Ascorbic acid in plants: Biosynthetic regulation and biotechnology strategies for enhancing human health.

Ascorbic acid (AsA) is a crucial water-soluble antioxidant in plant cells, playing a central role not only in plant growth, development, and stress responses but also serving as an essential nutrient for human health. Since the human body cannot synthesize AsA independently, its intake primarily relies on fresh fruits and vegetables. This paper reviews, from a plant physiological perspective, how AsA accumulation is finely regulated by multiple processes including biosynthesis, transport, degradation, and regeneration cycles. It discusses how environmental signals trigger a series of changes in endogenous signaling molecules within plants, thereby activating multi-level regulatory networks that influence AsA synthesis and metabolism. It highlights that enhancing crop AsA content through genetic engineering and agronomic measures has become a research hotspot. In particular, biofortification, the process of augmenting the nutritional quality of food crops through genetic engineering, conventional breeding, or agronomic practices, represents a sustainable and promising strategy to increase AsA levels in staple crops and combat micronutrient malnutrition. Finally, it explores future research directions aimed at overcoming the "ceiling effect" caused by feedback inhibition and redox homeostasis, ultimately achieving the goal of promoting human health by enhancing plant health.