The effect of pectin and related compounds on encystment and germination of Phytophthora palmivora zoospores

Abstract

Citrus pectin and other uronic acids (polygalacturonate, alginate and galacturonate) accelerated encystment and germination in suspensions of Phytophthora palmivora zoospores. Other anions, polyanions and polysaccharides containing α(1→4) linkages were not effective in this respect. The uronic acids tested differed from one another both in the concentrations required for maximal rates of encystment and in the extent to which they stimulated germination as well as encystment. Pectin-accelerated encystment did not require free Ca2+ in the suspending medium, but when the Ca2+ concentration exceeded 100 μM, uronate-stimulated encystment and germination was suppressed. This blocking of uronate-accelerated encystment was almost specific for Ca2+, although Sr2+ and Ba2+ showed some effect. It is proposed that the action of uronates in accelerating encystment of P. palmivora zoospores is analogous to agonists which induce stimulus-mediated secretion in many animal cell types.