Melanin found in wheat spike husks

Abstract

Melanin is the dark polymer pigment found in all kingdoms of life. Plant melanin, formed through the oxidation and polymerization of phenolic compounds, does not contain nitrogen, however it possesses similar properties with melanin of animal, fungal or bacterial origin. Melanin in plants is usually found in seed coats or fruit pericarp and is ascribed mechanical barrier or some other protective functions. Wild and formerly locally cultivated wheat species, like Persian wheat (Triticum carthlicum Nevski) frequently exhibit black color of spike husks and awns. The pigment causing it and the biological purpose of this coloration was not clarified before. In this paper using standard chemical extraction procedures for anthocyanins and melanin, ultraviolet-visible-near-infrared spectroscopy and hyperspectral imaging, we prove that the black color of Persian wheat spikes is caused by melanin but not anthocyanins. Also, we show that the dark pigment in husks and awns is located in epiderma and subepidermal sclerenchyma cells, that implies melanin potentially to have mechanical-enhancing and protection function. Other possible functions of melanin in cereals are discussed.