Comparative responses of rice (Oryza sativa L.) to iron toxicity, drought and salinity stress: Morphological, physiological, biochemical and molecular regulation mechanisms

Rice (Oryza sativa L.) is one of the world’s most important staple crops, ensuring food security for more than half of the global population. However, rice productivity is increasingly threatened by major abiotic stresses, particularly drought stress, salinity stress, and iron toxicity, whose severity is intensified by climate change and soil degradation. This review provides a comparative analysis of the morphological, physiological, biochemical, and molecular responses of rice to these constraints. Although these stresses arise from distinct environmental conditions, they converge toward common physiological disturbances, including growth inhibition, impaired photosynthesis, altered water relations, and excessive accumulation of reactive oxygen species (ROS). Drought stress mainly induces water deficit and stomatal closure, whereas salinity stress combines osmotic stress with ionic toxicity caused by excessive Na⁺ accumulation. In contrast, iron toxicity is characterized by excessive Fe²⁺ accumulation and enhanced ROS production through Fenton reactions. To maintain redox regulation and cellular homeostasis, rice activates antioxidant systems involving superoxide dismutase, catalase, ascorbate peroxidase, and the ascorbate-glutathione cycle. However, these defenses are often insufficient under severe iron toxicity because of the high reactivity of redox-active iron. At the molecular level, drought and salinity responses are largely regulated through ABA-dependent pathways and transcription factors such as OsDREB, OsNAC, and OsbZIP, whereas iron toxicity specifically mobilizes genes involved in iron uptake, transport, sequestration, and detoxification. This review highlights both the convergence and specificity of stress-response mechanisms and emphasizes the integration of redox regulation, antioxidant systems, ion homeostasis, and molecular responses into breeding strategies for developing multi-stress tolerant rice varieties.