Novel Phosphoglucans from the Cytoplasm of Phytophthora palmivora and Their Selective Occurrence in Certain Life Cycle Stages

The cytoplasm of Phytophthora palmivora is rich in soluble β-(1 → 3)-glucans of which two different types can be recognized. The glucans extracted from the mycelium are all neutral molecules. In the asexual reproductive stages (sporangia, zoospores, and cysts) neutral glucan is also present but the main component is a family of novel phosphoglucans. By ion exchange chromatography, five different phosphoglucan fractions were detected with glucose to phosphate ratios ranging from 33:1 to 18:1. The phosphate was largely removed from the phosphoglucans by phosphomonoesterases. Phosphodiesterase had no effect. On enzymatic dephosphorylation, all phosphoglucans yielded a neutral glucan similar to, if not identical with, the neutral glucan concurrently found in the cytoplasm. The mobility of phosphoglucans in gel filtration was highly affected by the ionic strength of the cluant. The phosphoglucans have an average degree of polymerization of ∼30 and contain one or two phosphate groups linked by monoester linkage to the C-6 hydroxyl of a glucose residue(s). The absence of phosphoglucans in the mycelium, their subsequent appearance in the sporangia, and their partial utilization by the zoospores during encystment suggest that these polymers may play a major role in the biochemistry of cellular differentiation.