Nodule Structure and Functioning in Chickpea (Cicer Arietinum) as Affected by Salt Stress

Cicer arietinum L. plants raised in sand culture under natural light were subjected to salinity stress induced by mixture of NaCl, CaCl₂, MgCl₂ and MgSO₄ (40, 60 or 80 meq dm^-3). Acetylene reduction activity (ARA) of nodules, leghemoglobin content and nodule structure were followed 55, 75 and 85 d after sowing. ARA declined significantly under salt treatments and the lowest ARA was observed at day 85 after sowing. Decrease in ARA was consistent with decreased nodule leghemoglobin content. The leghemoglobin content of control plants decreased by 50 % at day 85 indicating senescence of nodules. This senescence was further accelerated by salt treatment after which the leghemoglobin content fell to negligible levels. The structural changes associated with salt stress were mainly reduction in size of the nodules, decreased meristematic zone, reduced number and degradation of symbiosomes, reduced intercellalar spaces and deposition of electron dense material in the intercellular spaces in the cortex of nodules.     

Changes in seed water status as characterized by NMR in developing soybean seed grown under moisture stress conditions

Changes in water status of developing seeds of Soybean (Glycine max L. Merrill.) grown under different moisture stress conditions were characterized by proton nuclear magnetic resonance (NMR)- spin–spin relaxation time (T₂). A comparison of the seed development characteristics, composition and physical properties indicated that, characteristics like seed weight, seed number/ear, rate of seed filling increased with development stages but decreased with moisture stress conditions. The NMR- spin–spin relaxation (T₂) component like bound water increased with seed maturation (40–50%) but decreased with moisture stress conditions (30–40%). The changes in seed water status to increasing levels of moisture stress and seed maturity indicates that moisture stress resulted in more proportion of water to bound state and intermediate state and less proportion of water in free-state. These changes are further corroborated by significant changes in protein and starch contents in seeds under high moisture stress treatments. Thus seed water status during its development is not only affected by development processes but also by moisture stress conditions. This study strongly indicated a clear moisture stress and development stage dependence of seed tissue water status in developing soybean seeds.     

Nitrogen Fixation (C(2)H(2) Reduction) by Broad Bean (Vicia faba L.) Nodules and Bacteroids under Water-Restricted Conditions

Water potentials of leaves and nodules of broad bean (Vicia faba L.) cultivated on a sandy mixture were linearly and highly (r² = 0.99) correlated throughout a water deprivation of plants. A decrease of 0.2 megapascal of the nodule water potential (Ψ_nod) induced an immediate 25% inhibition of the highest level of acetylene reduction of broad bean nodules attached to roots. This activity continued to be depressed when water stress increased, but the effect was less pronounced. Partial recovery of optimal C₂H₂ reduction capacity of mildly water stressed nodules (Ψ_nod = −1.2 megapascals) was possible by increasing the external O₂ partial pressure up to 60 kilopascals. The dense packing of the cortical cells of nodules may be responsible for the limitation of O₂ diffusion to the central tissue. Bacteroids isolated from broad bean nodules exhibited higher N₂ fixation activity with glucose than with succinate as an energy-yielding substrate. Bacteroids from stressed nodules appeared more sensitive to O₂, and their optimal activity declined with increasing nodule water deprivation. This effect could be partly due to decreased bacteroid respiration capacity with water stress. Water stress was also responsible for a decrease of the cytosolic protein content of the nodule and more specifically of leghemoglobin. The alteration of the bacteroid environment appears to contribute to the decline in N₂ fixation under water restricted conditions.     

The effect of ammonium nitrate on the synthesis of nitrogenase and the concentration of leghemoglobin in pea root nodules induced by Rhizobium leguminosarum

The effects of NH₄NO₃ on the development of root nodules of Pisum sativum after infection with Rhizobium leguminosarum (strain PRE) and on the nitrogenase activity of the bacteriods in the nodule tissue were studied. The addition of NH₄NO₃ decreased the nitrogenase activity measured on intact nodules. This reduction of nitrogen fixation did not result from a reduced number of bacteroids or a decreased amount of bacteroid proteins per gram of nodule. The synthesis of nitrogenase, measured as the relative amount of incorporation of [³⁵S]sulfate into the components I and II of nitrogenase was similarly not affected.The addition of NH₄NO₃ decreased the amount of leghemoglobin in the nodules and there was a quantitative correlation between the leghemoglobin content and the nitrogen-fixing capacity of the nodules. The conclusion is that the decrease of nitrogen-fixing capacity is caused by a decrease of the leghemoglobin content of the root nodules and not by repression of the nitrogenase synthesis.     

Water relations and nitrogen fixation in potassium fedVigna radiata nodules

Drought created by withholding the irrigation at 30 and 45 d after sowing significantly decreased relative water content (RWC) and osmotic potential (ψ_s) ofVigna radiata (L.) Wilczek cv. MH-83-30 nodules. Potassium fed plants showed higher RWC, whereas ψ_s was further declined irrespective of soil moisture levels. The nitrogenase activity and leghemoglobin content of nodules markedly decreased under drought and nodules of potassium fed plants showed better recovery after rehydration. The proline content significantly increased under drought but declined upon reirrigation. Also, the C, N and K contents of nodules significantly declined under drought.     

Changes in secondary metabolites and fiber quality of cotton (Gossypium hirsutum) seed under consecutive water stress and in silico analysis of cellulose synthase and xyloglucan endotransglucosylase

Global warming has led to severe drought conditions. The selection of plant varieties that can withstand drought and produce increased yields are of utmost importance. In the current study, secondary metabolites, seed trait and fiber characteristic of cottonseeds (Gossypium hirsutum) exposed to double and third water stress exposure was investigated. Total phenol and tannin content in W₁S₃₃ increased significantly after third water stress exposure. Accumulation of wax was enhanced in seeds of W₃S₃₃ and W₃S₃₄ that were subjected to third water stress. Fiber quality parameters decreased when cottonseeds were rainfed. High irrigation resulted in fragile and delicate fiber. Seeds grown under 66% FC irrigation saved water and produced seeds that had the potential of producing high quality fibers. In silico analysis was performed on cellulose synthase A (CesA) and xyloglucan endotransglycosylase (XET) enzymes present in Gossypium hirsutum. The intracellular locations of the CesA and XET1 enzymes are the plasma membrane and cell wall, respectively. Proline is conserved in the C-terminal of the CesA enzyme and plays an important role in enzyme functionality. This study provides a better understanding as to the mechanisms by which the plant can tolerate and combat water stress conditions as well as reduce water consumption. In order to grow cotton seeds with desirable morphometric characteristics and optimal fibers under water stress exposure and in dry areas, it is better to use seeds that are irrigated under optimal irrigation conditions, ie 66% FC.     

Foliar Application of Cytokinin Modulates Gas Exchange Features,Water Relation and Biochemical Responses to Improve Growth Performance of Maize under Drought Stress

Improvement of plant performance under drought stress is crucial to sustaining agricultural productivity. The current study investigated the ameliorative effects of foliar-applied kinetin, an adenine-type cytokinin (CK), on growth and gas exchange parameters, water relations and biochemical attributes of maize plants under drought stress. Eighteen-day-old maize plants were subjected to drought by maintaining soil moisture content at 25% field capacity for 8 days followed by foliar application of kinetin at 0, 75, 150 and 225 mg L⁻¹ (CK0, CK75, CK150 and CK225, respectively) to the plants for two-times at the 9-day interval. Results revealed that drought stress markedly reduced stem diameter, dry weight, chlorophyll content, gas exchange parameters and water balance but increased proline, malondialdehyde and soluble sugar contents, electrolyte leakage and senescence in maize leaves. Application of exogenous CK remarkably improved maize performance by modulating growth, gas exchange- and water relation-related parameters in a dose-dependent manner under drought stress. CK225 increased chlorophyll content (by 61.54%), relative water content (by 49.14%), net photosynthesis rate (by 39.94%) and transpiration rate (by 121.36%) and also delayed leaf senescence but decreased internal CO₂ concentration (by 7.38%), water saturation deficit (by 40.40%) and water uptake capacity (by 42.49%) in both well-watered and drought-stressed plants. Nevertheless, CK application considerably decreased electrolyte leakage, proline, malondialdehyde and soluble sugar levels in drought-stressed maize plants, as also supported by heatmap and cluster analyses. Taken together, exogenous CK at proper concentration (225 mg L⁻¹) successfully improved maize performance under drought conditions, thereby suggesting CK application as a useful approach to alleviate drought-induced adverse effects in maize plants, and perhaps in other important crop plants.     

Effects of water deficit on N2(C2H2) fixation in cowpea and groundnut

The effect of water deficit on nodulation, N₂ fixation, photosynthesis, and total soluble sugars and leghemoglobin in nodules was investigated in cowpea and groundnut. Nitrogenase activity completely ceased in cowpea with a decrease in leaf water potential ( _leaf) from –0.4 MPa to –0.9 MPa, while in groundnut it continued down to –1.7 MPa. With increasing water stress, the acetylene reduction activity (ARA) declined very sharply in cowpea, but ARA gradually decreased in groundnut. Even with mild water stress ( _leaf of 0.2 MPa), nodule fresh weight declined 50% in cowpea partly due to a severe nodule shedding whereas nodule fresh weight declined in groundnut only when _leaf decreased by 1.0 MPa. No nodule shedding was noticed even at a higher stress level in groundnut. Photosynthesis and stomatal conductance were also more stable in groundnut than in cowpea under water stress. There was a sharp increase in total soluble sugars and leghemoglobin in the nodules of groundut with water stress, but no definite trend could be found in cowpea.     

Interactive Effects of Soil Nutrients, Moisture and Sand Burial on the Development, Physiology, Biomass and Fitness of Cakile edentula

The relative importance and interactive effects of nutrientsupply, soil moisture content and sand burial on the development,physiology, biomass allocation and fitness ofCakile edentulawere examined under controlled greenhouse conditions. Planttraits were more frequently affected by nutrient supply thanby soil moisture content or sand burial. Measurements on mostplant traits also varied depending on the two or three way interactionsamong the three environmental factors. Plants partially buriedby sand had higher leaf chlorophyll concentration than thoseunburied at the early stages of development, especially underlow soil moisture content. High nutrient supply tended to lowerthe leaf chlorophyll concentration of mature plants, and thiseffect was more pronounced under high as compared to low soilmoisture content. High nutrient supply enhanced the photosyntheticcapacity of plants when they were water stressed. With adequatesoil moisture, high nutrient supply increased/decreased thephotosynthetic capacity of plants with/without previous experienceof water stress. High nutrient supply increased the biomassallocation to the root system of plants, especially at low soilmoisture content. Partial sand burial also promoted biomassallocation to the root system of plants grown at low soil moisturecontent. Soil nutrition; water supply; sand accretion; multiple stresses; biomass allocation; Cakile edentula     

Photosynthetic responses of wheat (Triticum aestivum L.) to combined effects of drought and exogenous methyl jasmonate

Drought stress limits wheat growth and productivity. The response of wheat (Triticum aestivum L.) to different water supply conditions (well-watered and drought-stressed) and exogenous methyl jasmonate (MeJA; 0 and 0.25 μM) was studied. The application of MeJA enhanced wheat adaptability to drought stress by physiological and metabolic adjustments. Drought stress reduced net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), and water-use efficiency (WUE) in wheat. The application of exogenous MeJA decreased also g _s and E, but stimulated WUE. Meanwhile, MeJA mitigated the decline of P _N, g _s, and WUE induced by drought stress and midday depression by 6–183%. Both drought stress and exogenous MeJA induced stomatal closure, which improved water status and delayed plant senescence. MeJA enhanced the activities of superoxide dismutase, peroxidase, catalase, and reduced malondialdehyde content. P _N-PAR response curves showed that MeJA mitigated the decline of maximum P _N, apparent quantum yield, and saturation irradiance, and the increase of compensation irradiance. Drought stress and exogenous MeJA increased dark respiration rate and showed an additive effect. These results indicated that 0.25 μM MeJA enhanced the photosynthesis under drought stress mainly by improving the water status and antioxidant capacity of wheat.     

Effects of water stress on photosynthesis and nitrogen metabolism in vegetative and reproductive shoots of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

In Leymus chinensis, mild water stress (soil moisture 60–65 % of field capacity) had no significant effects on nitrogen metabolism, photosynthesis, and chlorophyll fluorescence. Severe water stress (35–40 %) significantly decreased the activities of nitrate reductase, glutamine synthetase, and glutamate dehydrogenase, net photosynthetic rate, stomatal conductance, transpiration rate, maximal efficiency of photosystem 2 photochemistry (F_v/F_m), actual quantum yield, and photochemical quenching, but increased the endopeptidase activity and malondialdehyde contents. The adverse effects on photosynthesis and N metabolism were markedly greater in reproductive shoots than in vegetative shoots.     

Effects of water stress and rewatering on photosynthesis,root activity,and yield of cotton with drip irrigation under mulch

Soil water deficit is a major limitation to agricultural productivity in arid regions. Leaf photosynthesis can quickly recover after rewatering and remains at a higher level for a longer period, thus increasing crop yield and water-use efficiency (WUE). We tested our hypothesis that leaf photosynthesis and root activity of water-stressed cotton (Gossypium hirsutum L.) plants could quickly recover after rewatering at a certain growth stage and it should not influence a cotton yield but increase WUE. Treatments in this study included two degrees of water stress: mild water stress (V₁) and moderate water stress (V₂) imposed at one of four cotton growth stages [i.e., S₁ (from the full budding to early flowering stage), S₂ (from early flowering to full flowering), S₃ (from full flowering to full bolling), and S₄ (from full bolling to boll-opening)]. The soil water content before and after the water stress was the same as that in the control treatment (CK, 70–75% of field capacity). Water deficit significantly reduced the leaf water potential, net photosynthetic rate, and stomatal conductance in cotton. The extent of the decline was greater in S₂V₂ treatment compared to others. Water deficit also reduced root activity, but the extent of inhibition varied in dependence on soil depth and duration. When plants were subjected to S₁V₁, the root activity in the 20–100 cm depth recovered rapidly and even exceeded CK one day after rewatering. An overcompensation response was observed for both photosynthesis and aboveground dry mass within one to three days after rewatering. Compared with the CK, S₁V₁ showed no significant effect on the yield but it increased total WUE and irrigation WUE. These results suggest that even a short-term water stress during the S1, S2 and S4 stages mitigated, with respect to the root activity, the negative effect of drought and enhanced leaf photosynthesis compensatory effects of rewatering in order to increase cotton WUE with drip irrigation under mulch in arid areas.     

Limiting Factors in Photosynthesis: I. USE OF IRON STRESS TO CONTROL PHOTOCHEMICAL CAPACITY IN VIVO

The possibility of using Fe stress as an experimental tool in the study of limiting factors was explored. Results show that Fe stress decreased the chlorophyll (Chl) a, Chl b, carotene, and xanthophyll content of leaves of sugar beets (Beta vulgaris L.) and that the maximum rate of photosynthetic CO₂ uptake (P_max) per unit area was linearly related to Chl (a + b) per unit area. Measurements of noncyclic ATP formation by isolated chloroplasts at light saturation indicate that photosynthetic electron transport capacity decreased concomitantly with pigment content under Fe stress.     

贝壳砂生境干旱胁迫下杠柳叶片光合光响应模型比较

以黄河三角洲贝壳堤岛3年生杠柳(Periploca sepium)苗木为试验材料, 模拟设置贝壳砂生境下的4种水分梯度, 利用CIRAS-2型光合作用系统测定杠柳叶片在不同干旱胁迫下的光合作用光响应过程, 采用4种光响应模型进行拟合分析, 以比较贝壳砂生境干旱胁迫下适宜的光响应模型, 探讨最佳光响应模型参数对干旱胁迫的适应规律。结果表明: 4种模型对杠柳叶片光合作用光响应过程拟合效果的优劣顺序为: 直角双曲线修正模型>非直角双曲线模型>指数模型>直角双曲线模型, 后3种模型均为没有极值的函数, 故不能很好地拟合光响应曲线光抑制过程, 并不能直接求解最大净光合速率(P_nmax)和光饱和点(LSP)。光响应参数拟合效果最佳表现为: 非直角双曲线模型的暗呼吸速率(R_d), 直角双曲线模型的光补偿点(LCP), 直角双曲线修正模型的P_nmax和LSP。4种光响应模型对干旱胁迫具有不同的适应性, 直角双曲线修正模型适应各种水分条件, 直角双曲线模型和指数模型较适合轻度干旱胁迫条件, 非直角双曲线模型较适合重度干旱胁迫条件。随干旱胁迫的加剧, 光响应参数表观量子效率(AQY)、R_d和LCP先升高后下降, 净光合速率(P_n)、P_nmax和LSP逐渐下降。轻度、中度和重度干旱胁迫下, LSP分别比对照下降5.2%、16.3%和34.5%, P_nmax分别比对照下降17.8%、39.0%和59.0%。水分充足条件下, 杠柳叶片光能利用最强, 光照生态幅最宽; 重度干旱胁迫下, 杠柳叶片表现出明显的光饱和、光抑制现象, 光能利用减弱, 光合能力受到较大限制。     

Effects of nitrogen nutrition on xylem sap composition of Casuarinaceae

Summary Effect of moisture stress on photosynthesis activity ofSpartina alterniflora was studied using sediment cores taken from a Louisiana Gulf Coast salt marsh. Moisture stress was induced by evapotranspiration losses which simulate conditions that can occur when a salt marsh is not inundated by tidal cycles for extended periods. Changes in the sediment moisture from 70% to 28% when expressed as a percentage of the wet weight resulted in a rapid decrease in net CO₂ fixation. The moisture content of this sediment remained above saturation throughout the experiment although the solute or osmotic potential was equivalent to being in the range between field capacity and permanent willing. Net fixation was correlated with the moisture content (r=0.92^**). Plant photosynthetic activity decreased at sediment moisture levels below 70%.     

Photosynthetic performance and acclimation of <Emphasis Type="Italic">Incarvillea delavayi</Emphasis> to water stress

The photosynthetic performance and related leaf traits of Incarvillea delavayi Bur. et Franch were studied at different water regimes to assess its capacity for photosynthetic acclimation to water stress. The initial response of I. delavayi to water stress was the closure of stomata, which resulted in down-regulation of photosynthesis. The stomatal limitation (S_L) represented the main component to photosynthetic limitations but non-stomatal limitation (NS_L) increased quickly with the increasing water stress, and had similar magnitude to SL under severe water stress (soil moisture 25–30 % of field capacity). Chlorophyll (Chl) a fluorescence parameters characterizing photosystem (PS) 2 photochemical efficiency (Φ_PS2), electron transport rate (J) and photochemical quenching (qP) decreased with the increasing water stress, indicating impaired photosynthetic apparatus. However, the water-stressed plants had a increased mesophyll CO₂ diffusional conductance, Chl a/b ratio, leaf nitrogen partitioning in RuBPCO and bioenergetics in later grown parts, indicating that I. delavay had a substantial physiological plasticity and showed a good tolerance to water stress.     

Root morphology ion absorption and antioxidative defense system of two Chinese cabbage cultivars (Brassica rapa L.) reveal the different adaptation mechanisms to salt and alkali stress

Salt stress and alkali stress are major factors that affect the growth and production of Chinese cabbage. To explore their tolerant mechanism to salt and alkali stress, three salinity levels (0, 50, 100 mmol/L NaCl) and three different pH levels (pH6.5, pH7.5, pH8.5) were interactively applied on Qinghua (salt-tolerant–alkali-sensitive) and Biyu (salt-sensitive–alkali-tolerant) cultivars; the root morphology, ion content and antioxidant enzymes were determined. The results showed that the root morphology and root water content of Qinghua under S₀pH_7.5 and S₀pH_8.5 were seriously affected, and the content of H₂O₂ and MDA increased by 143%, 190% and 234%, 294%, respectively, compared with S₀pH_6.5; when Biyu was under S₅₀pH_6.5 and S₁₀₀pH_6.5 stress, the content of H₂O₂ and MDA increase to 152%, 208% and to 240%, 263%, respectively, but the activities and genes expression of SOD, POD, CAT, AAO, APX, DHAR and MDHAR did not change. The root and the contents of H₂O₂ and MDA were not affected when Qinghua was treated with salt and Biyu was treated with alkali, but the activities of the antioxidant enzymes increased to 150–200%, and their relative expression was overexpressed and 2.5–3.5-fold of the S₀pH6.5. The increase of Na⁺ in Qinghua was limited under salt stress, Mg²⁺ in Biyu increased significantly under alkali stress. These all indicated that the adaptability of roots could reflect the degree of tolerance; Chinese cabbage with high salt and alkali tolerance enhanced the regulation of their absorption of ions and increased the relative expression and activities of related antioxidant enzymes.

     

干旱胁迫下胡杨光合光响应过程模拟与模型比较

以塔里木干旱荒漠区2年生胡杨幼苗为试材,盆栽模拟荒漠生境5种水分梯度,利用Li-6400便携式光合作用系统测定胡杨在干旱胁迫下光合作用的光响应过程,并采用4种光响应模型对其进行拟合与比较,以期优选出适用于干旱荒漠环境的光响应模型,阐明胡杨光合作用对干旱胁迫的响应规律与适应机制。结果表明:胡杨净光合速率(P_n)随干旱胁迫加剧呈下降趋势,同一光强(PAR)下P_n降幅增大。中度干旱胁迫以下(土壤相对含水量,RSWC45%)胡杨在高PAR下仍能维持相对较高P_n,光抑制程度轻;直角双曲线、非直角双曲线和指数模型均可较好地模拟P_n-PAR响应过程,但最大净光合速率(P_(nmax))、光饱和点(LSP)拟合值与实测值差异极显著(P0.01)。中度干旱胁迫以上(RSWC45%)胡杨P_n随PAR升高而显著下降,LSP与P_(nmax)极显著降低,光抑制现象明显;仅直角双曲线修正模型拟合的胡杨光响应过程、光响应参数与实际情况较吻合。4种模型模拟效果顺序:直角双曲线修正模型指数模型非直角双曲线模型直角双曲线模型。4种光响应模型对干旱胁迫具有不同的适应性,直角双曲线修正模型适用于各种水分条件,尤其适用于干旱荒漠生境,其它3种模型适用于水分条件较好的生境。光响应特征参数对干旱胁迫的响应阈值不同。随干旱胁迫加剧,胡杨表观量子效率(AQY)、P_n、LSP与P_(nmax)持续降低,严重干旱胁迫下暗呼吸速率(R_d)、LCP反而明显增大。RSWC45%胡杨仍能保持较高的AQY、P_(nmax)、LSP,RSWC45%其P_(nmax)、LSP显著降低,干旱胁迫显著抑制了胡杨光合进程和光强耐受范围,降低了光合效率,严重干旱胁迫严重影响胡杨苗木的正常生长和光合作用。干旱荒漠环境下,胡杨采取缩窄光照生态幅、降低光能利用率和减少呼吸消耗来积极抵御荒漠干旱逆境伤害的生态对策。因此,从极端干旱荒漠区种群保护与植被恢复角度来看,胡杨林土壤水分应维持在RSWC 50%左右,符合干旱缺水地区植物生长和高效用水的管理原则。     

Response of stem sap flow and leaf photosynthesis in <Emphasis Type="Italic">Tamarix chinensis</Emphasis> to soil moisture in the Yellow River Delta,China

Soil moisture is the main limiting factor for vegetation growth at shell ridges in the Yellow River Delta of China. The objective of this study was to explore the soil moisture response of photosynthetic parameters and transpiration in Tamarix chinensis Lour., a dominant species of shell ridges. Leaf photosynthetic light-response parameters and sap flow were measured across a gradient of relative soil water content (RWC), from drought (23%) to waterlogging (92%) conditions. Leaf photosynthetic efficiency and stem sap flow of T. chinensis showed a clear threshold response to soil moisture changes. Leaf net photosynthetic rate, water-use efficiency (WUE), light-saturation point, apparent quantum yield, maximum net photosynthetic rate, and dark respiration rate peaked at moderately high RWC, decreasing towards high and low values of RWC. However, peak or bottom RWC values substantially differed for various parameters. Excessively high or low RWC caused a significant reduction in the leaf photosynthetic capacity and WUE, while the high photosynthetic capacity and high WUE was obtained at RWC of 73%. With increasing waterlogging or drought stress, T. chinensis delayed the starting time for stem sap flow in the early morning and ended sap flow activity earlier during the day time in order to shorten a daily transpiration period and reduce the daily water consumption. The leaf photosynthetic capacity and WUE of T. chinensis were higher under drought stress than under waterlogging stress. Nevertheless, drought stress caused a larger reduction of daily water consumption compared to waterlogging, which was consistent with a higher drought tolerance and a poor tolerance to waterlogging in this species. This species was characterized by the low photosynthetic capacity and low WUE in the range of RWC between 44 and 92%. The RWC of 49–63% was the appropriate range of soil moisture for plant growth and efficient physiological water use of T. chinensis seedlings.     

The effect of methanol on photosynthetic parameters of bean (Phaseolus vulgaris L.) under water deficit

Water availability is the main factor limiting crop growth and productivity in dry regions. This study was carried out in order to determine the effect of spraying methanol solution on the photosynthetic characteristics of bean plants. The main aim of our experiment was to improve plant performance under stress caused by water shortage. Two factors were involved: water-deficit stress, such as severe stress (25% of field capacity), mild stress (75% of field capacity), and no stress (100% of field capacity), and application of methanol solution spray at four concentrations: control (without spraying), 10, 20, and 30%. Methanol was applied three times at different growth stages (seedling, flowering, and podding stage) in 10-d intervals. The treatment with 20% methanol at the seedling stage resulted in increased net photosynthesis (P_N), intercellular CO₂ concentration (C_i), and decreased transpiration rate (E) under no stress and mild stress conditions. Under severe stress, 10 and 20%-methanol treatments resulted in increased C_i, maximal quantum yield of PSII photochemistry, and decreased E. At the flowering stage, methanol treatments resulted in decreased E and increased C_i under mild and severe stress. At the podding stage, 10 and 20%-methanol treatments resulted in increased P_N, C_i, and total chlorophyll content under mild stress. In conclusion, we suggested that foliar application of methanol had a positive role in enhancing photosynthetic performance.