Abstract
Lectins are widely distributed in extracts of stems from woody plants. They are localized in the vacuole or protein bodies of phloem parenchyma existing in the inner bark. Lectins in the bark show an annual rhythm in that they decrease in spring and increase in the autumn. Therefore, it is suggested that lectins in bark have a function for the storage of nutrients. During the active period of secondary growth, from May to August, lectin decreased mainly in the outermost region of inner bark where the cork tissue differentiates and dilatation (see middle of the second paragraph in Chapter C) occurs. This result suggests that lectin is consumed in the process of cork tissue differantiation and/or dilatation. Recently, unique lectins in their binding specificities were found in barks. One binds to N-acetylneuraminic acid-containing oligosaccharides and the other binds to mannose, although most of the bark lectins bind to either N-acetylglucosamine or N-acetylgalactosamine. It has been hypothesized that lectins specific for N-acetylglucosamine and N-acetylneuraminic acid function as a defense system. However, the exact function of lectin in tree stems has not yet been established.
