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 ge rminated in vitro at different pH values. PAS-detectable polysaccharid es are localized in the inline, cytoplasm and amyloplasts; PAS-undetec table (callose) in the middle of the intine, but only in the distal pa rt of the grain. The total PAS stained polysaccharide content was quan tified with a microdensitometer. Values are correlated with germinatio n percentages and pollen tube length. The total polysaccharide content , as well as pollen tube length, varies in each species according to t he year, probably due to environmental conditions. Also the various pH s deeply influence pollen germination and tube length, the lowest pH b eing the most unfavourable condition. At this pH (3.5) the total polys accharide content is higher than in the control (pH 5.5): this is prob ably due to a lack of callose synthesis for tube wall or to a depolyme rization of this polysaccharide, and a subsequent storage in a PAS-det ectable form.