Determination of the distribution and reaction of polysaccharides in wood cell walls by the isotope tracer technique VIII: Selective radiolabeling of xylan in mature cell walls of magnolia (Magnolia kobus DC.) and visualization of its distribution by microautoradiography

Abstract

To radiolabel xylan in mature cell walls selectively, magnolia (Magnolia kobus DC.) was administered withmyo-inositol-[2-3H] and allowed to metabolize for 1 month. The radiolabeled xylem tissue was then submitted to sulfuric acid hydrolysis and nitrobenzene oxidation. A large amount of radioactivity was found mainly in xylose, although slight activities were detected in glucose and in vanillin and syringaldehyde. The labeled tissue was submitted to a preparation of holocellulose followed by treatment with 24% potassium hydroxide (KOH). Radioactivity was distributed mainly in the KOH-soluble part of the holocellulose. These results indicate that most radioactivity was incorporated into xylan in the cell walls. The distribution of the incorporated radioactivity in the xylem tissue was visualized by microautoradiography. Radioactivities were distributed in the xylem more than 400 μm from the cambium; and an inner layer of a secondary wall had formed at the labeled xylem. Consequently, selective radio-labeling of xylan was visualized in mature cell walls.