Effect of Heat Stress on Photosystem II, Antioxidant Activity and Micronutrient Concentration in Contrasting Cultivars of Greengram (Vigna radiata (L.) Wilczek)

Abstract

Heat stress around flowering has negative effect on greengram (Vigna radiata (L.) Wilczek) grain yield. The pot culture experiments were conducted to study the response of antioxidant system, photosystem II and micronutrient concentration to above-optimum temperature at flowering stage in two cultivars of greengram (Vigna radiata (L.) Wilczek) cv. SAMRAT (heat tolerant) and VBN-2 (heat susceptible). The plants were grown under natural light and atmospheric conditions (33/22°C day/night) up to the first appearance of flower. Then, cohort of plants were: (a) exposed to natural environment (33/22°C day/night) for 13 days and were (b) exposed to controlled environment 33/22 to 45/30°C (day/night) for 13 days by gradually increasing 1°C per day in day/night temperature and then pots were shifted to natural environment for 5 days for recovery. The activity of antioxidant enzyme (SOD, CAT and APX) were increased significantly as the temperatures increased upto 38/26°C in both cultivars and showed less reduction appropriately at 45/30°C in SAMRAT compared to VBN-2. It is possible that better tolerant to heat stress of SAMRAT was related to its ability to maintain higher levels of activity of antioxidant enzymes in all the temperature regimes. Quantum yield (Fv/Fm) showed significant reduction at 41/28°C in VBN-2 while at 45/30°C in SAMRAT indicating relative tolerance to heat stress. Micronutrient composition was not affected at 45/30°C except Cu content in leaves and Mn and Fe content in shoots. Upon heat stress treatment SAMRAT showed relatively less reduction of micronutrients like Cu, Mn and Fe content in leaves compared to VBN-2. The tolerant cultivar SAMRAT can serve as parents for breeding for heat stress tolerant variety.