Effects of acidity on the insoluble polysaccharide content of germinating pollen of Pinus pinea L. and Pinus pinaster Aiton

The PAS reaction was used to slain total insoluble polysaccharides in pollen of two species of Pinus collected in two different years and germinated in vitro at different pH values. PAS-detectable polysaccharides are localized in the inline, cytoplasm and amyloplasts; PAS-undetectable (callose) in the middle of the intine, but only in the distal part of the grain. The total PAS stained polysaccharide content was quantified with a microdensitometer. Values are correlated with germination percentages and pollen tube length. The total polysaccharide content, as well as pollen tube length, varies in each species according to the year, probably due to environmental conditions. Also the various pHs deeply influence pollen germination and tube length, the lowest pH being the most unfavourable condition. At this pH (3.5) the total polysaccharide content is higher than in the control (pH 5.5): this is probably due to a lack of callose synthesis for tube wall or to a depolymerization of this polysaccharide, and a subsequent storage in a PAS-detectable form.