Can Anthocyanins be Part of the Metal Homeostasis Network in Plant?

Anthocyanins are a class of flavonoids with a high level of diversification and likely the most studied pathway of secondary metabolism in Plantae. Anthocyanins have raised a growing interest due to the huge variability of their chemical structures and the more new anthocyanins are isolated from plants, the more questions on their evolutionary and ecological meaning they raise. Antioxidant, photoprotection against high light and UV, defence against herbivores and pathogens, attraction of pollinator are only some proposed biological functions for those versatile compounds. Anthocyanins have also been found complexed with metal ions either in flower pigments (commelin and protocyanin) or in leaves and stems. Due to the potentiality of anthocyanins to chelate to metals, their involvement in the attenuation of metal toxicity has been recently proposed. Conversely, the ability of plants to remobilize metal ions from stored metal-anthocyanin complexes when plants experience a period of transient metal shortage has never been investigated before. The aim of this paper is to support the hypothesis that the anthocyanin-metal interactions might represent a further ecological role for these pigments and also that anthocyanins can be part of the complex network of metal homeostasis in plant.