severe and extreme meteorological droughts and extreme agricultural droughts in western Jilin and western Liaoning were more frequent than in other regions, highlighting the agricultural drought tendency and sensitivity to precipitation deficit in this region. (4) The impacts of agricultural drought on grain yield in three provinces of Northeast China vary greatly during the crop-growing period, with the most significant impacts occurring from May to July. Therefore, this period represents the critical crop water requirement period, and timely irrigation should be ensured during this period.