Localization of mistletoe lectins I-III in Viscum album L. by immunofluorescent labeling

Abstract

Because of immunomodulatory effects mistletoe extracts play an important role as phytotherapeutic adjuvants in cancer therapy. Mistletoe lectins I-III contribute to the in vivo activity of mistletoe preparations [1]. They consist of two chains: the A chain is a homologous protein for all mistletoe lectins and responsible for the inhibition of translation. The B chain is necessary for binding to specific carbohydrate epitopes; the protein sequence of this chain varies from lectin to lectin. The localization of bioactive lectins in Viscum album L. is of significance to understand the physiological role of lectins in the plant and to optimize the production of pharmaceutical preparations. We investigated the cellular distribution of lectins in different parts of the plant by immunofluorescent labeling. Leaves and internodes of shoots of Viscum album L. were treated with a monoclonal antibody against the A-chain of mistletoe lectins I-III. A secondary fluorescent-labeled antibody was added and the sections were analyzed by confocal laser scanning microscopy. The mistletoe lectins I-III were located mainly in cells of the parenchyma of the cortex, in sclerenchyma tissue next to the vascular bundles and in the companion cells of the phloem. Especially in parenchyma cells of the third and fourth internode a high content of lectins could be detected, whereas parenchyma cells of the leaves showed weak labeling only.