Impact of drought stress on growth and quality of miscanthus for biofuel production

Miscanthus has a high potential as a biomass feedstock for biofuel production. Drought tolerance is an important breeding goal in miscanthus as water deficit is a common abiotic stress and crop irrigation is in most cases uneconomical. Drought may not only severely reduce biomass yields, but also affect biomass quality for biofuel production as cell wall remodeling is a common plant response to abiotic stresses. The quality and plant weight of 50 diverse miscanthus genotypes were evaluated under control and drought conditions (28 days no water) in a glasshouse experiment. Overall, drought treatment decreased plant weight by 45%. Drought tolerance – as defined by maintenance of plant weight – varied extensively among the tested miscanthus genotypes and ranged from 30% to 110%. Biomass composition was drastically altered due to drought stress, with large reductions in cell wall and cellulose content and a substantial increase in hemicellulosic polysaccharides. Stress had only a small effect on lignin content. Cell wall structural rigidity was also affected by drought conditions; substantially higher cellulose conversion rates were observed upon enzymatic saccharification of drought‐treated samples with respect to controls. Both cell wall composition and the extent of cell wall plasticity under drought varied extensively among all genotypes, but only weak correlations were found with the level of drought tolerance, suggesting their independent genetic control. High drought tolerance and biomass quality can thus potentially be advanced simultaneously. The extensive genotypic variation found for most traits in the evaluated miscanthus germplasm provides ample scope for breeding of drought‐tolerant varieties that are able to produce substantial yields of high‐quality biomass under water deficit conditions. The higher degradability of drought‐treated samples makes miscanthus an interesting crop for the production of second‐generation biofuels in marginal soils.     

抗旱相关基因在烟草中的应用研究进展

干旱是影响烟草正常生长、发育、产量和烟叶品质的一个重要逆境因子。在干旱胁迫下,植物体内会通过激发一些抗旱基因的表达来增强植物的抗旱能力。目前,很多抗旱相关的功能蛋白基因和调控蛋白基因已被克隆并在烟草中实现了遗传转化,外源抗旱基因的表达提高了转基因烟草的抗旱能力。抗旱基因的克隆为烟草抗旱新品种的培育奠定了良好的分子基础,系统深入地研究抗旱相关基因在干旱胁迫条件下的表达与调控,可为通过基因工程手段提高烟草的抗旱能力开辟新途径,同时也能为其他农作物的抗旱分子育种和品种改良提供基因资源。     

Identification of RAPD and ISSR markers for drought tolerance in wheat (Triticum aestivum L.)

Drought tolerance is the essential trait that needs to be incorporated in cereal crops, particularly those grown under the rainfed cultivation. Drought tolerance being contributed by several regions of the genome requires identification of these regions, using suitable molecular markers. Therefore, present investigation was aimed at analyzing the genetic diversity present among the cultivars of rainfed and the irrigated areas with respect to the drought tolerant trait. In all, 14 RAPD and 90 ISSR markers were used to identify these genomic regions. Out of 14 RAPD markers, one RAPD primer exhibited polymorphic banding pattern with 18.6 % polymorphism, clearly separating drought tolerant and drought susceptible genotypes. Out of 90 ISSR primers, only 3 ISSR primers revealed polymorphism in relation to the drought tolerance trait exhibiting 21.38 % polymorphism.     

干旱对陆地生态系统生产力的影响

该文综述了干旱对陆地生态系统生产力的影响,分析了其影响机制,并总结了植被对干旱的响应与适应及其机理机制。干旱通过抑制光合作用来降低陆地生态系统总初级生产力,干旱还可以降低生态系统的自养呼吸和异养呼吸。同时干旱还可以通过影响其它干扰形式来间接影响陆地生态系统生产力,如增加火干扰的发生频率和强度,增加植物的死亡率,增加病虫害的发生等。在生态系统水平上干旱可以降低碳固定,减弱碳汇功能,甚至把生态系统从碳汇改变成碳源。目前生态系统水平上的干旱影响研究主要通过两种方法实现,一种是模型模拟,另一种就是大型模拟实验。作为陆地生态系统生产力的实现者,在干旱胁迫条件下,植物也会采取积极的适应策略以减弱干旱对生态系统生产力的影响,其适应策略主要分以下3种:在一些周期性发生干旱的地区,植物会调整生长期以避开干旱或通过休眠来减弱干旱所造成的伤害;还有一些植物会通过调节体内的代谢过程,改变一些生理特性来抵御干旱;而长期生活在干旱条件下的植物则通过进化来改变了自身的生理生化代谢过程,形成耐旱机制。目前,植物对干旱响应的分子学机制,以及生态系统水平上对干旱的响应和适应仍然是薄弱的领域,也必然成为未来研究的重点。     

Challenges in pea breeding for tolerance to drought: Status and prospects

Drought is increasingly frequent in the context of climate change and is considered a major constraint for crop yield. Water scarcity can impair growth, disturb plant water relations and reduce water use efficiency. Pea (Pisum sativum) is a temperate grain legume rich in protein, fibre, micronutrients and bioactive compounds that can benefit human health. In reducing pea yield because of drought, the intensity and duration of stress are critical. This review describes several drought resistance mechanisms in pea based on morphology, physiology and biochemical changes during/after the water deficit period. Drought tolerance of pea can be managed by adopting strategies such as screening, breeding and marker-assisted selection. Therefore, various biotechnological approaches have led to the development of drought-tolerant pea cultivars. Finally, the main objective of the current research is to point out some useful traits for drought tolerance in peas and also, mention the methods that can be useful for future studies and breeding programmes.     

Physiological and biochemical adaptations in lentil genotypes under drought stress

Drought is a major restrictive factor for declining grain yield in lentil globally. Present investigation was conducted by taking microsperma (HUL-57) and macrosperma (IPL-406) genotypes of lentil (Lens culinaris Medik.) as information regarding physiological and biochemical basis of differences in drought resistance in macrosperma (bold-seeded) and microsperma (small-seeded) are not well understood. Pot grown plants were exposed to drought stress at specific phenophase viz. mid-vegetative, flower initiation and pod formation stage by withholding irrigation till the plants experienced one cycle of permanent wilting (PWP). Genotypes exhibited substantial differences for most of the measured traits under drought irrespective of the phenophase of stress imposed. Under drought HUL-57 had lower CMI, higher CSI, lower values of Δ¹³C, maintained higher SLN, accumulated more N and efficiently remobilized accumulated N to developing seeds. Higher chlorophyll content, increased accumulation of osmotically active solutes viz. soluble sugars and proline under drought stress was evident in HUL-57. Drought induced H₂O₂ accumulation and lipid peroxidation in both genotypes, but increments were of lesser magnitudes in HUL-57. Drought stress of pod formation stage followed by flower initiation stage was most damaging than the stress imposed at mid-vegetative stage in both genotypes. HUL-57 showed a better drought resistance capacity than IPL-406. Drought indices viz. DSI, STI and MP are proposed as criterion to identify and breed lentil genotypes for drought conditions.     

Functional traits predict drought performance and distribution of Mediterranean woody species

Water availability is one of the key environmental factors that affect plant establishment and distribution. In many regions water availability will decline with climate change, exposing small seedlings to a greater likelihood of drought. In this study, 17 leaves, stem, root, and whole-plant traits of ten woody Mediterranean species were measured under favourable growing conditions and seedling drought survival was evaluated during a simulated dry-down episode. The aims of this study were: i) to assess drought survival of different species, ii) to analyse which functional traits predict drought survival time, and iii) to explain species distribution in the field, based on species drought survival and drought strategies. Drought survival time varied ten-fold across species, from 19 to 192 days. Across species, drought survival was positively related to the rooting depth per leaf area, i.e., the ability to acquire water from deeper soil layers while reducing transpiring leaf area. Drought survival time was negatively related to species ability to grow quickly, as indicated by high relative growth and net assimilation rates. Drought survival also explained species distribution in the field. It was found that species were sorted along a continuum, ranging between two contrasting species functional extremes based on functional traits and drought performance. One extreme consisted of acquisitive fast-growing deciduous species, with thin, soft metabolically active leaves, with high resource use and vulnerability to drought. The opposite extreme consisted of conservative slow-growing evergreen species with sclerophyllous leaves, deep roots, a low transpiring area, and low water use, resulting in high drought survival and drought tolerance. The results show that these drought strategies shape species distribution in this Mediterranean area.     

Interaction between PGPR and PGR for water conservation and plant growth attributes under drought condition

Drought is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Drought stress accompanied by reduction in precipitation pose major challenges to future food safety. Strategies should be develop to enhance drought tolerance in crops like chickpea and wheat, in order to enhance their growth and yield. Drought tolerance strategies are costly and time consuming however, recent studies specify that plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can help plants to withstand under harsh environmental condition and enable plants to cope with drought stress. PGPR can act as biofertilizer and bioenhancer for different legumes and non-legumes. The use of PGPR and symbiotic microorganisms, may be valuable in developing strategies to assist water conservation in plants. The use of PGPR has been confirmed to be an ecologically sound way of enhancing crop yields by facilitating plant growth through direct or indirect mechanism. The mechanisms of PGPR for water conservation include secretion of exopolysaccharides, biofilm formation, alternation in phytohormone content, improvement in sugar concentration, enhancing availability of micro- and macronutrients and changes in plant functional traits. Similarly, plant growth regulators (PGRs) are specially noticed in actively growing tissues under stress conditions and have been associated in the control of cell division, embryogenesis, root formation, fruit development and ripening, and reactions to biotic and abiotic stresses and upholding water conservation status in plants. Previous studies also suggest that plant metabolites interact with plant physiology under stress condition and impart drought tolerance. Metabolites like, sugars, amino acids, organic acid and polyols play a key role in drought tolerance of crop plants grown under stress condition. It is concluded from the present study that PGRs in combination with PGPR consortium can be an effective formulation to promote plant growth and maintenance of plant turgidity under drought stress. This review is a compilation of the effect of drought stress on crop plants and described interactions between PGPR/PGRs and plant development, knowledge of water conservation and stress release strategies of PGPR and PGRs and the role of plant metabolites in drought tolerance of crop plants. This review also bridges the gaps that summarizes the mechanism of action of PGPR for drought tolerance of crop plants and sustainability of agriculture and applicability of these beneficial rhizobacteria in different agro-ecosystems under drought stress.     

Drought induced programmed cell death and associated changes in antioxidants, proteases, and lipid peroxidation in wheat leaves

Two wheat (Triticum aestivum L.) genotypes with varying degree of drought tolerance were used to analyze programmed cell death (PCD) and related biochemical changes under drought stress. Drought induced PCD in leaves, as evident by internucleosomal nDNA fragmentation, was observed in sensitive genotype Nesser. Drought tolerant genotype (FD-83) showed higher peroxidase, superoxide dismutase, and catalase activities and ascorbate content under drought stress compared to sensitive genotype. Total phenolic content increased whereas lipid peroxidation remained un-changed under drought in FD-83. In contrast, drought enhanced the proteases and ascorbate peroxidase activities and lipid peroxidation (MDA content) in Nesser.     

Screening for drought tolerance in mutant germplasm of sesame (Sesamum indicum) probing by chlorophyll a fluorescence

Drought is one of the major constraints limiting crop productivity in African Sahel. The aim of this study was to select mutant sesame (Sesamum indicum L.) lines with improved levels of drought resistance. Twenty-one M4-M5 sesame lines of unknown drought tolerance, and their three parental sources with well-known and contrasting drought tolerance levels were evaluated at the vegetative stage in a factorial pot experiment, using a completely randomized design with three replicates. After 2 weeks of growth, water was withheld for 16 days as drought stress treatment. Chlorophyll a fluorescence data, as well as stomatal conductance and flag leaf temperature were recorded during the stress period. Recorded chlorophyll a fluorescence transients were analyzed by the JIP-test to translate stress-induced damage in these transients to changes in biophysical parameters allowing quantification of the energy flow through the photosynthetic apparatus. Large genotypic differences in the extent to which drought stress affected chlorophyll a fluorescence transients were observed. Drought stress reduced the performance index and stomatal conductance, and increased flag leaf temperature but had little effect on maximum quantum yield of primary photochemistry. A drought factor index is proposed in this work to screen for improved drought tolerance in twenty-one M4-M5 sesame lines. Mutant lines shi165, lc162, mc112, lc164, icn115, icn141, mt169, dwf172 and cc102 exhibited drought factor index values superior to those of the known drought tolerant cultivars Birkan and 38-1-7. A significant and negative relationship was found between the drought factor index and the leaf temperature index. Finally, we succeeded in obtaining drought tolerant lines with good secondary traits by using mutagenesis and chlorophyll fluorescence technique.     

Drought reduces floral resources for pollinators

Climate change is predicted to result in increased occurrence and intensity of drought in many regions worldwide. By increasing plant physiological stress, drought is likely to affect the floral resources (flowers, nectar and pollen) that are available to pollinators. However, little is known about impacts of drought at the community level, nor whether plant community functional composition influences these impacts. To address these knowledge gaps, we investigated the impacts of drought on floral resources in calcareous grassland. Drought was simulated using rain shelters and the impacts were explored at multiple scales and on four different experimental plant communities varying in functional trait composition. First, we investigated the effects of drought on nectar production of three common wildflower species (Lathyrus pratensis, Onobrychis viciifolia and Prunella vulgaris). In the drought treatment, L. pratensis and P. vulgaris had a lower proportion of flowers containing nectar and O. viciifolia had fewer flowers per raceme. Second, we measured the effects of drought on the diversity and abundance of floral resources across plant communities. Drought reduced the abundance of floral units for all plant communities, irrespective of functional composition, and reduced floral species richness for two of the communities. Functional diversity did not confer greater resistance to drought in terms of maintaining floral resources, probably because the effects of drought were ubiquitous across component plant communities. The findings indicate that drought has a substantial impact on the availability of floral resources in calcareous grassland, which will have consequences for pollinator behaviour and populations.     

Expression analysis of stress responsive pathway genes linked to drought hardiness in an adapted crop, finger millet (Eleusine coracana)

Drought is one of the major stresses limiting plant growth and productivity. Drought tolerance is regulated by multiple plant traits and examining the tolerance mechanisms from adapted species would assist in identification of novel pathways and superior genes. Since cellular tolerance is one of the major traits in drought acclimation we made in this study, an attempt to prospect candidate genes associated with the trait in drought hardy crop plant, finger millet (Eleusine coracana (L.) Gaertn). A novel gravimetric approach was employed to simulate field level drought stress for examining stress responsiveness of a few selected genes implicated in different stress response pathways. Gene expression was studied initially by e-northern analysis, and subsequently in leaf tissues experiencing different levels of drought stress by semi-quantitative and quantitative RT-PCR. A few stress responsive genes identified include metallothionein, farnesylated protein ATFP6, protein phosphatase 2A, RISBZ4 and farnesyl pyrophosphate synthase which probably have crucial roles in imparting hardiness to finger millet. Taken together the results suggest that multiple cellular tolerance pathways operate in a coordinated manner in drought tolerant crops.     

24-表油菜素内酯对干旱胁迫下辣椒叶片快速叶绿素荧光诱导动力学曲线的影响

以辣椒品种“超辣九号”为试材,采用15%的PEG6000模拟干旱,研究了0.1μmol·L^-1外源24-表油菜素内酯(EBR)处理对干旱胁迫下辣椒叶片快速叶绿素荧光诱导动力学曲线(OJIP)的影响。结果表明:干旱胁迫降低了辣椒叶片的光化学效率和光合性能,导致干旱光抑制的发生。干旱胁迫既损伤了辣椒叶片PSⅡ供体侧放氧复合体(OEC),同时也对PSⅡ反应中心和受体侧造成伤害,阻碍了光合电子传递;干旱胁迫还导致单位叶面积有活性反应中心数目(RC/CS)的下降,并降低了单位叶面积吸收的光能(ABS/CS)、捕获的光能(TRo/CS)和进行电子传递的能量(ETo/CS),同时诱导了单位叶面积热耗散(DIo/CS)的增加。这说明辣椒遭受干旱胁迫后启动了相应的防御机制,一方面通过PSⅡ的可逆失活减少光能吸收与传递,另一方面通过促进热耗散减少过剩激发能的积累。EBR处理改善了干旱胁迫下辣椒叶片PSⅡ受体侧的电子传递,缓解了单位叶面积有活性反应中心数目的减少,优化了光合电子传递的进行,并维持相对较高的热耗散能力,从而减轻了干旱光抑制程度,对干旱胁迫下辣椒叶片光合机构和光合性能起到保护作用。     

干旱胁迫下耐旱性小麦在不同生育期脱水素的表达分析

以2种耐旱性不同的盆栽小麦陕合6号(干旱耐受型)和郑引1号(干旱敏感型)为材料,分别在其苗期、分蘖期、拔节期、开花期对土壤实施不同程度的自然干旱胁迫和复水处理,采用SDS-PAGE和Western blotting技术研究其叶片脱水素的表达规律,探究小麦整个生长期脱水素的表达与干旱胁迫的关系.结果表明:2种小麦的脱水素均仅在干旱胁迫时表达,其中45 kD和37 kD的脱水素在2种小麦的4个发育期的叶片中均有表达,28 kD的脱水素仅在特定发育时期表达.在干旱耐受型小麦(陕合6号)中,脱水素在胁迫初期少量表达,随着胁迫程度加剧表达量急剧增加,在重度干旱胁迫下达到峰值,复水后小麦叶片中脱水素含量迅速下降;在干旱敏感型小麦(郑引1号)中,脱水素在胁迫初期大量表达,中度胁迫表达量小幅度回落,到复水1 d达到峰值,此后随着复水时间增加小麦叶片中脱水素的量逐渐下降.研究表明,小麦叶片脱水素表达与干旱胁迫程度和生育期迫密切相关,不同耐旱型小麦材料中叶片脱水素表达的差异与品种之间的干旱耐受能力密切相关.     

Drought effect on plant biomass allocation: A meta‐analysis

Drought is one of the abiotic stresses controlling plant function and ecological stability. In the context of climate change, drought is predicted to occur more frequently in the future. Despite numerous attempts to clarify the overall effects of drought stress on the growth and physiological processes of plants, a comprehensive evaluation on the impacts of drought stress on biomass allocation, especially on reproductive tissues, remains elusive. We conducted a meta‐analysis by synthesizing 164 published studies to elucidate patterns of plant biomass allocation in relation to drought stress. Results showed that drought significantly increased the fraction of root mass but decreased that of stem, leaf, and reproductive mass. Roots of herbaceous plants were more sensitive to drought than woody plants that reduced reproductive allocation more sharply than the former. Relative to herbaceous plants, drought had a more negative impact on leaf mass fraction of woody plants. Among the herbaceous plants, roots of annuals responded to drought stress more strongly than perennial herbs, but their reproductive allocation was less sensitive to drought than the perennial herbs. In addition, cultivated and wild plants seemed to respond to drought stress in a similar way. Drought stress did not change the scaling exponents of the allometric relationship between different plant tissues. These findings suggest that the allometric partitioning theory, rather than the optimal partitioning theory, better explains the drought‐induced changes in biomass allocation strategies.     

The misapplication of Hedwigia integrifolia P. Beauv. and identity of Gymnostomum imberbe Sm. (Hedwigiaceae,Bryopsida)

Abstract

We conducted a 6 year field experiment in an evergreen Quercus ilex forest where we simulated the increased drought projected by Global Circulation Models (GCM) and ecophysiological models for the immediate decades. We tested the hypothesis that enhanced drought will change C, N, P, K, Ca, Fe, Mg, Mo and S concentrations of the widespread moss Hypnum cupressiforme Hedw. and its capacity to absorb nutrients of soil-borne or airborne origin. During the period of study, from 1999 to 2005, the soil moisture in the drought treatment was on average 9% lower than the soil moisture in the control plots. Drought increased the K concentration by 10% and the C concentration by 6%, and decreased the Fe and Mo concentrations by 33% and 18%, respectively, and the N/P content ratio by 15%. A principal component analysis showed that 69% of the variation in moss elemental concentrations is explained by the drought treatment. Drought increased the enrichment factors of several elements, mainly of P, K, Ca, Mg, S and Mo, relative to bedrock extracts, thus showing that the proportion of these elements absorbed from the atmosphere had been increased by drought. The results show that drought increased the concentration of elements linked to drought resistance such as C and K, and decreased the contents of others important for plant productivity such as Mo and Fe. Drought thereby changed moss stoichiometry, and this could also affect the palatability and quite probably, the moss–herbivore relationships and decomposition rates.     

Effects of Drought Stress on Key Enzymes of Carbon Metabolism,Photosynthetic Characteristics and Agronomic Traits of Soybean at the Flowering Stage under Different Soil Substrates

Soybean is an important legume food crop, and its seeds are rich in nutrients, providing humans and animals with edible oil and protein feed. However, soybean is sensitive to water requirements, and drought is an important factor limiting soybean yield and quality. This study used Heinong 84 (drought resistant variety) and Hefeng 46 (intermediate variety) as tested varieties planted in chernozem, albic, and black soils. The effects of drought stress on the activities of key enzymes in carbon metabolism and photosynthetic characteristics of soybean were studied during the flowering stage, most sensitive to water. (1) The activities of SS-1, 6PGDH, and G6PDH enzymes in soybean leaves first increased and then decreased under drought stress. The enzyme activity was the highest under moderate drought stress and weakest in the blank group. (2) Drought stress increased Phi2, PhiNO, and Fm in soybean leaves and reached the highest value under severe drought; with the increase in drought stress, PhiNPQ and Fv/Fm of soybean leaves gradually decreased, reaching the lowest under severe drought. (3) With the increase in drought stress, F₀ and Fs of soybean leaves showed a single peak curve, and the maximum was at moderate drought. (4) Correlation analysis showed that F₀ was greatly affected by varieties and soil types; Fs, F0, and Fm soil varieties had a great influence, and chlorophyll fluorescence parameters were affected differently under drought stress with different drought degrees. (5) Drought stress changed the agronomic traits and yield of soybean. With the increase of drought degree, plant height, node number of main stem, effective pod number, 100-seed weight and total yield decreased continuously. (6) Drought stress affected the dry matter accumulation of soybean. With the increase of drought degree, the dry matter accumulation gradually decreased. Among them, the leaf was most seriously affected by drought, and SD decreased by about 55% compared with CK. Under the condition of black soil, the dry matter accumulation of soybean was least affected by drought.     

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.