كليدواژه :
اسيميلاسيون CO2 , عملكرد فتوسيستم ІІ , مقاومت روزنه اي , نخود
چكيده فارسي :
به منظور شناسايي شاخص‌هاي مؤثر در ميزان تحمل به تنش و حفظ رشد پس از تنش در ژنوتيپ‌هاي نخود، آزمايشي با يك ژنوتيپ كانديد متحمل به خشكي MCC392 و يك رقم معرفي‌شده به‌عنوان متحمل به خشكي بين‌المللي MCC877 و يك ژنوتيپ كانديد حساس به خشكي شامل MCC68 در دو تيمار تنش خشكي (25 درصد ظرفيت زراعي) و بدون تنش (ظرفيت زراعي) در اتاقك رشد در شرايط كنترل‌شده به‌صورت فاكتوريل در قالب طرح كاملاً تصادفي با چهار تكرار انجام شد. تنش به‌مدت 9روز در مرحله گلدهي اعمال گرديد و سپس گياهان به اندازه ظرفيت زراعي آبياري شدند. ميزان عملكرد فتوسيستم ІІ، اسيميلاسيون CO2، مقاومت روزنه‌اي، ضريب پايداري غشاء، تعرق، محتواي نسبي آب برگ، پتانسيل آب برگ و صفات مورفولوژيكي ريشه و اندام هوايي ژنوتيپ‌ها در مراحل قبل از اعمال تنش، 24 و 48 ساعت پس از تنش و سپس 24 ساعت پس از آبياري (ترميم) مورد سنجش و ارزيابي قرارگرفت. در بررسي ميزان بهبود رشد در مرحله ترميم مشخص شد كه ژنوتيپ متحمل MCC877، بيشترين ميزان كارآيي مصرف آب و كمترين ميزان تعرق را در مرحله ترميم نسبت به دو ژنوتيپ ديگر داشت. بر اساس اين نتايج مي توان گفت كه حفظ ضريب پايداري غشاء، كاهش تعرق و افزايش كارآيي مصرف آب در افزايش توانايي گياهان جهت مقابله با تنش و همچنين فراهم‌نمودن شرايط رشد گياه پس از اتمام تنش، نقش مؤثري خواهند داشت. علاوه برآن، ژنوتيپ‌هاي متحمل (MCC392 و MCC877) كه از كاهش شديد عملكرد فتوسنتزي در شرايط تنش جلوگيري نمودند و قادر به انجام اسيميلاسيون CO2 در حد مطلوب بودند، پس از اتمام تنش نيز از توانايي بالاتري جهت برگشت به شرايط رشد عادي برخوردار بودند.
چكيده لاتين :
Introduction
Chickpea is an important source of protein supply in human diet. Drought decreases the yield and has the potential for leading into a total crop failure. However, chickpea is known for its better drought tolerance when compared to most of the other cool season legumes. Furthermore, drought stress is one of the fundamental reasons for reducing the amount of growth and yield of chickpea. One of plant response to drought stress is change in photosynthetic efficiency and photosynthetic pigment content. Fv/Fm ratio is a parameter that determinate any damage to photosystems and possible photo inhibition. Photosynthetic pigments play important roles in harvesting light. Drought stress decreases CO2 assimilation rate and root growing index leading to reduction of yield. Under drought stress condition plants close their stomata to reduce water loss and retain relative water content. So decrease in internal CO2 concentration and net photosynthetic rate would occur. Reduced inhibition of CO2 assimilation rate under drought stress is so important for resistant chickpea genotypes. The effects of drought stress on membrane stability index, relative water content and leaf water potential have also been investigated in many studies. This study is designed to investigate effective traits regarding growth retain under drought stress and recovery stages in resistant and susceptible chickpea genotypes. In addition, the study aims at determining the role of physiological indexes in growth retaining in drought stressed chickpea plants.
Materials & Methods
In order to evaluate the effective traits regarding growth retain under drought stress and recovery stage in chickpea genotypes, an experiment was conducted in controlled conditions with two tolerant genotypes (MCC392 and MCC877) and one susceptible genotypes (MCC68) were grown under controlled (field capacity) and drought stress (25% field capacity) conditions in growth chamber under 12.5 hours photoperiod (21°C day/8°C night) for the first month and 13 hours, photoperiod (27°C day/12°C night) for the second month similar to normal field situations in chickpea growing region. Drought stress induced for 9 days in the flowering stage and then plants were watering up to field capacity (recovery stage). Water use efficiency (WUE), CO2 assimilation rate (A), transpiration rate (E), leaf water potential, chlorophyll fluorescence, membrane stability index (MSI), relative water content (RWC), stomatal resistance, and leaf, area, dry weight and volume of roots were investigated before drought stress, 24 hours and 48 hours after drought stress and recovery stages in investigated genotypes.
Results & Discussion
Drought stress significantly decreased CO2 assimilation rate, transpiration rate, and PSII photochemical efficiency (Fv/Fm), RWC and MSI in all genotypes. In the recovery stage, MCC877 genotype had the highest WUE and the lowest transpiration rate as compared to other genotypes. Also in this stage, MSI in all genotypes was lower than control plants. MCC68 genotype (susceptible genotype) had the lowest MSI in recovery stage as compared to drought stressed plant after 48 hours According to these results, MCC68 genotype (as a susceptible genotype) could not retain MSI under drought stress and recovery stage while in resistant genotypes (MCC392 and MCC877) there was no significant difference for MSI in recovery stage as compared to drought stressed plant after 48 hours. Water potential was higher in recovered plant as compared to drought stressed plant after 48 hours while control plant in recovery stage had lower water potential as compared to drought stressed plant. MCC392 (resistant genotype) and MCC68 (susceptible genotype) recovered genotypes had the highest and the lowest increasing in leaf water potential as compared to drought stressed plant after 48 hours. Higher water potential in chickpea genotypes is effective in increasing drought tolerance and growth retaining after drought. CO2 assimilation rate and water use efficiency was higher in resistant genotypes (MCC392 and MCC877) as compared to susceptible genotype (MCC68) in all drought stress stages. Resistant genotypes had lower transpiration rate under drought stress as compared to control plants in all investigated stages.
Conclusions
According to the results, higher membrane stability index, lower transpiration rate and higher water use efficiency can be effective in growth retain under drought stress and recovery stage. Also tolerant genotypes (MCC392 and MCC877) that have prevented the sharp decreased in photochemical efficiency and CO2 assimilation rate under drought stress had higher ability to growth retain after drought stress.
