ABA seed priming alleviates low-temperature-induced inhibition

Abscisic acid (ABA) is a key regulator of seed dormancy and stress responses, but its effects on seed germination depend on concentration, developmental stage, and environmental conditions. This study investigated whether exogenous ABA seed priming could alleviate low-temperature-induced inhibition of germination and improve early seedling establishment in direct-seeded rice.

Rice seeds were primed with different ABA concentrations and then exposed to low-temperature stress during germination and early seedling growth. Germination performance, reserve mobilization, respiratory metabolism, antioxidant responses, endogenous ABA and GA contents, selected SOD-related gene expression, and seedling growth traits were analyzed.

ABA seed priming showed concentration-dependent effects, with 40 μmol L^-1 ABA exhibiting the most favorable overall performance under low-temperature conditions. Compared with the low-temperature control, low-to-moderate ABA priming improved germination performance, enhanced α-amylase activity, increased soluble sugar accumulation, and increased respiratory rate. ABA priming also enhanced antioxidant enzyme activities and reduced H₂O₂ and malondialdehyde accumulation. Expression analysis of selected SOD-related genes showed gene-specific responses rather than uniform transcriptional activation. In addition, ABA seed priming was associated with lower endogenous ABA accumulation, higher GA content, and a reduced ABA/GA ratio under low-temperature stress. The beneficial effects observed during germination were partly maintained at the three-leaf stage, particularly in root growth, chlorophyll accumulation, and antioxidant capacity.

These results suggest that appropriate ABA seed priming can improve germination and early seedling establishment under low-temperature stress in direct-seeded rice, mainly through physiological adjustments involving reserve mobilization, oxidative damage mitigation, antioxidant responses, and endogenous hormonal status. Further studies involving GA metabolism genes, ABA signaling components, and additional mechanistic validation are needed.