Occurrence of mono- or disaccharides and polysaccharide reserves in mature pollen grains

Pollen from 13 species of gymnosperms and angiosperms was studied for soluble and insoluble carbohydrates at dispersal. Starch reserves stored during pollen development give rise to carbohydrates at maturity. Combinations of different types of carbohydrates in mature pollen may depend on the extent of starch hydrolysis. An inverse relationship was found between the extent of starch hydrolysis and sucrose content. If the starch was scarcely de-polymerized, the cytoplasm had very low levels of soluble sugars and none of the periodic acid-Schiff (PAS)-positive material as found in pollen not subject to high dehydration (Cucurbita pepo L., Zea mays L.). After total or partial starch hydrolysis, insoluble PAS-positive oligo/polysaccharides were found in the cytoplasm associated with much soluble sugar, and the pollen grains were dehydrated at dispersal as in Typha latifolia L., Chamaerops humilis L., Trachycarpus excelsa Wendl.. and other specimens. Intermediate levels of starch and soluble sugars, together with cytoplasmic PAS-positive material, characterized species with dehydrated pollen such as Pinus halepensis Miller. Carbohydrates may be related to pollen longevity, which largely depends on the abundance of sucrose, which is known to protect membrane integrity. The relationship between PAS-positive material and pollen viability is unclear at present.