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• CA treatment induced plant physiochemical responses that enhance cold tolerance. • The efficacy of exogenous ABA in mitigating CS is strongly genotype-dependent. • ABA enhanced growth-related traits and antioxidant enzymes in CA and CS conditions. • ABA modulates physio-biochemical indices and stress-responsive gene expression under CS condition. Cold stress is a major constraint to rice ( Oryza sativa L.) production worldwide. Abscisic acid (ABA) is one of the key phytohormones involved in plant stress response. However, how ABA and chilling acclimation improve cold stress tolerance in rice is poorly understood. This investigation aimed to assess the impact of exogenous ABA application on morpho-physiochemical responses of rice genotypes under cold stress (CS) and chilling acclimation (CA) conditions. CS significantly diminished survival rates and seedlings growth in all genotypes, while significant variations were observed in their response to ABA application under CS and CA conditions. Moreover, ABA application displayed growth-promoting еffеcts and increased survival rates with higher ABA concentrations. Besides, it improved osmotic adjustment by osmolytes, which reduced MDA content and regulated osmotic and water balance, indicating a decrease in membrane lipid peroxidation. Furthermore, exogenous ABA application elevated ROS scavenging through regulating antioxidant enzyme activities and reduced the accumulation of H 2 O 2 and O 2 − , which enhanced dеfеnsе mechanisms of seedlings under CS and CA conditions. Moreover, 50 µM of ABA led to upregulated OsABF1, OsPsbR1 , and OsPsbR3 , while the OsABA45 gene was non-significantly affected under CS conditions. Besides, a slight downregulation was observed with OsABA45 in 9311; OsSNAC1 , and OsRAB16A in NIP under CA versus control. Notably, ABA application regulated the expression of key stress-responsive genes, including upregulation of the protective protein-coding gene (OsLEA3), while downregulation of the primary transcription factor ( OsDREB2A ) under CS conditions, indicating a complex, fine-tuned regulatory network. The current study highlights that modulating ABA signaling pathways can enhance cold tolerance by improving the antioxidant defense system, thereby providing a promising strategy to improve rice seedling survival under low-temperature stress.
Khatab et al. (Wed,) studied this question.