Changes in the Coagulating Ability of Pectin during the Growth of Soybean Hypocotyls

The hypocotyl of a 3-day-old dark-grown soybean seedling was cut into the hook segment and seven 5-mm segments of the straight portion. Wall fractions, prepared from the segments, were boiled in 0.2 M NaCl solution to extract pectin. The lower the tissue was located, the less pectin was found in the neutral residues and the stronger was the tendency to coagulate in the presence of pectin methylesterase and Ca2+. Chromatography on a column of Sepharose 2B gave two subfractions each of polyuronide; the one with the higher mol wt was termed A pectin and the other, B pectin. The lower the tissue, the lower was the ratio of A pectin/B pectin. B pectin coagulated in the presence of pectin methylesterase and Ca2+ whereas A pectin did not. The coagulation of B pectin was strongly inhibited by A pectin obtained from the upper region (the hook and upper 1 cm of the straight portion) of the hypocotyl. The possible role of the pectin change in controlling cell growth is discussed.