Effect of water deficit stress on photosynthetic indices of three chickpea (Cicer arietinum L.) cultivars

Introduction The water stress-induced limitation on plant growth is mainly caused by reductions in plant carbon balance, which depends on the balance between photosynthesis and respiration. In order to evaluate the water stress tolerant cultivar, photosynthetic parameters were investigated in seedlings of flowering and podding stages of Adel, Azad and Karaj arable chickpeas. Materials and methods The experiment was conducted as a factorial based on a completely randomized design with three replications under controlled conditions in 1394 with the aim of evaluating the effect of drought stress on 5 levels of 20, 40, 60, 80 and 100% of crop capacity on the photosynthetic index of cultivars. Pea, Adel, Azad and Karaj were planted in 3 stages of seedling, flowering and podding. Total Chl Content (TChl): The chlorophyll index was determined using the Chlorophyll Content Meter (CCM-200 plus, USA). Maximum quantum yield of PSII photochemistry (Fv / Fm), was measured using chlorophyll fluorimeter (Pocket PEA, Hansatech, England). transpiration rate (E) ،net photosynthetic rate (PN) and intercellular CO2 concentration(Ci) were determined in fully expanded leaves using a portable infrared gas analyzer (KR8700 system, Korea) Statistical analyses were made by MASTAT-C. Means were compared using the Duncan’s multiple range test (p 0.05). Results and discussion Fv/Fm: Drought stress in seedling stage at levels of 20 and 40% of crop capacity resulted in a significant reduction of Fv/Fm ratio in all three cultivars compared to non stress conditions. Results showed that drought stress levels (20, 40 and 60% of crop capacity) in all three cultivars resulted in a significant reduction in the efficiency of photosystem II compared to 80 and 100% of crop capacity. Comparison of mean of data on interaction effects of cultivar and stress in podding stage showed that chickpea cultivars did not differ significantly in this stage of growth in different conditions of drought stress. Related studies showed that the reduction of the Fv/Fm ratio in drought stress conditions, which indicates a reduction in the efficiency of photosystem II, is due to the reduction of electron transfer from the photosystem II to the photosystem I. TChl: In the seedling stage, the results showed that the highest and lowest total chlorophyll index was allocated to Karaj cultivar under non stress condition and free cultivar under severe stress conditions. At flowering stage, the results showed that drought stress at all levels resulted in a significant reduction of this trait compared to non-stress level. In the podding stage, Karaj cultivar was superior to free cultivar at most drought stress levels (20, 60 and 100% crop capacity). Related studies showed a sharp drop in chlorophyll content in high levels of stress, can reduce transmission of the required minerals and water leaves through transpiration reduce the suction of the vessel is wood. Transpiration: The results showed that drought stress at all levels significantly decreased transpiration rates in the cultivars compared to non-stressed conditions. At flowering stage, a significant decrease in transpiration was observed in all levels of drought stress in all chickpea cultivars. Comparison of meanings in the podding stage was similar to that of flowering stage. Related studies have shown that plants reduce the transpiration by closing the stomata to counteract the drought stress in order to preserve leaf water and prevent it from wasting. Ci: The results showed that in seedling stage, drought stress at levels of 20 and 40% of crop capacity led to a significant reduction of CO2 in leaf cells compared to non stress conditions. In comparison with chickpea cultivars, in flowering and podding stage, Karaj cultivar had the highest amount of intracellular CO2 at all drought levels, which was significant at 20 and 80% of the capacity of this increase compared to the fair and free cultivars. Studies on the selection of susceptible and tolerant drought stress in plants have shown that reducing intracellular CO2 concentration due to the closure of leaf stomata and preventing the entry of CO2 into leaf mesophilic cells. Pn: Comparison of mean of data in flowering seedlings showed that the highest amount of pure photosynthesis in Karaj cultivar was under non stress condition. There was no significant difference between treatments in pod filling stage. The increase of pure photosynthesis in Karaj cultivar compared to two other cultivars (fair and free) indicates that there are mechanisms of tension compatibility in order to prevent the reduction of photosynthesis and tolerance of this variety to drought stress. Conclusions This study showed that drought stress in seedling, flowering and podding stages of Adel, Azad and Karaj chickpea cultivars resulted in a significant decrease in pure photosynthesis, transpiration, intracellular CO2, chlorophyll content and photosystem II performance. Although the Karaj cultivar, due to its superiority in most of the studied traits, is compared with the other two cultivars as drought stress tolerant to those two varieties.