Carbohydrate Dynamics in Leaves of Rapeseed (Brassica napus) Under Drought

Until now, the carbohydrate dynamics in leaves of rapeseed under drought have largely been unknown. For this reason, a growth chamber study was conducted to examine whether the accumulation of carbohydrates under drought stress contributes to osmotic adjustment in leaf tissue. Plants of the cultivar Titan were subjected to temporary drought in the vegetative and reproductive stages. A third variant of long‐term drought covered the period from leaf development to flowering. The level of sucrose decreased under moderate water deficit, but accumulated under severe long‐term drought. Concentrations of glucose, fructose and trehalose were significantly enhanced and that of raffinose decreased in all the variants of drought. There was no evidence that any of the carbohydrates analysed in this study or the activities of soluble acid and cell wall invertases contributed to a drought‐induced accumulation of osmolytes. The results of this study indicate that osmotic adjustment in response to drought in leaves of the rapeseed cultivar Titan is only limited. It is virtually impossible that carbohydrates function as osmoprotectants in leaves of this cultivar, rising above that of the frequently detected accumulation of proline in rapeseed under water deficit.     

土壤干旱对小麦叶片渗透调节和光合作用的影响

本文研究了土壤干旱对小麦叶片渗透调节和光合作用的影响.小麦叶片水势、相对含水量、饱和渗透势、光合速率、蒸腾速率和气孔导度随土壤干旱程度加剧呈现出先缓降后陡降的趋势,其变化的土壤相对含水量阈值相同.小麦旗叶的渗透调节能力约为0.5MPa,不同叶位叶片渗透调节能力不同,其强弱顺序为旗叶>倒二叶>倒三叶.干旱使叶片膨压丧失时的渗透势从正常水分处理的-1.61MPa降到-2.33MPa,弹性模量从5.74MPa增加到6.35MPa.干旱条件下的光合速率、气孔导度、气孔限制值和叶片光合放氧能力都下降,而细胞间隙CO_2含量增加,说明光合速率的降低是非气孔因素即叶肉细胞光合活性限制的结果.     

土壤水分胁迫下小麦叶片的渗透调节与膨压维持

两年的试验结果表明,在土壤缓慢脱水和长期水分胁迫下,四个小麦品种叶片均产生渗透调节,孕穗期和灌浆期渗透调节能力较强,渗透调节的幅度为0.40～0.64MPa,抗旱性强的品种大于抗旱性弱的品种.由于渗透调节在土壤含水量60%左右或轻度胁迫下,叶片膨压基本不变.五个生育期四个处理水平叶水势与膨压回归分析,从水势每下降一个单位,膨压降低的单位数看,昌乐5号(0.146)<山农587(0.151)<烟农15(0.162)<济南13(0.240),抗旱性强的品种由于渗透调节能力强,膨压降低的单位数小,维持膨压的程度高.     

Effect of Drought and Nitrogen Availability on Osmotic Adjustment of Five Pearl Millet Cultivars in the Vegetative Growth Stage

Growth of pearl millet (Pennisetum glaucum (L.) R. Br.) is affected in areas with limited and erratic rainfall, often combined with nitrogen deficiency. Therefore, effects of severe drought and nitrogen availability on mechanisms of dehydration avoidance were investigated. Five pearl millet genotypes were cultivated in soil differing in nitrogen availability, low (N1), medium (N2) or high (N3) in a climate chamber. Thirty‐five days after sowing, the plants were exposed to drought for 12 days. Drought decreased leaf area and stomatal conductance strongly and caused leaf rolling. In the youngest fully expanded leaves, drought led to an osmotic adjustment from around ?0.5 to ?0.9 MPa, in N1 and N2 substantially achieved by potassium accumulation. Nitrate contributed to the osmotic adjustment in N2 and N3, proline only slightly, increasingly from N1 to N2, whereas the sum of glucose, fructose and sucrose did not play a role. The dehydration independent osmotic force for water uptake (osmotic potential at full turgor) was under drought strongest at N2 and in the landrace Dembi Yellow stronger than in the cultivars Ashana and Ugandi. This contributed to the higher relative water content (RWC) of ‘Dembi Yellow’, whereas due to other factors nitrogen had no effect on the RWC.     

Water Stress and Potassium Fertilization in Field Grown Maize (Zea mays L.): Effects on Leaf Water Relations and Leaf Rolling

Three cultivars of maize ( Zea mays L.) were grown in the experimental field at Hiroshima University, Japan under two levels of K fertilization with a non-irrigated water stress treatment and an irrigated control during June to August 1990. Leaf water potential, osmotic potential and stomatal conductance were measured 21 d after withholding water. Diurnal changes in degree of leaf rolling were measured on the 22nd day after withholding water. Leaf water potential and osmotic potential at full turgor were lower in the non-irrigated plants than irrigated and they were lower in the high K plants than the low K plants. Lowering of osmotic potential (osmotic adjustment) helped to maintain turgor under low water potential conditions. Turgor potential was increased by the higher K fertilization. Higher turgor potential may contribute to the higher stomatal conductance observed in non-irrigated high K plants. The degree of leaf rolling increased towards noon, and it was lower in high K plants than in low K plants. High K plants recovered from leaf rolling faster than the low K plants during the afternoon. High K. plants could maintain higher turgor potential throughout the day than the low K plants. Degree of leaf rolling was the lowest in the cultivar K-8388 which maintained the highest turgor potential via osmotic adjustment and it recovered from leaf rolling faster than the other two cultivars. Higher levels of K fertilization may be beneficial for maize plants to tolerate to water stress conditions.     

水分胁迫条件下高粱叶片的渗透调节及其对气孔导度和蒸腾速率的影响

两个抗旱性不同的高粱品种“3197B”和“三尺三”,在水分胁迫条件下,抗旱品种3197B渗透势降低,渗透调节能力较强.正常灌水时,两品种的气孔导度和蒸腾速率均随光照增强而增加,品种间差异不大;水分胁迫条件下,上午3197B气孔导度和蒸腾速率高于三尺三,午后水分胁迫严重时又低于三尺三,但其叶水势和膨压比三尺三高.     

Antioxidant and Photosynthetic Responses of Cotton to Soil Drought Stress during Flowering and Fruiting Stage

[Objective] The purpose of this study was to examine potential drought tolerance mechanisms in cotton (Gossypium hirsutum L.). Biochemical (antioxidant, protein and compatible osmolyte) and physiological (photosynthesis) responses to drought stress during the flowering and fruiting stages were examined. [Method] Using two cotton genotypes (A001 and A705) with different drought tolerance, a pot study was conducted in 2016 with treatments consisting of control (well-watered) and water stress. Water stress treatment was designed as withholding water from the pots until stomatal closure followed by limited water supply for 25 days where water-stressed plants received 40% of the optimum quantity of water. Measurements were made on soluble protein, proline and malonaldehyde (MDA) concentrations, peroxidase (POD) activity and photosynthetic characteristics (net photosynthetic rate P_n, transpiration rate E, stomatal conductance G_s) during the period of water stress. [Result] The soluble protein concentration was decreased and POD activity and MDA level were increased in the leaf subtending cotton boll of A001 under water deficit when compared with the control, but no response was observed in A705. Proline level responded to water deficit inconsistently between the two genotypes and across all sampling dates. Water stress significantly decreased P_n, E and G_s in the main stem leaves for both A001 and A705. [Conclusion] The results indicated that POD, soluble protein and MDA are involved in A001 and A705 responses to water deficit, and A705 is more tolerant to soil drought than A001.     

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψ_leaf) and its components and stomatal conductance (g_s) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC_w) of 22 dS m^?1. As water and salt stress developed and Ψ_leaf decreased, the leaf osmotic potential (Ψ_π) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ_leaf (with a steep drop at Ψ_leaf between ?0.8 and 1.2 MPa) and Ψ_π (with a steep drop at Ψ_π between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g_s. Leaf water potentials and g_s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ_leaf and turgor pressure, Ψ_p, vs. g_s) or linear (Ψ_leaf and Ψ_p vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψ_leaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ_π at full turgor. As soil was drying, the association between Ψ_leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.     

Cold acclimation in white clover subjected to chilling and frost: Changes in water and carbohydrates status

The effect of cold acclimation on the water status and the fate of carbohydrates was studied in white clover (Trifolium repens L., cv Huia) subjected to chilling and/or freeze-thaw cycles. Treatments were applied in a controlled environment, with a constant photoperiod, for 6 weeks to plants either acclimated or non-acclimated to low temperature.

Cold acclimated plants had a higher concentration of starch in the stolons at the end of the acclimation period than non-acclimated plants (54 vs. 15 mg g⁻¹ DW). During the experiment, the leaves of cold acclimated plants subjected to frosts maintained a higher relative water content (RWC) than did leaves of plants not acclimated for which we observed a strong dehydration of 80%.

Under chilling, cold acclimated plants demonstrated an osmotic adjustment. We showed that only 30–40% of the variation of the osmotic potential was explained by variation in free sugar concentration, suggesting that compounds other than carbohydrates participated in the osmotic regulation.

Chilling increased the carbohydrate content and frost decreased the starch concentration in non-acclimated plants only.

We showed in white clover that the cold acclimation contributed to frost and chilling tolerance by the maintenance of the hydration of tissues. We demonstrated that osmotic adjustment was not completely explain by the accumulation of free sugars.     

Remobilization of Proline and Other Nitrogen Compounds from Senescing Leaves of Maize under Water Stress

The effects of water stress around anthesis on proline accumulation and translocation from leaves of two maize cultivars (DA 4F37 and DA XL636) were studied. Water stress increased leaf proline content only in DA 4F37, while proline in leaf exudates was detected only in DA XL636 water-stressed plants. Proline translocation was not associated with increased nitrogen remobilization from leaves. The accumulating proline cultivar DA 4F37 showed a higher osmotic adjustment capacity than DA XL636. Leaf proline content in water-stressed DA 4F37 plants varied with daytime. High proline concentration during the morning was found in leaves with high relative water content. This evidence would support the hypothesis that proline is involved in osmotic adjustment.     

Yield and Osmotic Adjustment Capacity of Barley Under Terminal Water-Stress Conditions

This paper reports the influence of the osmotic adjustment capacity and turgor potential (TP) on tolerance to drought in 12 cultivated genotypes, six breeding lines and six cultivars of barley (Hordeum vulgare L.) under terminal water‐stress conditions. When the crops reached the flag leaf stage, half of the experimental plots in which they were grown were submitted to water stress treatment and the remainder maintained under optimal irrigation conditions. Differences were seen in the osmotic adjustment, relative water content (RWC) and water potential (WP) of the different genotypes. Two of the breeding lines showed the greatest osmotic adjustment capacities, maintaining their TPs better than the other genotypes studied. A positive, significant correlation was found between yield and osmotic adjustment capacity, RWC and WP under water‐stress conditions. Osmotic adjustment capacity and TP were linearly related, indicating that as water stress increases osmotic adjustment favours the maintenance of higher TPs. Significant correlations were found between osmotic adjustment capacity and grain filling rate and grain yield. Under conditions of terminal water stress, yield was negatively correlated with the number of days to ear emergence; no correlation was found between osmotic adjustment capacity and earliness. Early ear emergence, a good osmotic adjustment capacity and high RWC values all contributed to yield increases under terminal water‐stress conditions.     

Effects of Drought on the Sucrose Metabolism of Subtending Leaves of Cotton Bolls at Different Fruiting Branches and Boll Weight during Flowering and Bolling Stages

This study aimed to illustrate the mechanism of sucrose metabolism in subtending leaves of cotton bolls and its relationship with boll weight under drought stress during flowering and bolling stages. The 2-year-long experiments were conducted using pools of upland cotton(Gossypium hirsutum L.) plants, NuCOTN 33B, subjected to drought stress (relative water content reduced naturally until the boll opening stage) on the day of anthesis of the middle fruiting branches (MFB), using well-watered conditions as the control. The net photosynthetic rate declined under drought stress in the boll's subtending leaf, respectively, and the decline range was MFB>upper fruiting branch (UFB)>lower fruiting branch (LFB). Drought stress increased the soluble sugar contents of subtending leaves at LFB and UFB but decreased them at MFB. Sucrose content was increased and starch content decreased concomitantly, indicating that drought facilitated the partitioning of photosynthate into sucrose. Drought stress also depressed the activities of sucrose phosphate synthase and sucrose synthase, while acid invertase activity was initially decreased and then increased. The changes of MFB and UFB exceeded those of LFB, indicating that sucrose synthesis was inhibited, the degradation was first inhibited then promoted, causing a reduction in the amount of sucrose available for export. As a result, the boll weight declined during drought, and the decline range was MFB>UFB>LFB. In conclusion, the decreased sucrose synthesis and the impaired sucrose efflux of subtending leaves of bolls were the main causes for decreased boll weight under drought conditions during flowering and bolling stages of cotton.     

Synthesis of Osmotically Active Substances in Winter Wheat Leaves as Related to Drought Resistance of Different Genotypes1)

Water stress increased mono-saccharides and decreased di-saccharides concentration in four field grown genotypes, regardless of their different drought susceptibility. Sandy, a USA genotype known for giving satisfying yields in droughty environments, outstood the other cultivars in terms of betaine and proline concentration in leaf tissues; these aminoacids are therefore considered responsible for the most negative Ψs perceived in this cultivar. PV-curve technique revealed for Tullio, the drought susceptible Italian genotype, an osmotic adjustment of –0.63 MPa, four times greater than in Pandas, though this drought resistant cultivar showed a similar content in osmotically active substances; the authors therefore hypothesize an alternative mechanism in the response to water shortage in Tullio.     

Effect of Simulating Drought in Various Phenophases on the Water Use Efficiency of Winter Wheat

In Central Europe, drought is the most important limiting factor for autumn‐sown cereals. Due to the decline in groundwater, it is a priority to use less water‐demanding forms of crop production. Water use efficiency (WUE) can only be increased if cultivars with satisfactory water management traits are grown, so that they can exploit the water reserves of the soil even if drought occurs during the vegetation. Water consumption and water use efficiency of winter wheat genotypes were investigated in a model experiment carried out in a climate‐controlled glasshouse. The plants were grown either with optimum water supplies or with simulated drought in three phenophases, and measurements were made on the yield parameters, phenological traits and water use parameters of the plants. Substantial differences were observed between the water demands of the cultivars, and it was found that the later the phenophase in which drought was simulated, the greater the decline in water uptake. The analysis of WUE led to the conclusion that the WUE values of cultivars with short vegetation periods dropped to the greatest extent when water deficit was suffered at first node appearance, while cultivars with longer vegetation periods were more sensitive to drought during the heading and grain‐filling stages.     

Impact of nitrogen supply on leaf water relations and physiological traits in a set of potato (Solanum tuberosum L.) cultivars under drought stress

Improved adaptation of potato to limited water availability is needed for stable yields under drought. The maintenance of the cell water status and protection of cellular components against dehydration are important for drought tolerance, and the N status of plants affects the regulation of various respective metabolic processes. A 2‐year pot trial with 17 potato cultivars was conducted under a rain‐out shelter including two water regimes and two N‐levels to investigate genotypic differences concerning osmotic adjustment (OA) and relevant biochemical traits in relation to nitrogen (N) supply. Drought stress resulted in a rapid decrease in the leaf osmotic potential. The N, protein and proline contents increased under drought, while the N protein/N_Kjeldahl ratio decreased. Initially, total soluble sugars increased at both N‐levels but dropped back to the control level at high N‐availability under prolonged drought while remaining high in N‐deficient plants. Results indicate that potatoes have only a limited capacity of active OA and that increasing sugar and proline concentrations are rather associated with the protection of cellular components. High N supply promoted the N protein/N_Kjeldahl ratio at short‐term drought and enhanced proline accumulation. Significant genotypic differences were observed for all investigated traits.     

干旱条件下氮营养对小麦不同抗旱品种生长的影响

在土壤干旱条件下，３米小麦品种叶片水势、饱和渗透势、相对含水量、净光合速率、叶片导度、干物质积累量和籽粒产量均明显降低，且施氮小麦的下降幅度大于不施氮小麦，干旱削弱了氮素营养对小麦生长和产量的促进作用。土壤愈旱，渗透调节作用愈强，适当的氮素营养可增强渗透调节强度，水地型品种对水分和氮素营养均最敏感，其水分状况、游离脯氮酸含量，光合物质生产的产量的变化均较旱地型品种大；旱地型品种受旱时水分状况较稳定     

Soil drought duration and severity affect cotton boll biomass by altering recovery times and carbon dynamics of subtending leaf

Drought appears at flowering and boll formation for cotton frequently. However, reports on the impact of carbon dynamics in the subtending leaf on boll biomass under periodic droughts are limited. To investigate this, experiments were carried out with two cultivars (drought-tolerant: Dexiamian 1; drought-sensitive: Yuzaomian 9110), three water levels [soil relative water content (SRWC): control (75 ± 5)%, moderate drought (60 ± 5)%, severe drought (45 ± 5)%] and five drought durations (10, 17, 24, 31 and 38 days). A 38-day drought declined the net photosynthetic rate of subtending leaf, which could be collectively attributed to the reduction in carboxylation with reduced ribulose-1,5-bisphosphate carboxylase activity, and stomal limitation with decreased stomatal conductance, along with the damage of photosynthetic apparatus with depressed maximum and actual photochemical quantum yield, leading to lower starch content. A 38-day drought also increased the activities of sucrose phosphate synthase (SPS), sucrose synthase (Susy) and expressions of genes (GhSPS1, GhSPS2, GhSusA and GhSusB) associated with these enzymes, causing the accumulation of sucrose content, finally resulting in lower boll biomass. Some of the above parameters fully recovered under more than 17-day moderate drought or over 10-day severe drought, but boll biomass still decreased after re-watering. Under 10-day moderate drought, all aforementioned indices and boll biomass were completely recovered within 7 days of re-watering, and the recovery capacity of Yuzaomian 9110 was lower than that of Dexiamian 1. Therefore, rapid recovery of photosynthesis and decline in the subtending leaf sucrose content to pre-stress levels are important factors in lessening the impacts of drought on boll biomass and are indicative of cultivar tolerance to short-term moderate water deficit.     

Effect of Water Stress on Physiological Attributes and their Relationship with Growth and Yield of Wheat Cultivars at Different Stages

The effects of water stress on physiological attributes of drought‐sensitive (Kalyansona) and drought‐tolerant (C‐306) wheat cultivars were studied in a pot experiment. Water stress was imposed by withholding irrigation at boot and anthesis stages. Leaf water potential, leaf osmotic potential and leaf turgor potential (measured with pressure chamber and osmometer), as well as leaf diffusive resistance, leaf transpiration rate and leaf‐to‐air transpiration gradient (measured with a steady‐state porometer) were measured diurnally. Growth and yield parameters were recorded after harvesting of the crop. Triplicate data were analysed using a completely randomized design and correlations amongst these parameters were computed. Water stress was found to reduce diurnal leaf water potential and leaf osmotic potential in both the genotypes but leaf osmotic potential was significantly higher in the drought‐tolerant cultivar C‐306 than in the drought‐sensitive cultivar Kalyansona. Positive turgor was recorded in both the genotypes under water stress and non‐stress conditions. Water‐stressed plants showed significantly lower turgor potential than control plants. In diurnal observations, water‐stressed plants exhibited significantly higher leaf diffusive resistance in both genotypes at both stages. The diffusive resistance of C‐306 was predominantly higher than that of Kalyansona. Water stress decreased leaf transpiration rate at both stages but the reduction was higher at the anthesis stage. The leaf‐to‐air temperature gradient was much higher in C‐306 than in Kalyansona at the boot stage but at the anthesis stage genotypic variation was non‐significant. The capacity to maintain cooler foliage was lower at the anthesis stage than at the boot stage in both the cultivars. Shoot dry weight, number of grains, test weight, grain yield, biological yield and harvest index decreased to a greater extent when water stress was imposed at the anthesis stage, while imposition of water stress at the boot stage caused a greater reduction in plant height and number of tillers. Similarly, water stress caused a smaller reduction in growth, yield and yield attributes in C‐306 than in Kalyansona. In general, the correlation coefficient of grain and biological yield with water potential and its components was positive and highly significant. Similarly, turgor potential was also correlated positively and significantly with grain yield at both the stages, but with biological yield it was significant only at the anthesis stage. A negative and significant correlation was obtained for diffusive resistance and leaf‐to‐air temperature gradient with grain yield at the boot and anthesis stages. The rate of transpiration was also positively and significantly correlated to grain and biological yields at both the stages. Amongst the yield attributes, number of leaves and number of tillers were positively correlated at the anthesis stage, whereas leaf area and shoot dry weight were significantly correlated with grain and biological yields at both the stages.     

Atmospheric and soil water deficit induced changes in chemical and hydraulic signals in wheat (Triticum aestivum L.)

Plant responses to soil drying and the metabolic basis of drought-induced limitations in stomatal opening are still being discussed. In this study, we investigate the roles of root-born chemical and hydraulic signals on stomatal regulation in wheat genotypes as affected by soil drought and vapour pressure deficit. Twelve consecutive pot experiments were carried out in a glasshouse. Two bread wheat cultivars (Gönen and Basribey) were subjected to drought under high and low vapour pressure deficit (VPD) in a growth chamber. Total dry matter, specific leaf area, xylem ABA content, xylem osmotic potential, xylem pH, root water potential (RWP), stomatal conductance, leaf ABA content and photosynthetic activity were determined daily during 6 days after the onset of treatments (DAT). In the first phase of drought stress, soil drying induced an increase in the xylem ABA with a peak 3 DAT while RWP drastically decreased during the same period. Then the osmotic potential of leaves decreased and leaf ABA content increased 4 DAT. A similar peak was observed for stomatal conductance during the early stress phase, and it became stable and significantly higher than in well-watered conditions especially in high vapour deficit conditions (H-VPD). Furthermore, xylem pH and xylem osmotic potential appeared to be mostly associated with atmospheric moisture content than soil water availability. The results are discussed regarding possible drought adaptation of wheat under different atmospheric humidity.     

Mild Drought Stress‐Induced Changes in Yield,Physiological Processes and Chemical Composition in Festuca,Lolium and Festulolium

The impact of mild drought stress (3 weeks at 40 % field water capacity) on yield, physiological processes, accumulation of proline and phenolic compounds and forage quality parameters in forage grasses was evaluated in pot experiments. During four different growing periods, the effects of water deficit were assessed in nine varieties from five species (Lolium perenne, Lolium multiflorum, Festuca pratensis, Festuca arundinacea and Festulolium braunii). All measured parameters were affected by drought stress in the different cuts. Photosynthesis, transpiration rate, stomatal conductance and dry matter yield were significantly lower in drought stress than under well‐watered conditions in all varieties. Higher water‐use efficiency was only observed during the first and fourth drought period, while this was not the case in the second and third. Mild drought stress significantly increased the content of proline, phenolic acid, flavonoids, water‐soluble carbohydrates and protein. All tested grasses showed also an increase of organic matter digestibility and cell wall digestibility under drought stress conditions.