Unraveling the role of autophagy and antioxidants in anther and pistil responses to heat stress in rapeseed (Brassica napus L.)

Enhanced antioxidant enzymes activity, particularly superoxide dismutase and catalase, along with autophagy process in reproductive organs, can improve the resilience of rapeseed to heat stress, thereby securing crop yield in the face of global warming. Climate change and global warming have increasingly influenced yield and quality of rapeseed (Brassica napus) almost all across the world. The response of reproductive organs to high-temperature stress was studied in two rapeseed varieties, SAFI5 and DH13 with contrasting levels of heat stress tolerance. Pollen germination, viability, and seed set showed a significant reduction in the heat-sensitive variety (DH13). Superoxide quantification revealed higher accumulation in heat-sensitive variety, leading to decreased seed formation and floret fertility most probably due to declined pollen viability and stigma receptivity. Further microscopic analysis of the anther and pistil demonstrated a significant overlay between the damaged areas and the location of O₂^- accumulation. The sensitive variety showed higher O₂^- accumulation and a wider damage area than the tolerant one, suggesting that superoxide could incapacitate anther and pistil due to structural injury. Moreover, the activity levels and expression of superoxide dismutase and catalase antioxidant enzymes were significantly higher in the anther and pistil of the tolerant variety. Histochemical analysis also indicated markedly higher autophagosome formation in tolerant variety's anther and pistil. Consistently, the expression levels of autophagy and ubiquitin-proteasome system (UPS)-related genes including BnATG8d, BnEXO70B, BnATl1 4A, and BnNBR1, as well as ubiquitin-activating enzyme E1, were higher in both reproductive organs of the tolerant variety. Interestingly, the areas of autophagosome formation overlapped with the areas in which higher superoxide accumulation and structural changes happened, suggesting a specific role of autophagy in oxidative stress response.