In vivo hydration and pollen germination in Crocus vernus ssp. vernus as a function of humidity

The hydration and germination of Crocus vernus ssp. vernus pollen were examined when placing pollen on the stigma papillae under 10% to 100% relative humidity (RH). Following adhesion of the pollenkitt to the papilla, the pollen grain hydrates and swells up to emit a pollen tube, and its adjoined pollen grains may bypass contact with the papilla for hydrating and germinating. The hydration capacity increases in parallel to both the pollen dryness and the RH increase, but dry pollen does not reach full hydration. Without being placed on the stigma, dry pollen shows a moderate capacity to absorb water from the moist air, and slightly dehydrated pollen tends to lose water. Germination on the stigma shows the main increment in the interval of 20-40% RH, with a linear increase from 35.2% to 82.5%. Under 20% RH, the germination is low and inhomogeneous, while at over 40% RH it stabilizes, until it increases again at over 70% RH, with slightly different peaks for dry (86.3%) and undehydrated (94%) pollen at 90-100% RH. The results are discussed from cytophysiological viewpoints.