Plant development and heat stress: role of exogenous nutrients and phytohormones in thermotolerance

Climate change has posed a significant threat to agricultural productivity in recent years. Due to their sessile nature, plants are vulnerable to various biotic and abiotic stresses. Heat stress has emerged as the most significant abiotic stress in recent years, as global temperatures rise daily. Heat stress inhibits photosynthesis, plant growth, pollen production, and reproduction. The plant's photosynthetic efficiency is mainly reduced by the overproduction of reactive oxygen species, denaturation of heat shock proteins, and alterations in several enzyme activities. Phytohormones have been shown to provide a comprehensive mechanism for stress resistance at numerous biochemical, molecular, and physiological levels, indicating that they play an essential role in plant growth and development. The various stressors primarily cause nutritional deficits and limit plant nutrient absorption. Phytohormones can enhance heat stress tolerance by boosting seed germination, antioxidant enzymes, leaf photosynthesis, seedling growth, and root growth while decreasing electrolyte leakage, reactive oxygen species, and malonaldehyde. At the same time, plant exogenous nutrients such as Ca, K, Mg, and N also engage in ROS scavenging activities by boosting antioxidant qualities, increasing photosynthetic potential, and decreasing cell membrane leakage by resynthesizing chlorophyll pigments. To cope with heat stress, plants have evolved adaptive systems. Plant defense responses to various abiotic challenges, including heat, are regulated by the classical plant hormones, which include auxin, cytokinin, abscisic acid, brassinosteroids, jasmonate, ethylene, and salicylic acid. These hormones integrate environmental stimuli and endogenous signals. Plants that receive exogenous administration of those hormones before or after heat stress are more thermotolerant. This review focused on the physiological, molecular and biochemical aspects that plants experience due to heat stress and the role of exogenous phytohormones and plant nutrients in mitigating heat stress.