A Review of Abscisic Acid and Proline-mediated Regulatory Mechanisms in Plant Temperature Stress Tolerance: Molecular, Biochemical and Physiological Insights

Temperature stress, including both high and low temperatures, has become a major constraint to global agricultural productivity under changing climatic conditions. Increasing temperatures and frequent heat waves adversely affect physiological and biochemical processes in crops such as Indian mustard, leading to reduced photosynthesis, membrane instability, oxidative damage, and ultimately lower yield. Temperature stress also increases reactive oxygen species (ROS) production, which disrupts cellular homeostasis, accelerates reproductive failure, and reduces biomass and oil yield. Abscisic acid (ABA) plays a central role in regulating plant responses to temperature stress by linking environmental signals with physiological and molecular mechanisms. Stress-induced ABA biosynthesis, particularly through activation of the NCED enzyme, initiates the PYR/PYL–PP2C–SnRK2 signalling pathway, leading to the expression of stress-responsive genes. ABA regulates stomatal closure, enhances antioxidant defence systems, and maintains osmotic balance under adverse temperature conditions. Proline, an important compatible osmolyte, also contributes significantly to stress tolerance. It protects cellular structures, stabilizes proteins and membranes, and scavenges reactive oxygen species generated during stress. Increased proline accumulation has been frequently associated with thermo-tolerant genotypes, contributing to improved membrane stability and enhanced recovery after stress exposure. Recent studies suggest a close interaction between ABA signaling and proline metabolism. ABA-mediated pathways stimulate proline biosynthesis and suppress its degradation, creating a regulatory network that helps maintain redox balance and cellular stability under temperature stress. The literature used in this review was systematically collected from major scientific databases, including Web of Science, Scopus, Google Scholar, and PubMed, using relevant keywords related to ABA, proline metabolism, and temperature stress. Selected peer-reviewed studies were screened for relevance, and only those providing molecular, physiological, and biochemical insights into ABA–proline interactions under temperature stress were included.