The Role of Heat Acclimation in Thermotolerance of Chickpea Cultivars: Changes in Photochemical and Biochemical Responses

Abstract

This study was conducted to determine the effects of heat stress on the physiological and biochemical responses of chickpea (Cicer arietinum L.; Diyar and Küsmen-99) cultivars that are both heat acclimated and non-acclimated. The seedlings were grown in soil for 15 days and then exposed to heat stress (35 °C, 5 days) after heat acclimation (30 °C, 2 days) or non-acclimation (25 °C, 2 days). Chlorophyll a fluorescence (ChlF) measurements were analyzed using the JIP test. Heat acclimation had no significant effect on ChlF parameters. Seedlings exposed to higher temperatures by acclimation were more tolerant in terms of ChlF parameters and Diyar had a better photochemical activity of photosystem II (PSII). Heat stress resulted in a decrease in electron transport efficiency, quantum yield, photosynthetic performance, and driving force in both chickpea cultivars, while K-band, L-band, and quantum yield of dissipation increased, especially in the non-acclimated cultivars. Additionally, ion leakage (RLR), malondialdehyde (MDA) content, and H2O2 synthesis increased in the cultivars, while water content (RWC), chlorophyll (a + b) content, and carotenoid content of the cultivars decreased. On the other hand, the cultivars attempted to eliminate reactive oxygen species (ROS) by increasing the content of anthocyanins and flavonoids and the activity of antioxidant enzymes (SOD and POD) under heat stress. Heat acclimation alleviated the negative effects of heat stress on each cultivar’s water content, chlorophyll and carotenoid content, membrane damage, photosynthetic activity, and antioxidant defense systems. The results of this study showed that, by providing heat acclimation more effectively, Diyar was better able to cope with the biochemical and physiological alterations that could be resulted from heat stress.