Membrane state and pollen viability

The relationship between germinability and fluorochromasia (FCR) has been studied in pollen of eight genera, Secale, Iris, Carex, Eleocharis, Cytisus, Digitalis, Plantago and Lonicera. The FCR tests two properties of the pollen, (a) the integrity of the plasmalemma of the vegetative cell and (b) the presence of an esterase capable of cleaving the fluorogenic ester, fluorescein diacetate. In general, the correlations between FCR and germinability were found to be very highly significant. This is interpreted as meaning that the primary determinant of pollen viability in short-term storage is the state of the vegetative cell membranes. It is suggested that in the partly dehydrated grain at the time of dispersal the membranes are largely dissociated and do not form an osmotic barrier, but that normal properties are recovered during controlled hydration which would normally take place on the stigma. According to this view, the decay of apparent viability is related to the progressive loss of the capacity of the vegetative cell membranes to regain a normal structure on rehydration. The genera investigated varied in their longevity in storage in low and high humidity conditions. After low-humidity storage, most showed some enhancement of germination with 1 h exposure to a humid atmosphere before transfer to the germination medium. During this 'conditioning' period the membranes recover their fluorescein retentivity in step with the increase in germinability