Physiological changes of sweet and hot peppers in vegetative and reproductive growth stages treated by Ca and H2O2 under unforeseen heat stresses

High ambient temperature has adverse effects on plant vegetative and reproductive development and reduces crop yield. This experiment was designed to better understand the effects of unforeseen heat stresses on reproductive and vegetative growth of two species of pepper, and to find out whether or not Ca and hydrogen peroxide (H2O2) have any significant effects on the levels of heat tolerance as well as on the reproductive and vegetative traits of the peppers. Two species of hot and sweet peppers, exposed to exogenous H2O2 and CaCl2, were subject to the high temperature (40° ±2C). Both species showed higher stress indices, including MDA, H2O2, electrolyte leakage, antioxidant capacity, phenol content, and chlorophyll fluorescence under heat stresses. Moreover, the given parameters were greater in the reproductive stage compared with the vegetative stage. Also, sweet peppers absorbed greater amounts of Ca in comparison with the hot peppers under stress conditions. The dominant fatty acid of the pepper leaves was found to be linolenic acid in all conditions. Under heat stresses, the saturate/unsaturated ratio of the fatty acid changed. This ratio increased in the hot pepper and conversely, decreased in the sweet pepper. On the other hand, a decrease in the levels of glucose and fructose was observed under heat stresses, while hydrogen peroxide significantly increased the two sugars. Nonetheless, the changes observed were greater in the sweet pepper in comparison with the hot pepper. All in all, it seems that, under the treatment, on the one hand, the fatty acids and existing sugars due to applying hydrogen peroxide, and on the other hand, the biochemical defense system of the peppers increased due to the presence of Ca, increasing its heat tolerance.