Deciphering Biochemical and Molecular Insights into Proline Induced Mitigation of Postharvest Senescence in Hemerocallis lilioasphodelus L. Scapes

Senescence, a terminal phase in flower development, involves intricate biochemical and molecular changes that contribute to cellular aging, tissue degradation and eventual death. This study investigates the potential of exogenous proline to modulate these processes, delaying postharvest senescence in scapes of Hemerocallis lilioasphodelus, an ethylene-insensitive flower system. Proline application significantly extended scape longevity by orchestrating key biochemical and molecular responses. Proline treated scapes exhibited elevated soluble protein, sugar and phenolic content, maintained membrane integrity and reduced bacterial proliferation in vase solutions, resulting in improved water uptake. Antioxidant enzyme activities, including superoxide dismutase, catalase and ascorbate peroxidase were enhanced while lipoxygenase activity decreased, indicating mitigated oxidative stress compared to control group. At the molecular level, proline treatment at 45 mM downregulated Senescence-Associated Gene 12 (SAG12) and Lipoxygenase 1 (LOX1) while upregulating Defender Against Death 1 (DAD1), suggesting a positive regulatory effect on cellular longevity. In contrast, untreated scapes (control group) showed increased SAG12 and LOX1 expression, along with decreased DAD1 expression, correlating with accelerated senescence. Our study concludes that proline delays flower scape senescence not only by orchestrating biochemical activities but also by modulating senescence-associated gene expression.