An anomalous wall thickening and its possible role in the uptake of stem-fed tritiated glucose by Pinus pinea

Abstract

An unusual form of secondary thickening has been found on certain cells adjacent to the innermost xylem tracheids of the stem. If a stem tip is fed with tritiated glucose at the cut base, cells with the thickening accumulate the label in the starch of their plastids. This is demonstrated by autoradiography. Label is also found in the starch of the xylem ray cells and the most recently formed xylem tracheids and phloem elements. Functions for the unusual thickening and possible routes of glucose uptake are discussed.