Multiple functional roles of anthocyanins in plant-environment interactions

• Anthocyanins protect plant tissues/organs against many abiotic stressors.
• Different mechanisms of protection (sunscreen, antioxidant, metal-chelating) have been proposed for anthocyanins.
• We also explore the possibility that anthocyanins might act to delay senescence in plants facing mineral deficiency.

Almost a century after Muriel Wheldale’s landmark publication, “The Anthocyanin Pigments of Plants” (Wheldale, 1916), much about anthocyanin function in plants remains to be elucidated, even though the environmental drivers and biosynthetic pathways leading to anthocyanin production are well established. That anthocyanins may protect leaves in plants facing biotic or abiotic stressors, an idea dating back to Pringsheim (1879), is arguably the most widely accepted function for foliar anthocyanins, although the mechanism(s) by which they could mitigate effects of stress remains heatedly debated. In addition to the most frequently discussed putative roles of anthocyanins as antioxidants and sunscreens, other less-explored possibilities might equally serve to ameliorate plant function under, for example, under conditions of mineral imbalance. In particular: (i) anthocyanins may serve as metal-chelating agents under conditions of excess edaphic metal ions and (ii) anthocyanin accumulation might delay foliar senescence, which is otherwise usually accelerated in plants growing under macronutrient deficiency. The latter mechanism might be particularly advantageous to prolong plant survival and increase the possibility of reproductive success.