5-aminolevulinic acid-mediated plant adaptive responses to abiotic stress.

5-aminolevulinic acid (ALA) modulates various defense systems in plants and confers abiotic stress tolerance. Enhancement of crop production is a challenge due to numerous abiotic stresses such as, salinity, drought, temperature, heavy metals, and UV. Plants often face one or more abiotic stresses in their life cycle because of the challenging growing environment which results in reduction of growth and yield. Diverse studies have been conducted to discern suitable mitigation strategies to enhance crop production by minimizing abiotic stress. Exogenous application of different plant growth regulators is a well-renowned approach to ameliorate adverse effects of abiotic stresses on crop plants. Among the numerous plant growth regulators, 5-aminolevulinic acid (ALA) is a novel plant growth regulator, also well-known to alleviate the injurious effects of abiotic stresses in plants. ALA enhances abiotic stress tolerance as well as growth and yield by regulating photosynthetic and antioxidant machineries and nutrient uptake in plants. However, the regulatory roles of ALA in plants under different stresses have not been studied and assembled systematically. Also, ALA-mediated abiotic stress tolerance mechanisms have not been fully elucidated yet. Therefore, this review discusses the role of ALA in crop growth enhancement as well as its ameliorative role in abiotic stress mitigation and also discusses the ALA-mediated abiotic stress tolerance mechanisms and its limitation and future promises for sustainable crop production.