Synthesis of noncellulosic cell-wall β-glucan by cell-free extracts from zoospores and cysts of Phytophthora palmivora

Abstract

Zoospores of Phytophthora palmivora, induced to encyst by vigorous agitation, synthesize alkali-insoluble β-glucans at a linear rate for ca. 10 min. Cell-free extracts of zoospores and cysts of P. palmivora contained particulate enzymes capable of synthesizing alkali-insoluble, noncellulosic β-1,3-, β-1,6-glucans from uridine diphosphate glucose. Similar levels of activity were detected in zoospores and cysts. Enzymatic activity was stimulated by Mg 2+; Ca 3+ and Mn 2+ were less effective. Cellobiose and other β-linked glucose disaccharides were strong activators. Evidently, the swimming zoospore is equipped with the enzymatic ability to make insoluble, noncellulosic β-glucan—a major component of the cyst wall; hence, a mechanism must exist which prevents the operation of glucan synthetase(s) until the time of encystment. The cell-free extracts also had the ability to synthesize soluble β-1,3-glucan. Most of this material was characterized as neutral mycolaminaran and mycolaminaran phosphate.