Hydraulic resistance of two sorghums varying in drought resistance

Genotypes of sorghum [Sorghum bicolor (L.) Moench] vary in drought resistance. Yet it is not known if their hydraulic resistances vary. The objective of this study was to determine if the hydraulic resistance of a drought-resistant sorghum was the same as that of a drought-sensitive sorghum. Leaf water and osmotic potentials were measured daily, during a 14-d period, in leaves of a drought-resistant (‘KS9’) and a drought-sensitive (‘IA25’) sorghum, which had the roots in pots with a commercial potting soil that was either well watered or allowed to dry. Soil water potential, adaxial stomatal resistance, and transpiration rate were determined daily. Hydraulic resistance of the plants was calculated from the slope of the line relating soil water potential minus leaf water potential versus transpiration rate. When the soil was not watered, the drought-sensitive sorghum had a water potential that averaged −0.50 MPa lower and an osmotic potential that averaged −0.57 MPa lower, but a similar adaxial stomatal resistance (1.19 s mm⁻¹), compared with the drought-resistant sorghum. Seven days after the beginning of the experiment, the water potential of the soil with the drought-sensitive sorghum was −0.25 MPa lower than that of the soil with the drought-resistant sorghum. With the water-limited conditions, the drought-sensitive sorghum depleted the soil-water reserve more quickly and died 2 d before the drought-resistant sorghum. Under well watered conditions, the two sorghums had similar water potentials (−1.64 MPa), osmotic potentials (−2.83 MPa), and adaxial stomatal resistances (0.78 s mm⁻¹). The calculated hydraulic resistance of the two sorghums did not differ and averaged 3.4 × 10⁷ MPa s m⁻¹. The results suggested that the variation in susceptibility to drought between the two genotypes was due to differences in rate of soil-water extraction. Contribution No. 86-249-J from the Kansas Agricultural Experiment Station. The paper is dedicated to the memory of Dr Dan M Rodgers.     

Water status of drought-resistant and drought-sensitive sorghum treated with ethephon

The effects of ethephon on stomatal resistance, water potential, osmotic potential, turgor potential, and ethylene production were determined on leaves of a drought-resistant (KS 65) and a drought-sensitive (IA 25) genotype of sorghum [Sorghum bicolor (L.) Moench] grown under wellwatered or drought-stressed conditions. With both sufficient and limited water supply, ethephon had no effect on the adaxial, abaxial, or total stomatal resistance of either genotype. For both water treatments, the adaxial stomatal resistance of the drought-sensitive genotype was higher than that of the drought-resistant genotype. Ethephon increased the amount of ethylene produced by the plants under both levels of water. For plants with sufficient water, water potentials of both genotypes were lowered by ethephon. Ethephon had no effect on the water potentials under drought or on the osmotic potentials under either water regime. With drought, the turgor potential of the drought-sensitive genotype, but not that of the drought-resistant, was increased by ethephon.     

Water status of drought-resistant and drought-sensitive sorghum treated with ethephon

The effects of ethephon on stomatal resistance, water potential, osmotic potential, turgor potential, and ethylene production were determined on leaves of a drought-resistant (KS 65) and a drought-sensitive (IA 25) genotype of sorghum [Sorghum bicolor (L.) Moench] grown under wellwatered or drought-stressed conditions. With both sufficient and limited water supply, ethephon had no effect on the adaxial, abaxial, or total stomatal resistance of either genotype. For both water treatments, the adaxial stomatal resistance of the drought-sensitive genotype was higher than that of the drought-resistant genotype. Ethephon increased the amount of ethylene produced by the plants under both levels of water. For plants with sufficient water, water potentials of both genotypes were lowered by ethephon. Ethephon had no effect on the water potentials under drought or on the osmotic potentials under either water regime. With drought, the turgor potential of the drought-sensitive genotype, but not that of the drought-resistant, was increased by ethephon.Contribution no. 90-147-J of the Journal Series of the Kansas Agricultural Experiment Station, Manhattan, Kansas, USA.     

Effects of plant growth regulators on the antioxidant system in callus of two maize cultivars subjected to water stress

The effects of brassinolide, uniconazole and methyl jasmonate on several aspects of antioxidant defences, were studied in callus tissues of drought-resistant (PAN 6043) and drought-sensitive (SC 701) cultivars of maize. When regulator-treated calli were subjected to water stress with PEG for 24 h the activities of antioxidant enzymes, such as superoxide dismutase, catalase, ascorbate peroxidase, peroxidase and glutathione reductase, remained higher in callus of the drought-resistant than in callus of the drought-sensitive cultivar. Damage, as indicated by the levels of hydrogen peroxide and malondialdehyde, the reduction of ascorbate and carotenoids, and leakage of electrolytes from cells was apparent in callus of both cultivars as a consequence of the applied water stress. However, the damage was less marked in the drought-resistant cultivar. The regulator-treated callus of this cultivar also had a higher survival percentage than that of the drought-sensitive cultivar.The present results also compare the effects of growth regulators on antioxidant systems in callus tissue of different drought-resistant cultivars when exposed to paraquat and water stress.     

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。     

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.     

Xylem ABA controls the stomatal conductance of field-grown maize subjected to soil compaction or soil drying

Stomatal conductance of individual leaves was measured in a maize field, together with leaf water potential, leaf turgor, xylem ABA concentration and leaf ABA concentration in the same leaves. Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf. The relationship between stomatal conductance and xylem [ABA] was common for variations in xylem [ABA] linked to the decline with time of the soil water reserve, to simultaneous differences between plants grown on compacted, non-compacted and irrigated soil, and to plant-to-plant variability. Therefore, this relationship is unlikely to be fortuitous or due to synchronous variations. These results suggest that increased concentration of ABA in the xylem sap in response to stress can control the gas exchange of plants under field conditions.     

Water and Osmotic Potentials of Ethephon-Treated Maize Genotypes Varying in Drought Resistance

Leaves of drought-resistant and drought-sensitive genotypes of maize (Zea mays L.) were sprayed with ethephon to determine its effect on water and osmotic potentials. With both sufficient and limited water supplies, ethephon decreased the water potential, but not the osmotic potential, of the drought-sensitive maize. It had no effect on the water and osmotic potentials of the drought-resistant maize under either water regime. The results showed that the response of a genotype of maize to ethephon depends upon its susceptibility to drought.     

Effects of water stress on the water relations of Phaseolus vulgaris and the drought resistant Phaseolus acutifolius

The tepary bean ( Phaseolus acutifolius Gray var. latifolius ), a drought resistant species, was compared under water stress conditions with the more drought susceptible P. vulgaris L. cvs Pinto and White Half Runner (WHR). In order to better understand the basis for the superior drought resistance of tepary, this study was designed to determine the relationships among leaf water potential, osmotic potential, turgor potential, and relative water content (RWC).
Plants were prestressed by withholding irrigation water. These stress pretreatments changed the relation between leaf water potential and relative water content of both species so that prestressed plants had lower water potentials than controls at the same leaf RWC. Tepary had lower water potentials at given RWC levels than Pinto or WHR; this can account for part of the superior resistance of tepary. In all genotypes, prestressed plants maintained osmotic potentials approximately 0.2 MPa lower than controls. Tepary reached osmotic potentials that were significantly lower (0.15 to 0.25 MPa) than Pinto or WHR. Both control and prestressed tepary plants had 0.05 to 0.25 MPa more turgor than Pinto or WHR at RWC values between 65 and 80%. Both prestressed and control tepary plants had greater elasticity (a lower elastic modulus) than Pinto or WHR. This greater turgor of tepary at low RWC values could be caused by several factors including greater tissue elasticity, active accumulation of solutes, or greater solute concentration.
Tepary had significantly lower osmotic potentials than the P. vulgaris cultivars, but there was little difference in osmotic potential between Pinto and WHR. Knowledge of differences in osmotic and turgor potentials among and within species could be useful in breeding for drought resistance in Phaseolus.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

小麦叶片光合作用与其渗透调节能力的关系

在缓慢干旱条件下,小麦叶片渗透调节能力在一定范围内随胁迫程度的加剧而增加,而在快速干旱下,渗透调节能力丧失。小麦叶片通过渗透调节使光合速率和气孔导度对水分胁迫的敏感性降低,叶片维持较高的电子传递能力、RuBP羧化酶活性和叶绿体光合能量转换系统活性,并推迟了小麦叶片光合速率受气孔因素限制向叶肉细胞光合活性限制转变的时间。     

Glycinebetaine application ameliorates negative effects of drought stress in tobacco

Two tobacco (Nicotiana tabacum L.) cultivars differing in drought tolerance were used to study the effects of foliar-applied glycinebetaine (GB, 80 mM) under well-watered and water-deficit conditions. The latter affected shoot biomass and height, with a more significant decrease observed in drought-sensitive cultivar than in drought-resistant cultivar. Foliar-applied GB was absorbed, accumulated by tobacco leaves and improved growth of plants subjected to water deficit. GB-treated plants maintained leaf water status apparently due to the improved osmotic adjustment. GB application enhanced the photosynthesis in water-deficit experiencing plants, mostly due to a greater stomatal conductance and carboxylation efficiency of CO₂ assimilation. photosystem II (PSII) activity in GB-treated plants was higher, as suggested by higher actual efficiency of PSII (ΦPSII). GB increased anti-oxidative enzyme activities under water deficit. All these effects resulted in an improved shoot biomass and height. Therefore, foliar GB application at the rapid growth stage favors plant growth in drought-stressed plants, mainly by improving water status and increasing PSII activity. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 4, pp. 534–541. The text was submitted by the authors in English.     

外源精胺对水分胁迫下小麦幼苗保护酶活性的影响

通过营养液培养试验,研究了水分胁迫下外源精胺(Spm)对抗旱性不同的小麦品种幼苗叶片质膜相对透性及保护酶活性的影响.结果表明:水分胁迫下,小麦叶片的质膜相对透性、M DA含量增加、SOD、CAT和POD活性上升,外源精胺处理可延缓水分胁迫下小麦叶片质膜相对透性和M DA含量上升,提高了SOD、CAT、POD酶活性的上升幅度;并且对抗旱性弱的品种保护酶活性增幅高于抗旱性强的品种.因此,外源精胺处理对抗旱性弱的品种缓解水分胁迫作用大于抗旱性强的品种.     

Relationship between carbohydrate partitioning and drought resistance in common bean

Drought is a major yield constraint in common bean (Phaseolus vulgaris L.). Pulse-chase (14)C-labelling experiments were performed using Pinto Villa (drought resistant) and Canario 60 (drought sensitive) cultivars, grown under optimal irrigation and water-deficit conditions. Starch and the radioactive label incorporated into starch were measured in leaves and pods at different time points, between the initiation of pod development and the production of mature pods. The water-stress treatment induced a higher starch accumulation in the drought-resistant cultivar pods than in those of the drought-sensitive cultivar. This effect was more noticeable during the early stages of pod development. Consistently, a reduction of starch content occurred in the leaves of the drought-resistant cultivar during the grain-filling stage. Furthermore, a synchronized accumulation of sucrose was observed in immature pods of this cultivar. These data indicate that carbohydrate partitioning is affected by drought in common bean, and that the modulation of this partitioning towards seed filling has been a successful strategy in the development of drought-resistant cultivars. In addition, our results suggest that, in the drought-resistant cultivar, the efficient carbon mobilization towards the seeds in response to water limitation is favoured by a mechanism that implies a more effective sucrose transport.     

Genotypic Variation in Leaf Water Potential, Stomatal Conductance and Abscisic Acid Concentration in Spring Wheat Subjected to Artificial Drought Stress

A technique for studying variation in the accumulation of abscisicacid (ABA) in response to drought stress is described. Two experiments,each testing 26 spring wheat genotypes, were carried out usingpot grown plants in controlled environment cabinets with nutrientsolution culture, though the results of only one experimentare described in detail. Plants were subjected to water stressby withholding water as the fifth or sixth leaf on the mainstem was emerging. Two stressed plants of each genotype wereharvested 5 and 7 days after the treatment commenced and measurementsof leaf water potential, stomatal conductance and ABA concentrationwere taken. There was considerable genotypic variation in the rate at whichwater potential decreased, partly explained by variation inplant size. Inia 66 (a genotype common to both experiments)had consistently much lower water potentials than the othergenotypes. Stomatal conductances of all genotypes decreasedrapidly and after 5 and 7 days they were negatively correlatedwith the changes in water potential. ABA concentrations varied considerably between genotypes afterboth 5 and 7 days without water, the variation being associatedwith genotypic differences in water potential on these occasions.The overall relationship between ABA concentration and waterpotential was highly significant. Significant differences betweenthe slopes of the regressions for individual genotypes werefound. The cultivar Sirius accumulated the most ABA at any waterpotential and Pelissier, Wascana and Hybrid 46 accumulated theleast. The significance for drought resistance of variation in ABAaccumulation is discussed. Triticum aestivum L. ABA, wheat, absasic acid, leaf water potential, stomatal conductance     

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。     

Relationship between osmotic stress-induced abscisic acid accumulation,biomass production and plant growth in drought-tolerant and -sensitive wheat cultivars

The effects of increasing osmotic stress induced by 100–400 mOsm (−0.976 MPa) polyethylene glycol (PEG 6000) were investigated in a drought-tolerant (Triticum aestivum L. cv. Mv Emese) and drought-sensitive (cv. GK élet) wheat cultivar at the three-leaf stage. During osmotic stress, the decline of the water potential (ψ _w) was more significant in the leaves, while the abscisic acid (ABA) levels of the roots increased earlier and remained higher in the sensitive than in the tolerant variety. There was an increasing gradient of ABA content toward the youngest leaves in the drought-sensitive GK élet, while more ABA accumulated in the fully developed, older leaves of the tolerant cultivar Mv Emese. In accordance with the rapid and significant accumulation of ABA, the stomatal conductance decreased earlier in the tolerant cultivar. The effect of water stress on the PSII photochemistry was pronounced only 1 week after the exposure to PEG, as indicated by the earlier decrease of the net CO₂ fixation, the effective quantum yield (Φ_PSII) and the photochemical quenching (q _P) in light-adapted samples of the tolerant variety in 400 mOsm PEG 6000. The stress treatment caused more significant reductions in these parameters toward the end of the experiment in the sensitive cultivar. In spite of small differences in the photosynthetic characteristics, the net biomass production was not significantly altered by this osmotic stress. The accumulation of ABA controlled the distribution of the biomass between the shoot and root systems under osmotic stress, and contributed to the development of stronger and deeper roots in the drought-sensitive cultivar GK élet. However, the root elongation did not correlate with the drought sensitivity of these cultivars on the basis of crop yield.     

Foliar abscisic acid content underlies genotypic variation in stomatal responsiveness after growth at high relative air humidity

Background and Aims

Stomata formed at high relative air humidity (RH) respond less to abscisic acid (ABA), an effect that varies widely between cultivars. This study tested the hypotheses that this genotypic variation in stomatal responsiveness originates from differential impairment in intermediates of the ABA signalling pathway during closure and differences in leaf ABA concentration during growth.

Methods

Stomatal anatomical features and stomatal responsiveness to desiccation, feeding with ABA, three transduction elements of its signalling pathway (H₂O₂, NO, Ca²⁺) and elicitors of these elements were determined in four rose cultivars grown at moderate (60 %) and high (90 %) RH. Leaf ABA concentration was assessed throughout the photoperiod and following mild desiccation (10 % leaf weight loss).

Key Results

Stomatal responsiveness to desiccation and ABA feeding was little affected by high RH in two cultivars, whereas it was considerably attenuated in two other cultivars (thus termed sensitive). Leaf ABA concentration was lower in plants grown at high RH, an effect that was more pronounced in the sensitive cultivars. Mild desiccation triggered an increase in leaf ABA concentration and equalized differences between leaves grown at moderate and high RH. High RH impaired stomatal responses to all transduction elements, but cultivar differences were not observed.

Conclusions

High RH resulted in decreased leaf ABA concentration during growth as a result of lack of water deficit, since desiccation induced ABA accumulation. Sensitive cultivars underwent a larger decrease in leaf ABA concentration rather than having a higher ABA concentration threshold for inducing stomatal functioning. However, cultivar differences in stomatal closure following ABA feeding were not apparent in response to H₂O₂ and downstream elements, indicating that signalling events prior to H₂O₂ generation are involved in the observed genotypic variation.     

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.