Isolation and Chemical Composition of Oospore-Oogonium Walls of Phytophthora megasperma var. sojae

SUMMARY: The entire sexual apparatus (oospore-oogonium-antheridium, or ooa) of Phytophthora megasperma var. sojae was isolated in large quantities free of mycelium. The cells were fractured in a Teflon tissue homogenizer and the wall fraction was washed with a cytoplasmic dialysate to prevent agglutination and a tendency to adhere to glassware. The wall preparations were a mixture of oospore and oogonium walls (oow) and probably unrecognizable antheridial wall fragments. The walls constituted 47% of the dry weight of the ooa. Insoluble glucans comprised almost 80 % of the wall; the main component was non-cellulosic β-glucan(s) linked mainly through the 3-position. Less than 10% of the oow was cellulose. In addition to glucose, there were small amounts of mannose and glucosamine in the wall polymers. Proteins comprised about 12% of the oow; the most abundant amino acids were arginine and glycine. Hydroxyproline, a component of oomycetous hyphal walls, was also present. Readily extracted lipids varied from 2·8 to 5·9%, while bound lipids comprised 5·4 to 5·9% of the wall. Most of the readily extractable lipids of the ooa were found in the walls whereas bound lipids were mainly in the cytoplasmic fraction. Sterols (0·025%) were detected in the readily extracted lipid fraction. Phosphorus amounted to 0·55 % of the oow. There was substantial similarity in gross chemical composition between oow and hyphal walls of Phytophthora spp.