HETEROGENEOUS LIGNIFICATION IN ONE-YEAR-OLD SHOOTS OF TREES .1. CHARACTERIZATION OF CELL-WALL COMPONENTS IN THE VARIOUS TISSUES OF A ONE-YEAR-OLD POPLAR SHOOT

Chemical and histochemical analyses were made to examine the structure of lignin and carbohydrate of the pith in one-year-old shoots of a po plar (Poplus nigra L. X P. Maximowiczii A. Henry). Other tissue fracti ons, primary xylem, secondary xylem and bark also were investigated to be compared with the pith. It took the pith a much longer period to l ignify completely compared with the secondary xylem. The syringyl/guai acyl (S/G) ratio in the degradation products from the pith by alkaline nitrobenzene oxidation or thioacidolysis was the largest of all tissu e fractions. The ratio of primary xylem (PX) was the smallest: namely, its lignin was guaiacyl rich. The lignin content of the secondary xyl em was the largest, and the S/G ratio in this tissue was more than tha t in the primary xylem. The yield of p-hydroxybenzoic acid esterified to the pith was very small. This acid was located dominantly in the se condary xylem. The neutral sugar composition of the pith was similar t o that of the secondary xylem. The content of pectic substances was sm all in the pith and large in the primary xylem and bark tissues.