Expression analysis of a stress-modulated transcript in drought tolerant and susceptible cultivars of sorghum (Sorghum bicolor)

The present study reports the cloning of a 581 bp sequence, designated as SbEST8, from the osmotically stressed germinated seeds of a drought tolerant cultivar of sorghum (Sorghum bicolor). The SbEST8, which shows no homology with the reported gene sequences, is present in multiple copies and lacks restriction fragment length polymorphism among different sorghum cultivars. The expression of SbEST8 in the germinating seeds of sorghum was modulated by different abiotic stresses. Kinetic studies revealed that imposition of osmotic stress after 8h resulted in maximum levels of SbEST8 mRNA in the germinating seeds of cv. ICSV-272, with further stress causing a decline to undetectable levels by 16 h. However, relieving the stress after 12h resulted in an enhancement of SbEST8 mRNA levels for at least another 4h following which it declined. The decrease in SbEST8 mRNA levels in the leaves at 30 DAS in response to drought stress was observed only in the drought susceptible cultivar (CSV-216), whereas its expression was either increased substantially or remained unaffected in the tolerant cultivars, thus suggesting its role in water stress tolerance.     

Photosynthetic responses of Populus przewalski subjected to drought stress

Cuttings of P. przewalski were exposed to two different watering regimes which were watered to 100 and 25 % of field capacity (WW and WS, respectively). Drought stress not only significantly decreased net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), efficiency of photosystem 2 (PS2) (F_v/F_m and yield), and increased intrinsic water use efficiency (WUE_i) under controlled optimal conditions, but also altered the diurnal changes of gas exchange, chlorophyll fluorescence, and WUE_i. On the other hand, WS also affected the P _N-photosynthetically active radiation (PAR) response curve. Under drought stress, P _N peak appeared earlier (at about 10:30 of local time) than under WW condition (at about 12:30). At midday, there was a depression in P _N for WS plants, but not for WW plants, and it could be caused by the whole microclimate, especially high temperature, low relative humidity, and high PAR. There were stomatal and non-stomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, and low P _N at midday was caused by both stomatal and non-stomatal limitations, whereas non-stomatal limitation dominated in the afternoon. In addition, drought stress also increased compensation irradiance and dark respiration rate, and decreased saturation irradiance and maximum net photosynthetic rate. Thus drought stress decreased plant assimilation and increased dissimilation through affected gas exchange, the diurnal pattern of gas exchange, and photosynthesis-PAR response curve, thereby reducing plant growth and productivity.     

Mineral allocation to reproduction in Sorhum bicolor and Sorghum halepense in relation to parental nutrient supply

Summary This experiment investigated the effect of parental nutrient shortage on the allocation of five nutrients to seeds and rhizomes in Sorghum halepense, a perennial, noxious weed, and to seeds in Sorghum bicolor, an annual, cultivated species. Plants from both species were grown from seeds and supplied with fertilizer at three concentrations. The allocation of biomass and nutrients (N, P, K, Ca and Mg) to reproductive and vegetative parts was determined. Relative biomass allocation to reproduction (either sexual or vegetative) remained constant in S. halepense in spite of large differences in total plant weight. In S. bicolor, however, biomass allocation to sexual reproductive structures decreased significantly with decreasing nutrient supply. Individual seed weight was not modified by parental nutrient supply in S. halepense, but it increased with decreasing nutrient availability in S. bicolor. Important differences in mineral allocation to seeds were found between the two species. While S. bicolor seeds were largely buffered from the differences in parental nutrient status, concentration of nutrients in S. halepense seeds decreased significantly with decreasing supply for all the nutrients analyzed except Ca. However, mineral nutrient concentration in S. halepense rhizomes remained remarkably constant despite differences in the external supply, evincing the priority given to vegetative reproduction at the expense of sexual reproduction. Overall, the pattern of nutrient allocation in S. bicolor seeds under different nutrient supply resembled the pattern observed in S. halepense rhizomes, but it had little resemblance to the pattern of nutrient allocation in S. halepense seeds. The results are discussed in terms of differences and similarities in the reproductive strategy of these two species.     

Characterization of photosynthesis of Populus euphratica grown in the arid region

Net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (L_s) of Populus euphratica grown at different groundwater depths in the arid region were measured. g _s of the trees with groundwater depth at 4.74 m (D₄) and 5.82 m (D₅) were lower and a little higher than that at 3.82 m (D₃), respectively. Compared with C _i and L_s of the D₃ trees, C _i decreased and L_s increased at 4.74 m, however, Ci increased and L_s decreased at D₅. Hence photosynthetic reduction of P. euphratica was attributed to either stomatal closure or non-stomatal factors depending on the groundwater depths in the plant locations. P _N of the D₃ trees was significantly higher than those at D₄ or D₅. The trees of D₄ and D₅ did not show a significant difference in their P _N, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.     

干旱胁迫对日本荚蒾幼苗光合生理特性的影响

为了探讨极小种群野生植物日本荚蒾(Viburnum japonicum)对干旱胁迫的响应,以日本荚蒾二年实生苗为材料进行盆栽控水实验,设置正常供水(CK)、轻度干旱(LS)、中度干旱(MS)和重度干旱(SS)4个水分处理,研究持续干旱处理对日本荚蒾幼苗光合生理特性的影响。结果表明:在CK、LS、MS水分梯度下,日本荚蒾幼苗生长正常,但在SS胁迫下受影响明显,植株全部死亡。各胁迫阶段叶片净光合速率(P_n)、SPAD值、最大净光合速率(P_(nmax))、表观量子效率(AQY)、暗呼吸速率(R_d)表现出随水分梯度的降低而减小,光饱和点(LSP)、光补偿点(LCP)则相反,各水分梯度下AQY随时间延长逐渐上升,SS处理幼苗在胁迫45d及以后P_n均为负值。最大光化学效率(F_v/F_m)在胁迫过程中变化范围较小;实际光量子效率(ΦPSII)、电子传递速率(ETR)、光化学猝灭系数(qP)随土壤水分的减少而降低,非光化学猝灭系数(NPQ)逐渐上升,LS、MS与CK间变化幅度较小,但SS与CK间差距逐渐增大。结果表明在轻度和中度干旱下日本荚蒾幼苗表现出一定的适应性和耐干旱能力,而长期重度干旱则对幼苗影响较为严重。     

采煤塌陷影响下土壤含水量变化对柠条气孔导度、蒸腾与光合作用速率的影响

采煤塌陷引起的土壤环境因子的变化对矿区植物生长的影响越来越受到人们的关注,气孔导度、蒸腾与光合作用作为环境变化响应的敏感因子,研究植物气孔导度、蒸腾与光合作用的变化是揭示荒漠矿区自然环境变化及其规律的重要手段之一。研究采煤塌陷条件下植物光合生理的变化是探究煤炭开采对植物叶片水分蒸腾散失和CO_2同化速率影响的关键环节,是探讨采煤塌陷影响下植物能量与水分交换动态的基础,而采煤矿区植物叶片气孔导度、蒸腾与光合作用速率对采煤塌陷影响下土壤含水量变化的响应如何尚不清楚。选取神东煤田大柳塔矿区52302工作面为实验场地,以生态修复物种柠条为研究对象,对采煤塌陷区和对照区柠条叶片气孔导度、蒸腾和光合作用速率以及土壤体积含水量进行监测,分析了采煤塌陷条件下土壤含水量的变化以及其对柠条叶片气孔导度、蒸腾与光合作用速率的影响。结果显示:(1)煤炭井工开采在地表形成大量裂缝,破坏了土体结构,潜水位埋深降低,土壤含水量均低于沉陷初期,相对于对照区,硬梁和风沙塌陷区土壤含水量分别降低了18.61%、21.12%;(2)柠条叶片气孔导度、蒸腾和光合作用速率均与土壤含水量呈正相关关系;煤炭开采沉陷增加了地表水分散失,加剧了土壤水分胁迫程度,为了减少蒸腾导致的水分散失,柠条叶片气孔阻力增加,从而气孔导度降低,阻碍了光合作用CO_2的供应,从而导致柠条叶片光合作用速率的降低,蒸腾速率也显著降低。     

Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.This revised version was published online in March 2005 with corrections to the page numbers.     

米槁幼苗光合作用及光响应曲线模拟对干旱胁迫的响应

为阐明米槁光合作用对干旱胁迫的响应规律与适应机制,以一年生米槁幼苗为研究对象,进行盆栽试验研究设置3种不同土壤含水量梯度,利用Li-6400便携式光合作用系统测定干旱胁迫下的光合生理指标及光响应过程,光响应曲线模拟采用直角双曲线模型、非直角双曲线模型、指数模型和直角双曲线修正模型进行拟合并对比,以期选出适用于干旱环境下的光响应模型。结果表明(1)光响应曲线模型对干旱胁迫下米槁幼苗的光合作用拟合中直角双曲线、非直角双曲线和指数模型适用于低光合有效辐射(PAR),但拟合光响应参数与实测值相差大,只有直角双曲线修正模型能够很好的拟合各个处理且拟合参数比较精确米槁幼苗。(2)光合作用的表观量子效率(Φ)小于一般植物的光合量子效率,则其对弱光的光能利用效率相对较低。(3)在较强的光合有效辐射条件下,严重干旱胁迫下的米槁净光合速率P_n显著下降,出现了明显的光抑制现象;中度胁迫下净光合速率(P_n)、最大净光合速率(P_(nmax))、光补偿点(LSP)最大,米槁具有较宽的抗旱适应范围,有一定的抗旱性;严重胁迫下P_n、P_(nmax)、LSP降低,蒸腾速率(T_r)与气孔导度(G_s)下降幅度更大,但仍具有较高的水分利用效率(WUE),米槁在严重的干旱胁迫下光合机构受到一定的损伤,但自身可以通过生理调节来积极适应不良环境,减少光合机构伤害。(4)综合来看,在人工管理或种植米槁时,为了适应米槁生长发育,建议土壤含水量保持在23.05%到14.92%之间。     

多效唑和干旱胁迫对毛竹实生苗活力、光合能力及非结构性碳水化合物的影响

以1年生毛竹实生苗为研究对象,研究多效唑对不同水分条件下毛竹实生苗的叶绿素含量、光合参数、非结构性碳水化合物(NSC)含量、碳氮比、根系活力的影响。设置3个水分梯度:W1(75%相对田间持水量,CK)、W2(50%相对田间持水量,中度干旱)和W3(35%相对田间持水量,重度干旱),以及2个多效唑浓度:P1(0mg/L)、P2(40mg/L)。结果表明:随干旱强度增加,P1W1、P1W2、P1W3处理叶色逐渐变淡。与对照P1W1相比,P1W2和P1W3处理下叶绿素a、叶绿素b、类胡萝卜素、叶绿素a/b和叶绿素总含量显著下降(P0.05),Pn、Tr、WUE显著下降(P0.05),Ls显著上升(P0.05),毛竹叶片及根系中非结构性碳水化合物(NSC)含量显著上升(P0.05),毛竹根系活力显著下降。多效唑处理后,P2W2和P2W3的叶片色素含量相对于P2W1显著提高,但P2W2与P2W3无显著差异。同时,施加多效唑使Pn显著提高,P2W3较P1W3增加了146.9%。此外,P2W3处理使可溶性糖大量积累,达最大值3.41mg/g;毛竹叶片及根系淀粉含量显著上升,根系活力显著提高。试验揭示了多效唑通过提高干旱水平下毛竹实生苗的根系活力、光合速率,增加光合色素、非结构性碳水化合物含量,并将养分从地上转移到地下部分,进而抵御干旱胁迫带来的伤害。     

6种草本植物对干旱胁迫和CO2浓度升高交互作用的生长响应

以CO2浓度升高为主要标志的全球气候变化及由其引起的极端气候变化对陆地生态系统产生了重要的影响。利用步入式CO2生长室模拟研究了CO2浓度变化(400和700μL/L)和干旱胁迫(水分充足CK:100%FC(田间持水量);中度干旱MS:40%FC;重度干旱SS:20%FC)的交互作用对草本植物网果酸模(Rumex chalepensis)、野豌豆(Vicia sepium)、泥胡菜(Hemmistepta lyrata)、风轮菜(Clinopodium chinense)、藜(Chenopodium album)和玉米石(Sedum album)生长特性的影响。结果表明:CO2浓度升高总体上刺激了网果酸模、野豌豆、泥胡菜、风轮菜和藜这5种C3植物在任何水分条件下的生长,也刺激了玉米石在水分条件较好下的生长;干旱胁迫总体上抑制了所有6种植物的生长,但中度干旱胁迫有刺激CAM植物玉米石生长的趋势。CO2浓度升高能否缓解干旱的负面影响具有明显的种间差异:CO2浓度升高减缓了干旱胁迫对泥胡菜和风轮菜的负面影响,这种缓解作用在网果酸模和野豌豆中显著降低,对藜没有明显的促进作用,对干旱下的玉米石的生长却起到了抑制作用。CO2浓度升高总体上增加了根质量分数和干物质含量;干旱胁迫明显提高了6种草本植物的根生物量的分配比例,降低了干物质含量;但CO2浓度升高和干旱胁迫的交互作用可导致不同的物种产生不同的响应,说明植物能够通过调节生物量分配和植株本身的水分含量保持能力来适应CO2浓度和干旱胁迫的交互影响,这种调节能力取决于植物在碳的吸收和水分散失之间的平衡"trade-off"。研究结果有助于增进草本植物对未来气候变化的适应性理解,为评估和预测全球气候和水文变化对植物的生理生态影响提供理论依据。     

干旱胁迫下紫花苜蓿幼苗非结构性碳水化合物代谢对NO的响应

以紫花苜蓿（Medicago sativa）为材料,采用盆栽试验方法,用聚乙二醇（PEG-6000）作为渗透介质模拟干旱胁迫,外源喷施NO供体硝普钠,NO清除剂（carboxy-PTIO,cPTIO）,对紫花苜蓿幼苗叶片、根系中非结构性碳水化合物含量及相关酶活性的变化进行研究,探讨NO对紫花苜蓿耐旱机制的作用。结果表明：外源NO促进了紫花苜蓿叶片中淀粉的分解、根系中淀粉的积累,提高叶片及根系中可溶性糖（蔗糖、果糖和葡萄糖）含量,降低了渗透势,促进细胞吸水,缓解干旱造成的损伤。此外,外源NO能提高干旱胁迫下紫花苜蓿叶片中蔗糖合成酶（SS）、酸性转化酶（AI）和中性转化酶（NI）活性,降低了蔗糖磷酸合成酶（SPS）的活性,提高根系中SS、SPS和转化酶活性,使蔗糖的合成与分解处于高水平的动态平衡,增强了紫花苜蓿的抗旱性。而NO清除剂cPTIO则会不同程度的抑制紫花苜蓿幼苗中非结构性碳水化合物（NSC）及其相关酶活性。因此,NO可以通过调控NSC的代谢响应干旱胁迫,缓解干旱胁迫造成的不利影响,在紫花苜蓿的抗旱中扮演着重要的角色。     

前期水淹对牛鞭草后期干旱胁迫光合生理响应的影响

水淹和干旱是限制植物生长的两种主要环境因子。三峡库区消落带由于其特殊的地形条件和人工水文节律,呈现以年度为周期的“水淹-落干”交替变化的水文变动特征,在消落带生长的植物因此受到水淹和干旱交替胁迫的双重影响。为了探究库区蓄水对消落带植被干旱耐受性的影响,以当年生牛鞭草扦插苗为试验对象,设置对照组(CK)、表土水淹组(SF)、全淹组(TF)、对照-干旱组(CD)、表土水淹-干旱组(SFD)、全淹-干旱组(TFD)6个处理组,研究不同水分处理对牛鞭草光合特性的影响。结果表明:(1)水淹和干旱胁迫均对牛鞭草光合特性造成显著影响;(2)水淹胁迫阶段,与CK组相比,牛鞭草SF和TF组净光合速率、气孔限制值和水分利用效率显著下降,胞间CO_2浓度显著上升;(3)干旱胁迫阶段,牛鞭草CD和SFD组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等光合参数显著低于CK组,TFD组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等指标与CK组无显著差异;(4)复水阶段,各处理组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等指标均与CK组无显著差异。研究表明,前期水淹并未增加牛鞭草对后期干旱胁迫的敏感性,牛鞭草对水淹和干旱胁迫均具有较好的耐受性,有助于牛鞭草对库区消落带生境变化的适应性。     

Screening for drought tolerance in Sorghum using cell culture

Summary Callus growth from 10 cultivars ofSorghum bicolor (L.) Moench was measured with increasing levels of polyethylene glycol (PEG) as an osmoticum in the medium to determine whether differences among these cultivars at the cellular level in response to osmotic stress existed. These cellular ratings were compared to field ratings from the 10 tolerant-to-susceptible cultivars when grown under drought conditions to determine whether cellular ratings corresponded to differences in drought tolerance at the plant level. Callus cultures were grown on Murashige and Skoog inorganic salt formulation plus vitamins, 2,4-dichlorophenoxyacetic acid (2,4-D), kinetin and sucrose, supplemented with 0 to 25% (wt/vol) PEG corresponding to −0.2 to −1.62 MPa osmotic potential. Results suggest that PEG-induced osmotic stress on callus cultures can be used to screen sorghum cultivars for potential early field (preflowering) drought tolerance. This implies that at least a component of the early field drought tolerance in sorghum may have a cellular basis. This study was supported by U.S. Agency for International Development Grant AID/DSAN/XII/G-0149, and USDA Competitive Grants Program.     

Chromosome endoreduplication as a factor of salt adaptation in Sorghum bicolor

Summary. Nuclear DNA amounts were measured by Feulgen cytophotometry in Sorghum bicolor cv. 610 plants early exposed to 150 mM NaCl, a treatment known to induce an increased tolerance to salinity in plants carrying this genotype. In salt-treated plants, the percentages of 8C, 16C, and 32C nuclei in roots in the primary state of growth were 21.9%, 13.3%, and 4.3%, respectively. By contrast, in nonsalinized plants, only 3.5% of the nuclei had an 8C content and no higher DNA contents were observed. The salt treatment induced chromosome endoreduplication during the differentiation of cells in the root cortex, where 41.2% of the cells displayed a DNA content higher than 4C (versus 1.3% in control plants). No enhancement of endopolyploidy was observed in cells of the root vascular cylinder or the leaves of the salt-treated plants. In another S. bicolor genotype (DK 34-Alabama), noncompetent for salt adaptation, the same NaCl treatment did not induce chromosome endoreduplication in root cortex cells. Endopolyploidy may be considered as a part of the adaptive response of S. bicolor competent genotypes to salinity. Correspondence and reprints: Dipartimento di Biologia Cellulare e Ambientale, Università di Perugia, Via A. Pascoli, 06123 Perugia, Italy.     

Differences in drought sensitivities and photosynthetic limitations between co-occurring C3 and C4 (NADP-ME) Panicoid grasses

Background and Aims

The success of C₄ plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C₄ grasses are not necessarily less sensitive to drought than C₃ grasses and are proposed to respond with greater metabolic limitations, while the C₃ response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C₃ and C₄ NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response.

Methods

Six species of locally co-occurring grasses, C₃ species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C₄ (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO₂ concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types.

Key Results

Leaves of C₄ species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C₄ photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO₂ assimilation, whereas, in the C₃ species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C₄ plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C₃ plants which recovered a greater proportion of photosynthesis through increased stomatal conductance.

Conclusions

Within the Panicoid grasses, C₄ (NADP-ME) species are metabolically more sensitive to drought than C₃ species and recover more slowly from drought.     

Changes of leaf water potential and gas exchange during and after drought in triticale and maize genotypes differing in drought tolerance

Influence of drought (D) on changes of leaf water potential (Ψ) and parameters of gas exchange in D-resistant and D-sensitive genotypes of triticale and maize was compared. Soil D (from −0.01 to −2.45 MPa) was simulated by mannitol solutions. At −0.013 MPa significant differences in Ψ, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and internal CO₂ concentration (C _i) of D-resistant and D-sensitive triticale and maize genotypes were not found. Together with the increase in concentration of the mannitol solution the impact of D on E and g _s for D-sensitive genotypes (CHD-12, Ankora) became lower than for the D-resistant ones (CHD-247, Tina). Inversely, impact of D on Ψ was higher in D-sensitive than D-resistant genotypes. From 1 to 3 d of D, a higher decrease in P _N was observed in D-resistant genotypes than in the D-sensitive ones. Under prolonged D (5–14 d) and simultaneous more severe D the decrease in P _N was lower in D-resistant than in D-sensitive genotypes. Changes in Ψ, P _N, E, and g _s caused by D in genotypes differing in the drought susceptibility were similar for triticale and maize. Compared to control plants, increase of C _i was different for triticale and maize genotypes. Hence one of the physiological reasons of different susceptibility to D between sensitive and resistant genotypes is more efficient protection of tissue water status in resistant genotypes reflected in higher decrease in g _s and limiting E compared to the sensitive ones. Other reason, observed in D-resistant genotypes during the recovery from D-stress, was more efficient removal of detrimental effects of D.     

珍稀濒危植物堇叶紫金牛对持续干旱的生理响应

采用盆栽控水法,研究了珍稀濒危植物堇叶紫金牛(Ardisia violacea)在持续干旱条件下的生理响应。随着持续干旱时间的延长,堇叶紫金牛应对持续干旱的阶段可分为适应期、轻度干旱期、中度干旱期和重度干旱期。在适应期和轻度干旱期,堇叶紫金牛叶片游离脯氨酸和可溶性糖含量稳定在一个较低水平,可溶性蛋白质含量先下降后快速上升,细胞膜系统和抗氧化酶系统能主动进行生理调节;中度干旱期,丙二醛(MDA)含量和质膜相对透性迅速升高,细胞膜系统受损加剧,游离脯氨酸、可溶性糖含量均急剧增加,对抵御干旱起到重要的渗透调节作用。在轻度干旱期和中度干旱期,光合色素中叶绿素a和叶绿素b含量显著提高,以抵抗干旱胁迫。重度干旱期,细胞膜系统、抗氧化酶SOD、游离脯氨酸和可溶性糖含量上升,但MDA略微下降,这时可能达到植物耐受干旱的极限,不再发生膜脂过氧化作用。综上表明,堇叶紫金牛具有较强的耐旱性,RWC为49.94%是细胞膜系统、抗氧化酶系统和渗透调节物质含量变化的拐点,渗透调节和抗氧化酶系统的主动适应是其耐旱的主要机制。     

Growth and Gas Exchange of Three Sorghum Cultivars Under Drought Stress

A field study was conducted to evaluate the drought tolerance of three sorghum [Sorghum bicolor (L.) Moench] cultivars, Gadambalia, Arous elRimal and Tabat, and quantify the physiological bases for differences in their drought tolerance. Water stress reduced shoot dry mass of Gadambalia, Arous elRimal and Tabat by 43, 46 and 58 %, respectively. The respective reduction in leaf area of the three cultivars was 28, 54 and 63 %. The reduction in net photosynthetic rate, stomatal conductance and transpiration rate due to water stress was lowest in Gadambalia and highest in Tabat. The leaf water potentials and relative water contents of Gadambalia under wet and dry treatments were similar, while those of Tabat were significantly reduced by water stress. The lowest and highest liquid water flow conductance was displayed by Tabat and Gadambalia, respectively. Drought tolerance in Gadambalia is associated with its smaller leaf area, higher liquid water flow conductance, and ability to maintain high leaf water potential, relative water content, stomatal conductance, transpiration rate and photosynthetic rate under drought stress. This revised version was published online in July 2006 with corrections to the Cover Date.