Incorporation of radioactivity into wheat xylem walls.

Studies on the fine structural changes accompanying xylem differentiation in wheat coleoptile have indicated that the microtubules are concerned with the inception of a regular wall thickening pattern, and later with wall deposition at the thickening site. The endoplasmic reticulum is situated characteristically in continuous profiles between the thickenings. Radioautographic studies at the electron microscope level using labelled glucoses have shown that the endoplasmic reticulum, golgi bodies and the cytoplasm near the microtubules were often labelled during deposition into nearby thickenings of radioactive materials derived from the tritiated glucoses. Incorporation into the wall occurred mainly at the top of the thickenings. The plastids of the xylem cells were also often labelled, but only during the earlier stages of differentiation; when massive wall deposition was evident, such an incorporation was never observed. The fine structural and radioautographic results are briefly discussed in terms of the possible functions of the organelles in the plant cell.