Effect of peg-induced drought stress on seed germination and initial growth of three cucumber cultivars

Although drought and defoliation stress have been shown to reduce soybean [Glycine max (L.). Merr.] yield, little information has been published regarding their effects on soybean seed quality. Field experiments were conducted in 1986, 1987, and 1989 to evaluate the effect of drought and defoliation (1989 only) stress during soybean seed development on seed germination and vigor. Essex (MG [maturity group] V) and Union (MG III) were grown in 1986 and 1987, and Harper (MG III) and McCall (MG 00) in 1989. Moisture treatments were either well watered or drought stressed during seed development (R5 to R7). In 1989, a total defoliation treatment was also imposed at R6 as an additional stress factor. There were significant reductions in yield and yield components following drought stress in all 3 yr and following defoliation in 1989. Leaf conductance and transpiration also decreased in the drought stress treatments. There was no effect of drought stress on seed germination or seed vigor as measured by accelerated aging germination and the cold test across the four cultivars (determinate and indeterminate) and 3 yr. In 1989 slight changes in 3‐d germination and conductivity occurred for some drought stress treatments. Most of this response, however, was related to increased occurrence of hard seed, which does not represent an indication of a change in vigor. Seed germination and vigor were significantly reduced for small, flat, shriveled, and underdeveloped seeds that only occurred following defoliation. These seeds represented a small portion of the seed lot that would normally be removed during conditioning. The data suggest that drought stress would have no effect on seed germination or vigor, unless the stress was severe enough to produce shriveled, flat, underdeveloped seeds.

The individual and cumulative effects of drought stress (DS) and heat stress (HS) are the primary cause of grain yield (GY) reduction in a rainfed agricultural system. Crop failures due to DS and HS are predicted to increase in the coming years due to increasingly severe weather events. Plant available silicon (Si, H4SiO4) has been widely reported for its beneficial effects on plant development, productivity, and attenuating physiological and biochemical impairments caused by various abiotic stresses. The current study investigated the impact of pre-sowing Si treatment on six contrasting wheat cultivars (four drought and heat stress-tolerant and two drought and heat stress-susceptible) under individual and combined effects of drought and heat stress at an early grain-filling stage. DS, HS, and drought-heat combined stress (DHS) significantly (p < 0.05) altered morpho-physiological and biochemical attributes in susceptible and tolerant wheat cultivars. However, results showed that Si treatment significantly improved various stress-affected morpho-physiological and biochemical traits, including GY (>40%) and yield components. Si treatment significantly (p < 0.001) increased the reactive oxygen species (ROS) scavenging antioxidant activities at the cellular level, which is linked with higher abiotic stress tolerance in wheat. With Si treatment, osmolytes concentration increased significantly by >50% in tolerant and susceptible wheat cultivars. Similarly, computational water stress indices (canopy temperature, crop water stress index, and canopy temperature depression) also improved with Si treatment under DS, HS, and DHS in susceptible and tolerant wheat cultivars. The study concludes that Si treatment has the potential to mitigate the detrimental effects of individual and combined stress of DS, HS, and DHS at an early grain-filling stage in susceptible and tolerant wheat cultivars in a controlled environment. These findings also provide a foundation for future research to investigate Si-induced tolerance mechanisms in susceptible and tolerant wheat cultivars at the molecular level.

In order to evaluate the effect of seed treatment with glycinebetaine, a factorial experiment with 5 glycinebetaine levels (0, 2, 4, 8 and 16 mM) and 6 drought stress levels (0, -0.1, -0.2, -0.4, -0.8 and -1 MPa) was conducted based on completely randomized design with 3 replications. Corn seeds were immersed in water for 24 hours at corresponding glycinebetaine concentrations. These seeds were placed in petri dish and were exposed to different drought stress levels using PEG 6000. Results showed that drought stress caused a significant reduction in all measured parameters at different glycinebetaine concentrations. However, glycinebetaine concentrations of 2 and 4 mM effectively decreased the drought stress impact on seeds. Seed treatment with glycinebetaine, however, could not alleviate the effect of drought stress on germination rate. The three-parameter logistic model fitted to germination percentage effectively successfully justified the advantageous effect of seed treatment with glycinebetaine under drought stress. According to the model estimation, the drought level which causes 50% reduction in germinability was happened at higher drought stress levels when seeds were treated with glycinebetaine. Seed treating with glycinebetaine could alleviate the effect of drought stress on germination percentage, radicle and coleoptile length and fresh weight. Nevertheless, increasing the glycinebetaine concentration above 8 mM negatively affected germination and related parameters. Keywords: Glycinebetaine, Germination percentage, Coleoptile length, Radicle length, Corn

خار مریم یا ماریتیغال (Silybum marianum L.) گیاهی دارویی، علفی و یک‌ساله است که برای درمان بیماری‌های کبدی استفاده می‌شود. به منظور بررسی اثر تنش خشکی و کودهای زیستی بر خصوصیات کمی و کیفی ماریتیغال‌، آزمایشی به صورت کرت‌های خرد شده در قالب طرح بلوک-های کامل تصادفی در سه تکرار در مزرعه تحقیقاتی دانشگاه زابل در سال زراعی 92-1391 اجرا شد. کرت‌های اصلی شامل آبیاری با 50، 70 و 90 درصد ظرفیت زراعی و کرت‌های فرعی شامل تغذیه گیاه با کودهای زیستی نیتروکسین، سوپرنیتروپلاس، فسفات بارور 2، میکوریزا به صورت بذر مال و عدم مصرف کود بود. صفات مورد مطالعه شامل عملکرد دانه، تعداد کاپیتول در بوته، تعداد دانه در کاپیتول، وزن هزار دانه، درصد اسانس، درصد ماده آلی گیاه، درصد پرولین و درصد پروتئین دانه بودند. نتایج نشان داد که اثر تنش خشکی، کود زیستی و برهمکنش آن‌ها بر کلیه صفات مورد بررسی در سطح احتمال یک درصد معنی‌دار شد. بیشترین عملکرد دانه (00/1300 گیلوگرم)، تعداد کاپیتول در بوته (00/12 عدد)، وزن هزار دانه (27/23 گرم)، درصد ماده آلی گیاه (00/95 درصد) و درصد پروتئین دانه (19/17 درصد) در تیمار 90 درصد آبیاری و کود زیستی نیتروکسین حاصل شد. حداکثر تعداد دانه در کاپیتول با 67/87 عدد به تیمار 90 درصد آبیاری و کود زیستی میکوریزا تعلق داشت. تیمار‌های 70 و 90 درصد آبیاری و کود زیستی نیتروکسین به ترتیب حداکثر و حداقل صفات درصد اسانس (72/3 درصد) و درصد پرولین (04/0 درصد) را تبیین نمودند. تعداد کاپیتول در بوته مهم‌ترین جزء تعیین‌کننده عملکرد بود. کود زیستی نیتروکسین نسبت به سایر کودها توانست تنش خشکی را بیشتر تعدیل نماید و موجب بهبود ویژگی‌های کمی و کیفی گیاه ماریتیغال شود. بنابراین، به نظر می‌رسد که در راستای نیل به اهداف کشاورزی پایدار به جای کودهای شیمیایی قابل توصیه ‌باشد.

Heat and drought priming induce tolerance to subsequent heat and drought stress by regulating leaf photosynthesis, root morphology, and antioxidant defense in maize seedlings

Differential variations in total flavonoid content and antioxidant enzymes activities in pea under different salt and drought stresses

Aim. Screening for complex heat and drought resistance in varieties of soybeans that differ for maturity in growing experiences and in vitro culture. Methods. To create the conditions of "artificial drought" experimental seedlings and calluses with the addition of 10% mannitol solution were cultured, heat resistance analysis out under the influence of temperature shock (60 ° C) of different duration (10-30 minutes) was carried. Drought and heat resistance by rapid analysis of seed germination and growth inhibition were determined, and in vitro by growth index (RI) and protein coagulation temperature (PCT). Results. During drought and hyperthermia tested varieties with different ripening differ in the degree of resistance to these stressors. Increased drought and heat resistance in conditions, both in vivo and in vitro middle-matured Yatran and middle-early Ustya, lowered – ultra-ripe Anushka were showed. The ripening Hajibey variety the lowest level of complex drought and heat resistance was characterized. Conclusions. It is assumed that the level of drought and heat resistance is determined by the genotypic characteristics of the varieties and may be related to the sign of the duration of the growing season – rapidity of maturity. Keywords: Glycine max (L.) Merr., duration of growing season, drought resistance, heat resistance, callus culture.

The effects of drought stress on root morphology, endogenous hormones, chlorophyll fluorescence and active oxygen metabolism in three different stages of sweet potato rooting, branching and tubering stage were studied by sand culture method with 10% PEG-6000 simulating drought stress. The results showed that the biomass of sweet potato decreased significantly under drought stress in different periods, with the degree of drought stress being 10 days > 20 days > 30 days after transplantation. Drought stress significantly reduced the average diameter and root volume at the 10 days after transplantation, followed by the 20 days and 30 days. Both the main and interactive effects of different periods and drought stress significantly affected root morphological characteristics. Drought stress at different stages significantly reduced chlorophyll fluorescence characteristics, resulting in blocked photosynthate formation, and inhibited root differentiation. Drought stress affected the proportion of endogenous hormones in root (with decreases of indoleacetic acid and zeatin riboside contents but increases of abscisic acid contents) and thus inhibiting root differentiation of sweet potato. The earlier the stress time, the more serious the root differentiation of sweet potato was hindered. Across different drought-tolerant varieties, the severity of root differentiation blocked in Jishu 26 was significantly lower than that in Guangshu 87. Root endogenous hormones and chlorophyll fluorescence were the key drivers for the average diameter and root volume (R1=0.936, R2=0.972). Zeatin riboside, maximal photochemical efficiency, and abscisic acid had greater direct effects on average diameter and root volume of sweet potato. Sweet potato was more sensitive to drought stress in the 10th day after transplanting. Therefore, proper irrigation should be considered in case of drought in seedling stage of sweet potato.

Rapid cycling brassica (RCB) plants, because of their short life cycle and ease of growth under laboratory conditions, offer a valuable tool for studying Brassica nutrition. We have been particularly interested in B nutrition in Brassica and, therefore, a hydroponic system was developed to accurately deliver micronutrient concentrations to RCB plants. RCB plants were supported in predrilled holes in the lids of brown 1-L plastic containers. Nutrients were supplied by spraying a modified Hoagland's solution onto the plant roots as they developed inside the containers. This system provided adequate solution aeration for plant growth and allowed analysis of both plant shoots and roots. RCB seeds were pregerminated for radicle emergence, then placed in the holes in the plastic container lids. The effect of B nutrient concentration on B uptake was examined using nutrient solutions containing 0.08, 0.02 and 0.00 ppm added B. Leaf B contents were 139.5, 26.1, and 7.1 g·g–1 for plants grown in 0.08, 0.02 and 0.00 ppm added B, respectively. Effects of drought stress on B uptake and distribution were studied by adjusting nutrient solution osmotic potential using polyethylene glycol (PEG) 8000. PEG-induced drought, (osmotic potential –0.1 MPa) reduced leaf and root B content ≈50% compared to plants grown in nutrient solution only (–0.05 MPa). Boron content in the shoots and pods, however, was not affected by PEG-induced drought stress. These results suggest that this system provides a reliable tool for studying nutrition and drought stress effects using RCB plants.

Amaç: Bu çalışma, Lolium perenne çeşitlerinin fide gelişim aşamalarında tuz ve kuraklık stresine tepkisini belirlemek amacıyla yapılmıştır.Yöntem ve Bulgular: Tohum materyali olarak dört çok yıllık çim çeşidi (Apple GL, Ecologic, Barminton ve Solstice II) kullanılmıştır. Lolium perenne çeşitlerinde fide gelişim aşamalarında tuz (0, 50, 100, 150 ve 200 mM NaCl) ve kuraklık (0, -0.4, -0.8, -1.2. ve -1.6 MPa, PEG-6000) stresi oluşturmak için beş farklı dozda sodyum klorür ve polietilen glikol kullanılmıştır. Fide gelişimi denemeleri tesadüf parselleri deneme deseninde faktöriyel düzende 4 tekrarlamalı olarak yürütülmüştür. Lolium Perenne çeşitlerinin fide gelişimi, tuz ve kuraklık stresine toleransları araştırılmıştır. Araştırma sonucunda tuz uygulamasında fide kök uzunluğu hariç tüm özelliklerde çeşit, tuz stresi ve çeşit x tuz stresi interaksiyonların önemli olduğu belirlenmiştir. Kuraklık uygulamasında fide kök uzunluğu ve fide sap uzunluğu hariç tüm özelliklerde çeşit x PEG interaksiyonların önemli olduğu belirlenmiştir. Genellikle tuz ve kuraklık stresi arttıkça incelenen özelliklerde önemli azalma olduğu ortaya konmuştur.Genel Yorum: Lolium perenne çeşitlerinin fide gelişimi incelenen özelliklere göre, farklı oranda tepkiler vermiştir. Tuz’un ve PEG-6000'in Lolium perenne fide gelişiminde kuraklık stresi yaratmada yararlı bir ajan olduğu sonucuna varılabilir, ancak Lolium perenne tuz ve kuraklık stres toleransını daha iyi belirlemek için (150 mM )tuz ve (-1.2 MPa)'dan daha düşük ozmotik potansiyeller uygulanmalıdır. Çalışmanın Önemi ve Etkisi: Küresel ısınmanın etkilerini giderek hissedildiği günümüzde kuraklık sorunu ve alternatif su kaynaklarının kullanımına toleranslı tür ve çeşitlerin belirlenmesi çok önemli olacaktır. Kuraklık ve tuzluluk problemine toleranslı tür ve çeşitlerin kısa dönemde belirlenmesi de ayrıca önem taşımaktadır. 21 gün gibi kısa bir çalışma süreci ile yeşil alanlarda kullanılabilecek çeşitlerin test edilmesi tuzluluğa veya kurağa dayanıklı ya da toleranslı çeşidin belirlenmesi çim alanların sürdürülebilirliği açısından önem arz etmektedir.

In order to evaluate the effects of drought stress and defoliation on sunflower, a study was conducted under controlled conditions. Treatments were a combination of three levels of drought ((100, 60 and 30 percent of Field Capacity (FC)) and three levels of defoliation (control, removal of either 4 or 6 leaves from lower part of the plant) laid out, in a Completely Randomized Design with four replications. Drought stress was applied from 4-leaf- stage up to the end of plant growth period while leaf removal was conducted at the heading stage. Results indicated that drought stress affected most of the measured parameters. Plant height, plant dry matter, stem diameter, head size, seed number/head, 100-seed weight and seed weight/ head declined upon drought stress as compared to control. SPAD readings increased as drought stress increased. Defoliation caused an increase in SPAD and a decrease in seed number/head. Leaf number was not affected by either drought or defoliation. Keywords: Defoliation; Drought stress; Plant height; Seed weight; Sunflower

ABSTRACTThe effects of silicon (Si) and salicylic acid (SA) applications on proline content and expression of Δ1-pyrrolin-5-carboxylate synthetase (P5CS) were examined under different drought levels and different drought exposure times. Two wheat cultivars, a drought tolerant and a drought sensitive were used. The experiment was a factorial based on completely randomized design with three replicates. Expression analysis by the quantitative real time PCR showed that the tolerant cultivar had significantly higher P5CS expressions compared to the sensitive one under drought stress. In sampling time points, the maximum level of mRNA was observed at 48 h after stress was applied. At 48 h after stress induction, the expression of P5CS was almost 3.1 fold higher in the tolerant cultivar compared to the sensitive one. In both cultivars, gene expression decreased from 48 to 72 h. The stressed plants treated with Si + SA showed a higher expression. Proline content started to increase by Si and SA treatments and the maximum proline content was obtained at simultaneous application of Si + SA. Drought stress significantly reduced chlorophyll content, relative water content and leaf water potential of both cultivars, while increased electrolyte leakage (EL) of the leaves. In contrast, foliar-applied Si and SA significantly increased these parameters and reduced EL, and the effect of simultaneous application of Si and SA was greater. The results suggest that the P5CS is a stress inducible gene. This gene has the potential to be used for improvement of drought stress tolerance in wheat. Network analysis highlighted positive interaction of osmotic stress, drought and cold stress on P5CS1 and the regulatory role of MYB2, ERF-1, and EIN3 transcription factors. In conclusion, alleviation of drought stress by application of Si and SA was associated partially with enhanced expression of P5CS gene and following proline accumulation.

Molecular studies have shown that several genes with various functions are induced by drought stress and various transcription factors are involved in the regulation of the stress-inducible genes. To evaluate the effects of drought stress on gene expression, CRTBF2, DREB6 and DBF transcription factors as well as the expression pattern of Acyl, SuT5 and SuT4 genes were studied using qRT-PCR. The experiment was carried out as factorial based on completely randomized design. One factor included drought stress levels of -1, -2, -4 and -6 bar imposed by polyethylene glycol plus a control. The second factor consisted of four wheat cultivars as follows: Qaboos and Koohdasht (as drought tolerant), and Ehsan and Morvarid (as drought sensitive). Assessing the seedling morphological traits, such as germination percentage, plumule length and radicle length showed that with an increase in drought stress, the tolerant cultivars of Qaboos and Koohdasht showed lower decrease for these traits compared to the sensitive cultivars of Ehsan and Morvarid. The results of evaluating the gene expressions demonstrated that the DREB6 gene expression was higher in the tolerant cultivars of Qaboos and Koohdasht as compared to the sensitive cultivars of Ehsan and Morvarid, indicating the possible role of the product of this gene, as a transcription factor, in inducing promoters of drought tolerance genes and transcribing such genes. However, the CRTBF2 and DBF genes acted as repressor transcription factors in expressing the genes involved in the drought stress tolerance in the cultivars under study. The expressions of the Acyl and SuT5 genes were greater in the tolerant cultivars compared to the sensitive cultivars. The SuT4 gene expression was lower in both tolerant and sensitive cultivars than the expression of this gene in the corresponding control treatment. Therefore, it seems that the Acyl and SuT5 genes, through lipid decomposition and carbohydrate transport pathways, respectively, increased the tolerance of Qaboos and Koohdasht cultivars in this study.

IntroductionPterocarya fraxinifolia (Poiret) Spach (Caucasian wingnut, Juglandaceae) is a relict tree species, and little is known about its tolerance to abiotic stress factors, including drought stress and heavy metal toxicity. In addition, salicylic acid (SA) has been shown to have a pivotal role in plant responses to biotic and abiotic stresses.MethodsThe current study is focused on evaluating the impact of foliar application of SA in mediating Caucasian wingnut physiological and biochemical responses, including growth, relative water content (RWC), osmotic potential (Ψs), quantum yield (Fv/Fm), electrolyte leakage, lipid peroxidation, hydrogen peroxide, and antioxidant enzymes, to cadmium (Cd; 100 µM) and drought stress, as well as their interaction. Moreover, the antioxidant activity (e.g., ascorbate peroxidase, catalase, glutathione reductase, peroxidase, and superoxide dismutase activities) of the stressed trees was investigated. The study was conducted on 6-month-old seedlings under controlled environmental conditions in a greenhouse for 3 weeks.Results and discussionLeaf length, RWC, Ψs, and Fv/Fm were decreased under all treatments, although the effect of drought stress was the most pronounced. An efficient antioxidant defense mechanism was detected in Caucasian wingnut. Moreover, SA-treated Caucasian wingnut plants had lower lipid peroxidation, as one of the indicators of oxidative stress, when compared to non-SA-treated groups, suggesting the tolerance of this plant to Cd stress, drought stress, and their combination. Cadmium and drought stress also changed the ion concentrations in Caucasian wingnut, causing excessive accumulation of Cd in leaves. These results highlight the beneficial function of SA in reducing the negative effects of Cd and drought stress on Caucasian wingnut plants.

گیاهان مرتعی از اهمیت و نقش ویژه ای در صنایع دارویی برخوردارند. کاهش کمی و کیفی منابع آب همراه با شوری خاک از مهمترین عوامل بازدارنده در تکثیر و رشد گیاهان بشمار می رود. لذا این امر نیازمند شناخت و بررسی شرایط مطلوب رشد گیاهان می‌باشد. زیره سیاه (Bunium persicum Boiss) یکی از گیاهان مهم دارویی ایران است که دارای خواص ضد نفخ، مقوی معده، اشتهاآور و مدر بودن می باشد. تنش‌های شوری و خشکی از عوامل مهم کاهش عملکرد این گیاه محسوب می‌شود. به‌‌منظور بررسی تأثیر تنش‌های شوری و خشکی دو آزمایش به‌‌صورت مجزا در قالب طرح کاملاً تصادفی با چهار تکرار بر روی بذر گونه زیره سیاه انجام شد. تنش خشکی شامل پنج سطح (شاهد، 2/0- ، 4/0- ، 6/0- و 8/0-) مگاپاسکال ایجاد شده توسط محلول پلی‌اتیلن‌گلیکول 6000 و تنش شوری نیز در شش سطح (شاهد، 50، 100، 150، 200 و dS.m-1300) اعمال شد. بعد از اعمال تیمارها شمارش بذور جوانه‌زده به‌صورت روزانه انجام شد و درصد و سرعت جوانه‌زنی، طول ریشه‌چه، ساقه‌چه و گیاه‌چه و نیز ضریب آلومتری و بنیه بذر تعیین گردید. نتایج آنالیز آماری نشان داد که تنش‌های خشکی و شوری، درصد و سرعت جوانه‌زنی، شاخص بنیه‌ی بذر، ضریب آلومتری، طول ساقه‌چه، ریشه‌چه و گیاه‌چه را به‌طور معنی‌داری کاهش می‌دهند، به‌طوری‌که جوانه‌زنی در تیمار 06/- مگاپاسکال خشکی به‌طور کامل متوقف شد. داده‌های تحقیق نشان می‌دهد که زیره سیاه گونه‌ای حساس نسبت به تنش‌های محیطی از جمله خشکی و شوری در مراحل ابتدایی جوانه‌زنی و رشد بذور می‌باشد.