Influence of Silicon on Sunflower Cultivars under Drought Stress,I: Growth,Antioxidant Mechanisms,and Lipid Peroxidation

Abstract: Understanding plant responses to drought stress is essential, and there is a need to know possible physiological mechanisms of damage and drought avoidance for the genetic improvement of crops. Therefore, we investigated the effects of silicon (Si) on shoot and root growth, leaf relative water content (RWC), stomatal resistance (SR), lipid peroxidation (MDA), membrane permeability (MP), proline and hydrogen peroxide (H₂O₂) accumulation, nonenzymatic antioxidant activity, and the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of 12 sunflower cultivars grown under drought conditions. Silicon applied to the soil counteracted the deleterious effects of drought in 6 of the 12 sunflower cultivars. In general, SR and H₂O₂, proline, and MDA content were increased in all the cultivars under drought stress. However, application of Si decreased their levels and alleviated membrane damage (MP) significantly by increasing leaf RWC. The CAT activity was significantly decreased by drought stress, but supplemental Si increased it. In general, SOD and APX activities of the cultivars were increased by drought and decreased by application of Si. The nonenzymatic antioxidant activity of the cultivars was significantly increased by Si under drought stress. Based on the present work, it can be concluded that applied Si alleviates drought stress in sunflower cultivars by preventing membrane damage, although the cultivars showed genotypic variation in response to applied Si.     

Effect of silicon on photosynthetic gas exchange,photosynthetic pigments,cell membrane stability and relative water content of different wheat cultivars under drought stress conditions

This study aims to explain the effects of silicon (Si) foliar application on gas exchange characteristics, photosynthetic pigments, membrane stability and leaf relative water content of different wheat cultivars in the field under drought stress conditions. The experiment was arranged as a split-split plot based on randomized complete block design with three replications. Irrigation regime (100%, 60%, and 40% F.C.), silicon (control and Si application) and wheat cultivars (Shiraz, Marvdasht, Chamran, and Sirvan) were considered as main, sub and sub-sub plots, respectively. This study was carried out at the Research Farm of the Collage of Agriculture, Shiraz University, Iran, during 2012–2013 growing season. The results showed that foliar application of silicon increased the leaf relative water content, photosynthesis pigments (chlorophyll a, b and total chl and carotenoids), chlorophyll stability index (CSI) and membrane stability index (MSI) in all wheat cultivars, especially in Sirvan and Chamran (drought tolerant cultivars), under both stress and non-stress conditions. However, more improvement was observed under drought stress as compared to the non-stress condition. In contrast, these parameters decreased under drought stress. Si significantly decreased electrolyte leakage in all four cultivars under drought stress conditions. Furthermore, the intercellular carbon dioxide (CO₂) concentration (C_i) increased under drought stress. Si application decreased C_i especially under drought stress conditions. Net photosynthesis rate (A), transpiration rate (E) and stomatal conductance (g_s) were significantly decreased under drought conditions. Under drought, Si applied plants showed significantly higher leaf photosynthesis rate, transpiration rate, and stomatal conductance. Intrinsic water use efficiency (WUEi) and carboxylation efficiency (C_E) decreased in all cultivars under drought stress. However, the silicon-applied plants had greater WUEi and C_E under drought stress. The stomatal limitation was found to be higher in stressed plants compared to the control. Exogenously applied silicon also decreased stomatal limitation. Overall, application of Si was found beneficial for improving drought tolerance of wheat plants.     

CONTRIBUTION OF PROLINE AND INORGANIC SOLUTES TO OSMOTIC ADJUSTMENT IN COTTON UNDER SALT STRESS

Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψ_w) and osmotic potential (Ψ_s)decreased in response to NaCl levels. Although Ψ_wand Ψ_s decreased during salt stress, pressure potential Ψ_p remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m^?3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na⁺ and Cl^?. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca²⁺ and Mg²⁺ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na⁺ and Cl^? accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars.     

Amelioration of Drought in Sorghum (Sorghum bicolor L.) by Silicon

The purpose of this study was to analyze the effects of silicon (Si) nutrition on sorghum growth under drought. The present study investigated the distribution of Si in plant parts under stress conditions and its effects on physiological and growth traits. The study was conducted during 2 years (2007–2009) at PMAS Arid Agriculture University, Rawalpindi, Pakistan. Polyethylene glycol (PEG) 6000 (–4.0, –6.0, –8.0, and –10.0 Mpa) solution was used to screen drought-tolerant (Johar1) and drought-susceptible (SPV462) sorghum (Sorghum bicolor L.) cultivars, which were replicated three times with Si sources of potassium silicate (K₂SiO₃) (Si₃₀₀: 300 ml L^?1) and control (Si₀) treatments. The results showed that drought-tolerant cultivars accumulated maximum Si under Si treatment versus Si absence, which resulted increased leaf water potential, leaf area index, Soil Plant Analysis Development (SPAD) chlorophyll, net assimilation, and relative growth rate over SPV462. Similarly, Si accumulation in leaves conserved transpiration and leaf water potential, verifying Si nutrition as a defense for plants under drought.     

Water relations and yield of wheat (Triticum aestivum L.) exposed to interactions of drought and fungal root diseases (Rhizoctonia and Pythium)

A pot experiment investigated the effects of root diseases (Pythium and Rhizoctonia) under drought conditions at either tillering or anthesis stages on the water-use efficiency (WUE), water relations, and yield components of wheat cultivars Janz and Mulgara. The pathogens reduced transpiration in Janz during drought at tillering and in both cultivars during the period of recovery after drought at anthesis. However, the pathogens did not affect WUE. WUE did not differ between well-watered plants and those droughted at tillering but it was reduced by 80% by drought at anthesis. Un-infected plants of cultivar Janz subjected to drought at tillering had a higher total water potential (Ψ_w) and osmotic potential (Ψ_s) than diseased plants. However, Ψ_s of un-inoculated plants that were droughted at anthesis was lower than diseased plants in the period following anthesis. Yield components were significantly higher in well-watered than droughted plants and higher in cv. Mulgara than cv. Janz. The pathogens affected transpiration during tillering, but not at later stages, when roots developed beyond the inoculation point. Although the pathogens caused damage to the roots, the effects on water relations parameters were minor. This suggests that wheat can tolerate moderate levels of these root diseases under drought.     

干旱处理下不同烤烟品系的生理差异研究

为培育抗性优良的烤烟品种,探究烤烟的耐旱特性及机理,以烤烟品系LY1306、中烟100和红花大金元为试验材料,研究在聚乙二醇6000(PEG-6000)模拟干旱胁迫和水分控制的干旱处理下,各烤烟品系叶片抗氧化酶类活性,丙二醛(MDA)和脯氨酸含量变化,以及光合生理特性和叶片细胞超微结构的差异。结果表明,25%PEG-6000胁迫下,LY1306能保持较好的生理状态,具有较高的SOD活性和较强的脯氨酸渗透调节能力;中烟100的个别叶片出现萎蔫,SOD活性较LY1306低,较对照组POD和CAT活性显著降低,MDA含量较高;红花大金元叶片出现严重萎蔫,CAT活性降低幅度最大,脯氨酸积累量较高。在反复缺水干旱条件下,LY1306能够维持较高的CAT活性,MDA积累量少,水分利用率较高,蒸腾速率较低,细胞中叶绿体数量和叶绿体形态维持正常。红花大金元的POD活性增长明显,脯氨酸含量显著增长,但MDA积累量较大,叶绿体变形且数量明显减少。中烟100的POD活性较高,脯氨酸积累量较大,叶绿体结构较完整。综上,LY1306在干旱胁迫下具有较强的清除活性氧和脯氨酸渗透调节能力,综合抗旱能力较好。本研究结果为培育抗旱烤烟品种提供了理论依据。     

Assessment of drought tolerance in mung bean cultivars/lines as depicted by the activities of germination enzymes,seedling’s antioxidative potential and nutrient acquisition

Drought stress hampers firm crop stand establishment and yield in arid and semiarid regions. The present study was conducted to examine the drought tolerance of various mung bean cultivars/lines based on the seed germination characteristics in relation with the seedling’s antioxidative potential and nutrient uptake. Activities of germination enzymes, seed germination attributes, seedling biomass production and nutrient uptake of studied cultivars/lines were adversely affected due to PEG-induced drought but the total soluble proteins (TSP) and malondialdehyde (MDA) contents were increased. The activities of catalse (CAT) and ascorbate peroxidase (APX) increased in all cultivars/lines being the maximum in cv./line NM-2006 and 8005. The activities of superoxide dismutase (SOD) and peroxidase (POD) were increased in cv./line NM-2006 and 8005 under drought condition. The ascorbic acid (AsA) and total phenolic content (TPC) decreased and total flavonoid content (TFC) increased in all cultivars/lines due to drought. Significant reduction in N, P, K, Ca and Mg was found in all cvs./lines but Fe remain unchanged. In conclusion, cultivars/lines NM-2006, 8005 were recommended as drought tolerant and 97,006 and 97,001 as drought sensitive ones. The study outcomes will likely be helpful for the farmers growing mung bean in rain fed areas for the better productivity.     

Foliar application of silicon at different growth stages alters growth and yield of selected wheat cultivars

To evaluate the response of some selected wheat cultivars to silicon application at different growth stages under drought stress, an experiment was carried out in the greenhouse of College of Agriculture, Shiraz University, Iran, during 2012 using a completely randomized factorial design with four replications. Experimental treatments included drought stress (100% F.C. as control and 40% F.C. as drought) and foliar application of 6 mM sodium silicate (control, application at mid tillering stage, at anthesis stage, and application at tillering + anthesis stages) and wheat cultivars (Sirvan and Chamran, relatively drought-tolerant, and Shiraz and Marvdasht, drought-sensitive cultivars). Drought stress significantly reduced chlorophyll content, leaf area, relative water content, grains per spike, 1000-grain weight, grain yield and biomass of all wheat cultivars. Furthermore, drought stress increased electrolyte leakage of the flag leaves of all cultivars. In contrast, foliar-applied silicon significantly increased these parameters and reduced electrolyte leakage. Furthermore, highest positive influence of silicon application was observed at combined use of silicon both at the tillering + anthesis stages in wheat plants under both stress and non-stress conditions. Significant differences were found in physiological responses among wheat cultivars. The drought tolerant cultivars (Sirvan and Chamran) had significantly higher growth and yield than those of drought sensitive cvs. Shiraz and Marvdasht under drought stress. In conclusion, foliar application of silicon especially at the tillering + anthesis stages was very effective in promoting resistance in wheat plants to drought conditions by maintaining cellular membrane integrity and relative water content, and increasing chlorophyll content.     

Morphological,Anatomical, and Physiological Assessment of Ramie [<Emphasis Type="Italic">Boehmeria Nivea</Emphasis> (L.) Gaud.] Tolerance to Soil Drought

Fiber yield is reduced when ramie [Boehmeria nivea (L.) Gaud.] is produced under drought stress. Responses in Leaf morphology, root development and stem anatomy, and physiology of six cultivars, varying in tolerance to drought stress, were measured to identify plant characteristics for adaptation to drought stress. Ramie plants, established from 10-cm sections of shoots, were grown in pots with soil. When plants were 60 cm tall (about 40 days), moisture content in the medium was maintained at 55% of water-holding capacity for 28 days by weighing the pots and sparingly watering. Medium was maintained at 80–85% of water-holding capacity for the control. Drought-tolerant cultivars of ramie had more fine hairs on abaxial leaf surfaces, produced thicker leaf cuticles, better preserved leaf shape, and erectness, lost fewer leaves. They also generated longer roots with larger root masses and more storage organs, preserved higher root-to-shoot ratios, produced larger diameter stem vessels, and better conserved cell integrity than drought-sensitive cultivars of ramie when plants were grown under drought stress. Fiber yield was better in drought tolerant cultivars of ramie, because these cultivars had adapted root systems, leaf responses, cellular responses, and biochemical activities to allow plants to continue higher levels of photosynthesis and carbon deposition under more stressful environments than the less drought tolerant cultivars. Cultivars ‘Huangketong’ and ‘Qingkezi’ were best adapted to drought tolerance in the study.     

Drought stress-induced oxidative stress and antioxidative responses in four wheat (Triticum aestivum L.) varieties

Drought stress was imposed on four varieties of wheat (Triticum aestivum L.), Mohan Wonder (MW), Kedar (K), Gayetri (GY) and Gandhari (GN), for 3, 6 and 9 days. The activities of all five tested antioxidative enzymes, peroxidase, ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase, were enhanced initially in varieties K and GN, whereas in MW and GY, catalase and superoxide dismutase showed a decrease in activity at all periods of drought stress. Peroxidase and glutathione reductase activities increased even on the ninth day of stress in K and GN, but all other activities showed a decrease after 3 days of stress. H₂O₂ accumulation increased with drought stress, but in K and GN there was decrease during prolonged drought stress. Lipid peroxidation increased significantly due to drought stress, which was higher in the case of MW and GY. Proline, phenol and ascorbate content increased with period of drought stress. Carotenoid accumulation also increased initially. Total chlorophylls showed a general decrease during drought stress. The results of this study indicate that two of the varieties, MW and GY, are susceptible to drought stress, whereas the other two, K and GN, are tolerant, with peroxidase and glutathione reductase being most important in conferring tolerance.     

Potassium deficiency impedes elevated carbon dioxide‐induced biomass enhancement in well watered or drought‐stressed bread wheat

Potassium (K) deficiency reduces photosynthesis and biomass production of crop plants and also renders them vulnerable to drought stress, whereas elevated carbon dioxide (CO₂) has a positive effect on photosynthesis and yield and ameliorates the adverse effects of drought stress. This study aimed to characterize the physiological responses of wheat (Triticum aestivum L.) stressed with K deficiency under elevated CO₂ and drought conditions. Increased biomass production caused by elevated CO₂ as a consequence of increased photosynthesis and water use efficiency was absent in young K‐deficient wheat plants. Shoot K concentration was negatively affected by elevated CO₂ particularly under K‐deficient conditions, whereas K content per plant was greatest in plants supplied with adequate K and adequate water. Specific leaf weight was increased as a consequence of carbohydrate accumulation in the source leaves of K‐deficient plants particularly under elevated CO₂ and drought stress. Potassium deficiency clearly impeded the impact of elevated CO₂ in both well watered as well as drought‐stressed plants. Adequate K fertilization is a prerequisite for efficient harvesting of atmospheric CO₂ through increased photosynthesis, decreased transpiration, and increased biomass production under changing atmospheric CO₂ and soil moisture conditions.     

Influence of Silicon on Sunflower Cultivars under Drought Stress,II: Essential and Nonessential Element Uptake determined by Polarized Energy Dispersive X‐ray Fluorescence

Abstract: There is no information regarding genotypic variation in essential and nonessential nutrient accumulation of sunflower grown under drought stress with the presence or absence of supplemental silicon (Si) despite the role of this element in improving growth of some cultivars under drought conditions. Accumulation of elements in sunflower cultivars might be important for the genetic improvement of the crop's response to drought. An experiment under controlled conditions was carried out to study the genotypic response of 12 sunflower (Helianthus annuus L.) cultivars to drought and Si and the relationship to the uptake of elements [phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), chloride (Cl), molybdenum (Mo), Si, sodium (Na), vanadium (V), aluminum (Al), strontium (Sr), rubidium (Rb), titanium (Ti), chromium (Cr), nickel (Ni), bromine (Br), and barium (Ba)]. This was determined by polarized energy‐dispersive X‐ray fluorescence (PEDXRF). It was observed that uptake of nutrient and nonessential elements by sunflower cultivars were differentiated in response to applied Si and drought stress. Drought stress decreased mineral uptake of all the cultivars, and generally, application of Si under drought stress significantly improved Si, K, S, Mg, Fe, Cu, Mn, Na, Cl, V, Al, Sr, Rb, Ti, Cr, and Ba uptake whereas Zn, Mo, Ni, and Br uptake were not affected.     

Silicon alleviates nickel toxicity in cotton seedlings through enhancing growth,photosynthesis, and suppressing Ni uptake and oxidative stress

Cotton (Gossypium hirsutum L.) is a well-known and economically most beneficial crop worldwide while nickel (Ni) toxicity is a widespread problem in crops grown on Ni-contaminated soils. We investigated the response of silicon (Si) in cotton under Ni stress with respect to growth, biomass, gas exchange attributes, enzymatic activities, and Ni uptake and accumulation. For this, plants were grown in hydroponics for 12 weeks with three levels of Ni (0, 50, and 100 µM) in the presence or absence of 1 mM Si. Results showed that Ni significantly reduced the plant growth, biomass, gas exchange attributes, and pigment contents while Si application mitigated these adverse effects under Ni stress. Nickel stress significantly decreased antioxidant enzymes’ activities while increased malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and electrolyte leakage (EC) in leaves and roots. The application of Si enhanced the activities of antioxidant enzymes and reduced MDA, H₂O₂, and EC in plants. Nickel application significantly increased Ni concentration and accumulation in leaf, stem, and roots while Si application significantly decreased Ni in these plant parts. The present study indicates that Si could improve cotton growth under Ni stress by lowering Ni uptake and reactive oxygen species (ROS) and by increasing antioxidant enzymes activities.     

Effects of drought on the accumulation and redistribution of cadmium in peanuts at different developmental stages

This study aimed to investigate the impact of water deficit on cadmium (Cd) accumulation in peanut plants during different developmental stages. Two contrasting peanut cultivars, Fenghua 1 (high-biomass cultivar) and Silihong (low-biomass cultivar), were grown in a Cd-contaminated arable soil under different water regimes. The two cultivars differed from each other in seed Cd concentrations. Fenghua 1 exhibited lower Cd concentrations in the seeds than Silihong, which is associated with root-to-shoot Cd translocation. Drought plays different roles in the translocation and redistribution of Cd in peanut plants during different developmental stages. At the seedling stage, drought decreased shoot Cd concentrations for both cultivars, whereas at the pod-filling and pod-ripened stages, drought increased shoot Cd concentrations. Similarly, drought stress reduced pod Cd concentrations at the pod-filling stages and increased at the pod-ripened stages. Seed Cd concentrations in mature plants were increased by drought for both cultivars. Seed Cd concentrations were negatively correlated with biomasses of shoots and pods, but positively correlated with Cd concentration in the shoots and pods. Increased seed Cd concentrations under drought stress might result from the concentration effects due to drought induced decrease of plant growth.     

不同烤烟品种幼苗形态结构及光合参数对 干旱胁迫响应机制的差异

为了比较不同烤烟品种的苗期耐旱性差异,选用河南烟区主栽烤烟品种‘豫烟6号’、‘豫烟10号’、‘豫烟12号’和‘中烟100’为供试材料,利用浓度为15%的聚乙二醇(PEG-6000)模拟中度干旱环境,研究不同烤烟品种幼苗生物量、根系形态、叶片气孔特征、叶绿体超微结构和光合参数等指标对干旱胁迫响应机制的差异。结果表明:(1)干旱刺激了幼苗根系生长,抑制了地上种幼苗根冠比均显著提高;‘豫烟6号’和‘豫烟12号’幼苗根系生物量、总根长、根系表面积和根系体积均显著增加,但根系平均直径与对照无显著性差异;而‘豫烟10号’和‘中烟100’根系形态指标增加幅度较小,仅有‘豫烟10号’根系表面积显著增加,而根系平均直径均显著下降。(2)干旱引起‘中烟100’叶片气孔总面积比对照显著增加,‘豫烟12号’仅有气孔长度比其对照增加显著。(3)干旱处理后,‘豫烟6号’和‘豫烟12号’叶绿体整体结构变化不大,而‘豫烟10号’和‘中烟100’中叶肉细胞叶绿体被膜分解,与细胞壁分离;其中‘中烟100’叶绿体平均长度、长宽比和面积均显著降低。(4)与对照相比,干旱组叶片光合作用被抑制,其中‘豫烟10号’和‘中烟100’叶片净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)均显著下降,而胞间CO2浓度(Ci)显著上升,说明干旱胁迫下烤烟光合速率下降是非气孔因素所致。(5)干旱胁迫后‘豫烟6号’和‘豫烟12号’叶片叶绿素总量显著增加,而‘豫烟10号’和‘中烟100’却呈下降趋势。结果表明,‘豫烟6号’和‘豫烟12号’是耐旱型品种,而‘豫烟10号’和‘中烟100’抗旱性较差,抗旱能力排序为‘豫烟6号’‘豫烟12号’‘豫烟10号’‘中烟100’。     

花后干旱胁迫对不同持绿型玉米叶片衰老的影响

[目的]探讨不同持绿型玉米抗旱的生理机制差异,为促进作物持绿性状的应用,指导作物抗旱改良工作提供理论依据。[方法]利用盆栽试验,以正常灌水为对照,对持绿型玉米自交系齐319和早衰型玉米自交系B73在开花后进行1周的干旱胁迫处理,测定与抗旱相关的生理生化指标及叶片衰老特性。[结果]在干旱胁迫下,与早衰型玉米B73相比,持绿型玉米齐319叶片POD和SOD活性均较高。齐319叶片过氧化物酶(POD)和超氧化物歧化酶(SOD)活性较对照分别增加了32.53%和18.84%,B73较对照分别增加了12.79%和10.82%。干旱胁迫使两玉米自交系的叶片丙二醛(MDA)含量较对照都有显著增加,齐319较对照增加了14.23%,B73较对照增加了37.43%。与对照相比,齐319叶片脯氨酸含量增加了57.95%,B73叶片脯氨酸含量增加了43.67%。且在干旱胁迫下,持绿型玉米齐319具有相对较高的净光合速率(P_n)、气孔导度(G_s)和蒸腾速率(T_r),绿叶面积、叶片保绿度、光合色素含量均高于早衰型玉米B73,而蛋白水解酶活性以及叶绿素水解酶活性均低于早衰型玉米B73。[结论]持绿型玉米齐319在干旱胁迫条件下表现出较强的抗旱性。     

SILICON MITIGATES ULTRAVIOLET-B RADIATION STRESS ON SOYBEAN BY ENHANCING CHLOROPHYLL AND PHOTOSYNTHESIS AND REDUCING TRANSPIRATION

The aim of this study was to investigate the potential of silicon (Si) for alleviating Ultraviolet-B (UV-B) radiation stress based on changes in biomass, physiological attributes and photosynthetic characteristics of two soybean (Glycine max L.) cultivars, Kenjiandou 43 (‘K 43’) and Zhonghuang 35 (‘ZH 35’). The cultivars were raised with and without Si in the greenhouse, and then subjected to ambient, ambient + 2.7 kJ m^?2d^?1and ambient + 5.4 kJ m^?2d^?1of UV-B radiation. Depending on cultivar, plants suffered severe growth limitations under UV-B radiation, but the application of Si alleviated the adverse effects on growth and development by increasing the stem length, net photosynthetic rate (P_N) and leaf chlorophyll content. Concurrently, it decreased the stomatal conductance (Sc) and intercellular carbon dioxide (CO₂) concentration (Ci). In response to the UV-B radiation stress, the antioxidant enzyme activities of superoxide dismutase (SOD) increased by 41.2–72.7%, peroxidases (POD) by 49.5–85.7%, malodialdehyde (MDA) by 6.7–20.4% and soluble protein by 4.2–7.6%. The overall results indicated that media treatment with Si might improve soybean growth under elevated UV-B radiation through positive changes in biomass and some physiological attributes that were dependent on cultivar.     

Drought stress tolerance and photoprotection in two varieties of olive tree

Abstract

The olive tree (Olea europaea L.) is adapted to tolerate severe drought and high irradiance levels. Relative electron transport rate (J), photosynthetic efficiency (in terms of F _v /F _m and Φ_PSII), photochemical (qP) and non-photochemical quenching (NPQ) were determined in 2-year old olive plants (cultivars ‘Coratina’ and ‘Biancolilla’) grown under two different light levels (exposed plants, EP, and shaded plants, SP) during a 21-day controlled water deficit. After reaching pre-dawn leaf water potentials of about -6.5 MPa, plants were rewatered for 23 days. During the experimental period, measurements of gas exchange and chlorophyll fluorescence were carried out to study the photosynthetic performance of olive plants. The effect of drought stress and high irradiance levels caused a reduction of gas exchange, J, Φ_PSII and F _v/F _m and this decrease was more marked in EP. Under drought stress, EP showed a higher degree of photoinhibition, a higher NPQ and a lower qP if compared to SP. Coratina was more sensitive to high light and drought stress and had a slower recovery during rewatering. The results confirm that photoprotection is an important factor that affects photosynthetic productivity in olive, and that the degree of this process varies between the cultivars. This information could give a more complete picture of the response of olive trees grown under stressful conditions of semi-arid environments, and could be important for the selection of drought-tolerant cultivars with a high productivity.     

限水灌溉下春季追氮方式对小麦旗叶光合和衰老特性的影响

限水条件下,等量氮不同施用方式对小麦旗叶光合和衰老特性的调控效应不同;不同抗旱性品种对施氮方式的响应也有所差异。与拔节初期1次施氮处理（SF）相比,拔节初期、挑旗期2次施氮处理（DF）增加了供试品种旗叶中后期的叶绿素含量（Chl）、可溶蛋白含量（SP）、RuBPCase活性、气孔导度（Gs）和光合速率（Pn）,延长了叶绿素含量缓降期（RSP）、光合速率高值持续期（PAD）,提高了叶源量（LSC）;使旗叶生长中后期的超氧化物歧化酶（SOD）活性和过氧化物酶（POD）活性增加,细胞的活性氧（O2-）含量和丙二醛（MDA）含量降低。与抗旱品种石麦12相比,DF处理对抗旱性中等的品种石新733的旗叶光合生理参数、光合功能高值持续期具有更大调控效应。DF处理使供试品种的千粒重、产量和水分利用效率增加,其中石麦12后两指标增幅达显著水平。表明在春季适宜施氮量范围内,在肥力中等偏下地力条件下,生育中后期（挑旗期）追施适量氮素,具有提高叶片的细胞保护酶活性、维持细胞的较强活性氧清除能力,改善限水条件下小麦旗叶光合碳同化能力、延缓旗叶衰老、促进子粒灌浆和提高水分利用效率的作用。     

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

Rising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.