Anthocyanins act as a sugar-buffer and an alternative electron sink in response to starch depletion during leaf senescence: a case study on a typical anthocyanic tree species, Acer japonicum.

This article investigates the role of anthocyanins in leaf senescence of fullmoon maple (Acer japonicum), focusing on their function as a sugar-buffer and alternative electron sink to prevent early senescence and photoinhibition under varying light conditions within the tree canopy. Through seasonal monitoring of photosynthetic traits, pigment composition, sugar and starch contents, nitrogen levels, and gene expression, the study found that anthocyanin accumulation in sun-exposed leaves correlates with starch depletion and may regulate sugar levels while maintaining electron transport to protect against photoinhibition. Gene expression analyses revealed synchronized regulation of chlorophyll and carbohydrate metabolism genes independent of light, whereas anthocyanin biosynthesis genes responded to light conditions, supporting a transcriptional control linked to photoprotection. The findings support the "holocanopy hypothesis," suggesting that anthocyanins help outer-canopy leaves resist photoinhibition and delay senescence, thereby facilitating efficient nitrogen resorption for the whole canopy.