The mechanisms of melatonin action in shielding photosynthesis during heat stress

Abstract

Abstract The escalating global climate shifts lead to several negative impacts, including a continuous increase in average temperatures, imposing significant consequences on plant physiology, biochemical dynamics, and molecular processes. Central to these ramifications is the process of photosynthesis, pivotal for carbohydrate synthesis and essential for sustaining growth amidst normal or stressful environmental conditions. Exposure to heat stress (HS) negatively affects the photosynthetic potential, primarily due to the increased synthesis of reactive oxygen species, disrupting the optimal functionality of the photosynthetic apparatus. Melatonin (MLT) has emerged as a multifaceted signaling molecule exhibiting promising capabilities in mitigating the adverse effects of abiotic stress including HS on plants. While a substantial body of literature addresses the enhancement of plant resilience to various environmental stresses using MLT, the present review specifically focuses on the impact of MLT on photosynthesis during HS. It emphasizes MLT’s role in regulating chlorophyll synthesis and degradation, regulating stomatal movement, safeguarding photosynthetic proteins, and sustaining the photosynthetic process under HS. This could be achieved by various mechanisms including enhancing the transcription of photosystem genes, activating antioxidant defenses, promoting the xanthophyll cycle, and modulating enzymes involved in photosynthesis and carbohydrate metabolism. Consequently, this review aims to enhance our understanding of how MLT mediates the protection of the photosynthesis process under HS, offering insights for the development of heat-tolerant crops.