The growth of the grass pollen tube: 1. Characteristics of the polysaccharide particles (“P-particles”) associated with apical growth

Summary

Numerous polysaccharide-rich particles (“P-particles”) occur in the tip region of growing grass pollen tubes, where they apparently contribute to the extending wall. In other families the corresponding bodies have been shown to originate from dictyosome activity during pollen tube growth. However, in the grasses the main synthesis precedes anthesis; the P-particles represent up to 30% of the reserves of the vegetative cell of the dormant grain, numbering over one million in the pollen grain of rye. Their membranes are incomplete. The polysaccharide content, which is initially coarsely granular but becomes microfibrillar with hydration, is readily extracted with ammonium oxalate, and is probably pectic in nature. Simple methods for isolating the particles in relatively pure populations are described. Hydrolysis yields principally galactose, arabinose, glucose, and rhamnose. Apart from proteins derived from the original bounding membranes, a protein fraction is tenaciously bound to the polysaccharide. Isolated P-particles move anodically in an electrical field, and the possibility that their movement from the grain to the tube tip during growth depends on a potential gradient, already demonstrated for lily pollen tubes, is considered.