Histological observation of red pigment formed on shoot stem of Lithospermum erythrorhizon

Abstract

Shikonin production on the stem of shoot cultures of Lithospermum erythrorhizon was controlled by use of various culture media and light irradiation. Microscopic analysis of the shoot cultures revealed that the red pigment formation was only observed on the stem surface and the stem hairs of shoots cultured in the dark. Cross section of the shoot stem which formed red pigment in the dark was morphologically similar to that of shoots cultured under illumination. Red pigment accumulation was strictly localized in the outer surface of epidermal cells. The localization of these pigments was similarly observed in root tissues generated from the cultured shoots as well as field-grown roots. Northern blot analysis indicated that LEDI-2 gene, which is one of the candidates for the regulatory element of shikonin biosynthesis and specifically expressed in the root system of the intact plants, was also expressed in the stem of shoot cultures when producing shikonin.