CYCLICAL TRANSFORMATIONS OF THE ACTIN CYTOSKELETON OF HYACINTH POLLEN SUBJECTED TO RECURRENT VAPOR-PHASE HYDRATION AND DEHYDRATION

Transformations of the actin cytoskeleton of the pollen of Hyacinthus orientalis during cycles of vapour-phase hydration and dehydration have been examined using a non-fixation, DMSO permeabilisation method for TRITC-phalloidin staining, coupled with microwave stabilisation. In freshly shed pollen actin appears: a) at the plasmalemma in the form of extended, thin fibrils co-oriented with the cellulosic microfibrils of the contiguous intine; b) as a sheath investing the generative cell; c) as spicules around the vegetative nucleus; and d) in scattered spicules in the cytoplasm. During hydration in 85-95% relative humidity (RH), actin from all of these sites is progressively translated into a system of extended fibrils in the vegetative cell, concurrently with the onset of movement in the cytoplasm. Dehydration at 5-7% RH reverses this process, actin accumulating in rodlets, spicules or larger fusiform bodies in close association with the generative cell and vegetative nucleus, and also in the cytoplasm. The fibril system initially present at the plasmalemma is not restored. After ten cycles of hydration and dehydration 3.6% of the grains remained germinable. The ecological significance of the findings is noted, and the possibility that the observed transformations result from variation in the Ca2+ concentration in the cytosol as the water content of the cytosol changes is considered.