Possible Role Of Nonenzymatic Antioxidants In Hydroprimed Sunflower Seeds Under Heat Stress

This work demonstrates how priming durations affect high- and low-vigor sunflower (Helianthus annuus L.) seeds and relate to the dynamics of enzymatic and nonenzymatic antioxidant systems against heat stress. Heat tolerance of high-vigor seeds were enhanced when primed 3-6 h, and low-vigor seeds were enhanced when primed 3-12 h. Priming at optimum duration led to increases in ascorbate peroxidase (APX) activity and higher levels of total phenolic content (TPC), vitamin C and total chlorophyll combined with decreased H2O2 content. After exposure to heat stress, the primed seeds maintained reactive oxygen species (ROS) levels and alleviated seeds damage. This may be due to protective mechanisms of priming that prevented severe loss in catalase (CAT) and APX activities, maintained superoxide dismutase (SOD) activity, and increased TPC, proline, vitamin C, and carotenoid accumulation. However, extending priming to 18 h with subsequent heat stress decreased germination percentage. Control seeds lost viability, as oxidative balance was not maintained due to heat stress. These results support the participation of nonenzymatic antioxidants in the improved tolerance to heat stress of primed seeds.