Anthocyanin pigmentation in the adventitious roots of Metrosideros excelsa (Myrtaceae)

Abstract

Anthocyanin pigmentation is a prominent feature in the adventitious roots Of Metrosideros excelsa. We describe the histological distributions and chemical nature of anthocyanins in these roots, and quantify their antioxidant activity. Anthocyanins were present in one or more cell layers of the root cap, epidermis, hypodermis, and cortex. A narrow band immediately behind the root apex was usually anthocyanin free. Photosensitivity of anthocyanin biosynthesis was evident both for adventitious roots and for plagiotropic roots exposed at the soil surface. The anthocyanins were cyanidin‐ and delphinidin‐based. Methanolic extracts of the roots did not show a direct relationship between anthocyanin concentration and antioxidant activity. The possible function of anthocyanins in these roots is unknown.