Expansins are involved in cell growth mediated by abscisic acid and indole-3-acetic acid under drought stress in wheat

Expansin protein is a component of the cell wall generally accepted to be the key regulator of cell wall extension during plant growth. Plant hormones regulate expansin gene expression as well as plant growth during drought stress. However, the relationship between expansin and plant hormone is far from clear. Here, we studied the involvement of expansin in plant cell growth mediated by the hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) under osmotic stress which was induced by polyethylene glycol (PEG)-6000. Wheat coleoptiles from a drought-resistant cultivar HF9703 and a drought-sensitive cultivar 921842 were used to evaluate cell growth and expansin activity. Osmotic stress induced the accumulation of ABA. ABA induced expansin activity mainly by enhancing expansin expression, since ABA induced cell wall basification via decreasing plasma membrane H⁺-ATPase activity, which was unfavorable for expansin activity. Although ABA induced expansin activity and cell wall extension, treatment with exogenous ABA and/or fluridone (FLU, an ABA inhibitor) suggested that ABA was involved in the coleoptile growth inhibition during osmotic stress. IAA application to detached coleoptiles also enhanced coleoptile growth and increased expansin activity, but unlike ABA, IAA-induced expansin activity was mainly due to the decrease of cell wall pH by increasing plasma membrane H⁺-ATPase activity. Compared with drought-sensitive cultivar, the drought-resistant cultivar could maintain greater expansin activity and cell wall extension, which was contributive to its resultant faster growth under water stress.     

水稻幼苗叶绿体保护系统对干旱的反应

干旱条件下水稻耐旱品种湘中籼２号比不耐旱品种湘早籼１２号具有较低的质膜相对透性、叶绿素含量降低较少,表明耐旱品种受伤害较轻,两个品种的抗坏血酸。过氧化物酶（ＡｓＡ－ＰＯＤ）均降低,但耐旱品种降低较少。耐旱品种的谷胱甘肽还原酶（ＧＲ）活性在干旱初期提高,不耐旱品种的则变化不大。０．０１ｍｍｏｌ／Ｌ的百草枯和０．１ｍｍｏｌ／Ｌ的Ｈ２Ｏ２亦能诱导耐旱品种的ＧＲ活性,但对不耐旱品种的ＧＲ活性不受影响,说明可能是干旱诱导的氧化胁迫诱导了ＧＲ活性。干旱条件下两品种的抗坏血酸（ＡｓＡ）和还原型谷胱甘肽（ＧＳＨ）含量均是先升后降,但耐旱品种提高幅度较大。结果表明,耐旱品种的叶绿体保护系统的活性比不耐旱品种的高。     

Differential changes in cell wall matrix polysaccharides and glycoside-hydrolyzing enzymes in developing wheat seedlings differing in drought tolerance

The growth kinetics and variations in cell wall matrix polysaccharides and glycoside hydrolases during seedling development of the drought-tolerant wheat cultivar (cv. Hong Mang Mai) were compared with the drought-sensitive cultivar (cv. Shirasagikomugi). After 15d of culture in water at 22 degrees C under constant irradiance of 98mumolm(-2)s(-1), the length of the coleoptile and leaf sheath of Hong Mang Mai seedlings was 1.7 times longer than those of Shirasagikomugi seedlings. In the cell walls isolated from coleoptiles and leaf sheaths of the seedling of the two cultivars, the contents of arabinose, xylose, and glucose changed during development. The cell walls were fractionated progressively with 50mM CDTA, 50mM Na(2)CO(3), 1M KOH and 4M KOH, and sugar composition was determined. The amount of CDTA-soluble fraction from the Hong Mang Mai cell walls was 2.4-fold higher than that from the Shirasagikomugi cell walls at 6d of culture, and a considerable decrease was observed during development. The ratio of arabinose to xylose in 1M KOH-soluble fraction from the two cultivars decreased. The amount of 4M KOH-soluble fraction from the Shirasagikomugi cell walls was affected much more than those of the Hong Mang Mai cell walls. Many glycoside hydrolase activities were detected in the protein fractions from coleoptiles and leaf sheaths of the two cultivars, and the activities of licheninase, 1,3-1,4-beta-glucanase, and 1,3-beta-glucanase in the LiCl-soluble protein fraction increased drastically during development of the Shirasagikomugi seedlings. These findings suggest that the metabolism of the cell wall matrix polysaccharides of the drought-tolerant wheat cultivar is far different from that of the drought-sensitive wheat cultivar during seedling development.     

干旱胁迫对小麦幼苗根系生长和叶片光合作用的影响

采用水培试验方法,以2个耐旱性不同的小麦品种(敏感型望水白和耐旱型洛旱7号)为材料,研究了干旱胁迫对小麦幼苗根系形态、生理特性以及叶片光合作用的影响,以期揭示小麦幼苗对干旱胁迫的适应机制.结果表明： 干旱胁迫下,2个小麦品种幼苗的根系活力显著增大,而根数和根系表面积受到抑制;干旱胁迫降低了望水白的叶片相对含水量,提高了束缚水/自由水,而对洛旱7号无显著影响;干旱胁迫降低了2个小麦品种叶片的叶绿素含量、净光合速率、蒸腾速率、气孔导度和胞间CO2浓度,但随胁迫时间的延长,洛旱7号的叶绿素含量和净光合速率与对照差异不显著;干旱胁迫降低了2个小麦品种幼苗的单株叶面积,以及望水白的根系、地上部和植株生物量,而对洛旱7号无显著影响.水分胁迫下,耐旱型品种可以通过提高根系活力、保持较高的根系生长量来补偿根系吸收面积的下降,保持较高的根系吸水能力,进而维持较高的光合面积和光合速率,缓解干旱对生长的抑制.     

Effect of glycinebetaine on function of thylakoid membranes in wheat flag leaves under drought stress

Two wheat cultivars, HF9703 (drought tolerant) and SN215953 (drought sensitive) were used to examine the effects of glycinebetaine (GB, 100 mM) on lipid composition and function of thylakoid membranes under drought stress. GB application mitigated negative effect of drought on Ca²⁺-ATPase and Hill reaction activities, chlorophyll content, gas exchange and photosynthesis. These positive effects of GB application maybe, in part, correlated with improving the lipid composition of the thylakoid membranes.     

渗透胁迫下小麦根系渗透调节与根冠淀粉水解的研究

用不同浓度的PEG—600对抗旱性不同的小麦幼苗进行渗透胁迫处理,研究了小麦幼苗根系的淀粉酶活性、可溶性糖含量、渗透势、渗透调节能力和根冠淀粉的水解状况。结果表明,随着渗透胁迫程度的加重,抗旱性强的小麦品种昌乐5号和北农2号根系渗透势和饱和渗透势的降低程度大于抗旱性弱的小麦品种鲁麦5号和921842,并且抗旱性强的小麦品种根系的渗透调节能力大于抗旱性弱的小麦品种。随着渗透胁迫程度的加重．各品种小麦根冠淀粉粒均有不同程度的减少。而抗旱性强的品种根冠淀粉粒的减少程度小于抗旱性弱的品种;抗旱性强的小麦品种根系淀粉酶活性显著高于抗旱性弱的小麦品种,但是,随着渗透胁迫程度的加重,抗旱性弱的品种淀粉酶活性增加的幅度远高于抗旱性强的品种。可溶性糖含量的变化趋势与淀粉酶活性的变化趋势一致．即渗透胁迫下根冠淀粉水解程度大的小麦品种,可溶性糖的含量高。但根冠淀粉水解在根系的渗透调节以及在小麦适应水分胁迫中的作用还有待于进一步探讨。     

不同耐旱性水稻幼苗对氧化胁迫的反应

干旱条件下水稻(Oryza sativa L.)耐旱性较强的“湘中籼2号”比耐旱性较弱的“湘早釉12号”O_2~-的产生速率低。百草枯(0.01mmol/L)和H_2O_2(10mmol/L)处理促进干旱对水稻幼苗的伤害,但耐旱性较强的品种伤害较轻。单独用百草枯处理后,耐旱性较强的品种比耐旱性较弱的品种能更大幅度地提高超氧物歧化酶和过氧化物酶的活性;而H_2O_2处理后耐旱性较强的品种能提高过氧化氢酶活性。这些结果表明,耐旱性较强的水稻品种有较强的抗氧化胁迫能力。     

根施甜菜碱对干旱胁迫下小麦幼苗类囊体膜组分和功能的影响

干旱胁迫造成两小麦品系类囊体膜上的单半乳糖脂甘油二酯(MGDG)、双半乳糖脂甘油二酯(DGDG)、磷脂酰胆碱(PG)以及叶绿素含量显著下降,甜菜碱预处理能缓解这些组分的下降.干旱胁迫下,抗旱型小麦品系HF9 70 3的硫代异鼠李糖甘油二酯(SQDG)、反式十六碳-烯酸[16:1(3t)]含量显著上升,MGDG中亚麻酸(18:3)相对含量显著下降;而干旱敏感型品系SN215953则表现为SQDG、16:1(3t)含量显著下降,MGDG中脂肪酸变化不明显,这可能是两个小麦品系抗旱性差异的重要原因之一;甜菜碱处理能显著减小干旱处理与对照之间的差异,且对SN215953的作用较HF9703大.另外,干旱胁迫引起类囊体膜上Ca2 -ATPase活性、Hill反应活性及叶片净光合速率下降,外源甜菜碱能缓解其下降趋势.     

扩展蛋白与植物抗逆性关系研究进展

扩展蛋白是一种细胞壁蛋白,可调节细胞壁的松弛和伸展。目前研究表明,扩展蛋白几乎参与调节植物生长发育的整个进程。扩展蛋白还与植物的多种抗性反应有关,在植物对干旱、高盐以及病虫害等生物胁迫和非生物胁迫响应方面起着重要的调节作用。干旱胁迫下扩展蛋白基因的表达与植物的抗旱性有一定的关系;植物的耐盐性受到扩展蛋白基因表达的影响;淹水促进植物的伸长生长与扩展蛋白的表达密切相关;扩展蛋白调节细胞壁松弛为植物抗病性研究提供了新的思路。     

Comparative analysis of DNA methylation changes in two contrasting wheat genotypes under water deficit

DNA methylation is one of the epigenetic mechanisms regulating gene expression in plants in response to environmental conditions. In this study, analysis of methylation patterns was carried out in order to assess the effect of water stress in two contrasting wheat genotypes using methylation-sensitive amplified polymorphism (MSAP). The results revealed that demethylation was higher in drought-tolerant genotype (C306) as compared to drought-sensitive genotype (HUW468) after experiencing drought stress. Comparisons of different MSAP patterns showed a high percentage of polymorphic bands between tolerant and susceptible wheat genotypes (from 74.79 % at anthesis to 88.89 % at tillering). Furthermore, differential DNA methylation in roots and leaves also revealed tissue-specific methylation of genomic DNA. Interestingly, 54 developmental stage-specific bands and 23 bands that were found contrasting between these two wheat genotypes were detected. Furthermore, a few sites with stable DNA methylation differences were identified between drought-tolerant and drought-sensitive cultivars, thus providing genotype-specific epigenetic markers. These results not only provide data on differences in DNA methylation changes but also contribute to dissection of molecular mechanisms of drought response and tolerance in wheat.     

水分胁迫对抗旱性不同的荔枝叶片细胞壁H+-ATPase活性的影响

以抗旱性较强的荔枝东刘1号和抗旱性较弱的陈紫1－2年分盆栽实生幼苗为试验材料。研究了水分胁迫对荔枝（Litchi chinensis Sonn）叶片细胞胞质以及以离子键和共价键与细胞壁结合的H^ -ATPase活性的影响。结果表明：（1）叶片相对含水量随水分胁迫程度的增加而减少,抗旱性强的东刘1号下降的幅度小于抗旱性弱的陈紫。（2）H^ -ATPase在细胞中的分布是：细胞胞质H^ -ATPase占绝大多数,其次是共价键结合H^ -ATPase,离子键结合H^ -ATPase最少,品种间差异不明显。（3）在水分胁迫下,荔枝叶片H^ -ATPase活性（比活性）均上升,抗旱性强的品种上升的幅度均大于抗旱性弱的品种。     

Effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism in seedlings of wheat cultivars

The effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism (alpha and beta amylases, sucrose phosphate synthase, sucrose synthase, acid and alkaline invertases) in wheat (Triticum aestivum L.) was investigated in the seedlings of drought-sensitive (PBW 343) and drought-tolerant (C 306) cultivars. The water deficit was induced by adding 6% mannitol (water potential -0.815 Mpa) in the growth medium. The water deficit reduced starch content in the shoots of tolerant seedlings as compared to the sensitive ones, but increased sucrose content in the shoots and roots of tolerant seedlings, indicating their protective role during stress conditions. It also decreased the alpha-amylase activity in the endosperm of seedlings of both the cultivars, but increased alpha and beta amylase activities in the shoots of tolerant ones. Sucrose phosphate synthase (SPS) activity showed a significant increase at 6 days of seedling growth (DSG) in the shoots of stressed seedlings of tolerant cultivar. However, SPS activity in the roots of stressed seedlings of sensitive cultivar was very low at 4 DSG and appeared significantly only at day 6. Sucrose synthase (SS) activity was lower in the shoots and roots of stressed seedlings of tolerant cultivar than sensitive ones at early stage of seedling growth. Higher acid invertase activity in the shoots of seedlings of tolerant cultivar appeared to be a unique characteristic of this cultivar for stress tolerance. Alkaline invertase activity, although affected under water deficit conditions, but was too low as compared to acid invertase activity to cause any significant affect on sucrose hydrolysis. In conclusion, higher sucrose content with high SPS and low acid invertase and SS activities in the roots under water deficit conditions could be responsible for drought tolerance of C 306.     

Lipid Composition and Protein Dynamics in Thylakoids of Two Wheat Cultivars Differently Sensitive to Drought

Two wheat (Triticum durum Desf.) cultivars with different sensitivities to drought were either grown under regular irrigation or subjected to water deficit by withholding water for 14 d. Water-stressed plants of both cultivars underwent similar decreases in leaf water potential, but the drought-tolerant cultivar showed higher relative water content and turgor. Neither osmotic nor elastic adjustment mechanisms appeared to be active under the conditions described here. Thylakoids isolated from the stressed, drought-tolerant wheat showed an increase in lipid-to-protein ratio, in comparison with the control, whereas this ratio remained unchanged in the sensitive wheat. In both cultivars, water deficit determined different rearrangements in the composition of the thylakoid individual polar lipids, but their unsaturation level remained unaffected with the exception of monogalactosyldiacylglycerol. In the drought-sensitive cultivar, an accumulation of free fatty acids together with a reduction in polar lipid amount was observed. Electron paramagnetic resonance measurements of spin-labeled proteins of stressed plants from the sensitive cv Adamello showed a higher spin label rotational correlation time together with lower sulphydryl group and mobile proteic portion levels, in comparison with the control. In the tolerant cv Ofanto, the first two parameters changed to a lesser extent following water depletion, and the mobile proteic portion was not altered.     

Drought tolerance through over-expression of the expansin gene TaEXPB23 in transgenic tobacco

Expansins are proteins that are the key regulators of wall extension during plant growth. To investigate the role of TaEXPB23, a wheat expansin gene, we analyzed TaEXPB23 mRNA expression levels in response to water stress in wheat and examined the drought resistance of transgenic tobaccos over-expressing TaEXPB23. We found that the expression of TaEXPB23 corresponded to wheat coleoptile growth and the response to water stress. The results also indicated that the transgenic tobacco lines lost water more slowly than the wild-type (WT) plants under drought stress; their cells could sustain a more integrated structure under water stress than that of WT. Other physiological and biochemical parameters under water stress, such as electrolyte leakage, malondialdehyde (MDA) level, photosynthetic rate, F_v/F_m and ΦPSII, also suggested that the transgenic tobaccos were more drought resistant than WT plants.     

Differences in physiological characteristics between two wheat cultivars exposed to field water deficit conditions

We investigated various physiological characteristics of two wheat (Triticum aestivum L.) cultivars differing in drought tolerance, i.e., Shannong16 (a drought-tolerant cultivar) and Weimai8 (a high-yield wheat cultivar under well-watered conditions), under field drought conditions. The experiments were conducted over a two-year period. Drought stress (DS) was imposed by controlling irrigation and sheltering the plants from rain. Compared with Weimai8, Shannong16 exhibited the better water balance, the higher osmotic adjustment, the slower degradation of chlorophyll, and the higher net photosynthetic rate under drought-stress conditions. At the same time, we observed that Shannong16 maintained more integrated chloroplast and thylakoid ultrastructure in flag leaves than Weimai8 under field drought stress. The different levels of antioxidant competence, indicated by MDA content, antioxidant enzyme activities, and the level of superoxide radicals observed in the two wheat cultivars may be involved in the different levels of drought resistance of these cultivars.     

Relationship between osmotic stress and polyamines conjugated to the deoxyribonucleic acid-protein in wheat seedling roots

Polyamines (PAs) are biologically ubiquitous aliphatic amines that are implicated in many aspects of growth, development, sex differentiation, ripeness and senescence of plants[1―6]. It has been well documented that PAs are closely associated with plant …     

Relationship between osmotic stress and polyamines conjugated to the deoxyribonucleic acid-protein in wheat seedling roots

The contents of covalently conjugated polyamines (CC-PAs) and noncovalently conjugated polyamines (NCC-PAs) to deoxyribonucleic acid-protein (DNP) isolated from wheat (Triticum aestivum L.) seedling roots under osmotic stress were detected. Results showed that after osmotic stress treatment for 7 d, the levels in NCC-spermine (NCC-Spm) and NCC-spermidine (NCC-Spd) of drought-tolerant Yumai No. 18 cv. increased more markedly than that of drought-sensitive Yangmai No. 9 cv., while the NCC-putrescine (NCC-Put) could not be statistically detected in two cultivars. Exogenous Spm treatment alleviated osmotic stress injury to Yangmai No. 9 cv. seedlings, coupled with marked increases of NCC-Spm and NCC-Spd levels of this cultivar. Under PEG osmotic stress, the concomitant treatment of drought-tolerant Yumai No. 18 cv.seedlings with methylglyoxyl-bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), aggravated osmotic stress injury to this cultivar, coupled with market decreases of the NCC-Spm and NCC-Spd levels. The levels in CC-Put and CC-Spd of drought-tolerant Yumai No. 18 cv. increased more markedly than that of drought-sensitive Yangmai No. 9 cv. Under osmotic stress. The treatment of drought-tolerant Yumai No. 18 cv. seedlings with phenanthrolin (o-Phen), an inhibitor of transglutaminase (TGase), aggravated osmotic stress injury to this cultivar, coupled with a reduction of sum contents of CC-Put+CC-Spd. These results suggested that NCC-Spm and NCC-Spd, together with CC-Put and CC-Spd, in DNP of roots could enhance tolerance of the wheat seedlings to osmotic stress.