Structural equation modeling reveals proline as the dominant pathway governing rice seed germination under chilling...

Low-temperature stress limits the germination of direct-seeded rice (Oryza sativa L.), yet the physiological mechanisms underlying antioxidant defense and reserve mobilization remain unclear. Prohexadione-calcium (PC) modulates gibberellin biosynthesis and oxidative metabolism, while selenium (Se) functions as an antioxidant cofactor; however, their combined effects on cold-stressed germination in rice have not been systematically investigated in terms of integrated physiological regulation involving antioxidant and metabolic pathways.

Two rice varieties with contrasting cold sensitivity (Hajingdao 10, sensitive; Longjing 31, tolerant) were subjected to seed soaking treatments: water (control), selenium (Se, 0.3 mg L^-¹), prohexadione-calcium (PC, 0.1 mg L^-¹), PC+Se (0.1 + 0.3 mg L^-¹), and Se priming. Germination rate, emergence, yield, and physiological indices (antioxidant enzymes, proline, MDA, amylase, soluble protein) were measured under controlled and field conditions. Selenium priming (SP) showed a comparatively weaker improvement in germination and physiological traits than Se soaking and PC+Se treatment. Structural equation modeling (SEM) identified key physiological drivers of germination.

The combined PC+Se treatment significantly enhanced germination rate and seedling emergence compared with controls. SEM revealed that proline accumulation exerted a strong positive direct effect on germination rate, whereas α-amylase activity showed a significant negative effect. In contrast, SOD and POD did not show significant direct effects on germination rate, but contributed indirectly through modulation of oxidative stress and lipid peroxidation (MDA). No significant changes in gibberellin or abscisic acid were observed.

Low-temperature germination in rice is primarily driven by osmotic regulation, with proline accumulation acting as the key positive determinant, while carbohydrate mobilization (α-amylase activity) serves as a stress-sensitive limiting factor. Antioxidant enzyme responses contribute mainly as upstream physiological buffers rather than direct determinants of germination performance. PC+Se seed soaking is an effective strategy for improving early seedling establishment under chilling conditions.