Aging of cattail (Typha latifolia 1.) pollen was studied at 24°C under conditions of 40 and 75% relative humidity (RH). The decline of viability coincides with increased leakage at imbibition; both processes develop much faster at the higher humidity condition. During aging phospholipids are deesterified and free fatty acids (FFAs) and lysophospholipids (LPLs) accumulate, again, much more rapidly at 75% RH than at 40% RH. The fatty acid composition of the remaining phospholipids hardly changes during aging, which suggests limited involvement of lipid peroxidation in the degradation process. Tests with phospholipase A2 revealed that the saturated fatty acids occur at the sn-1 position of the glycerol backbone of the phospholipids. The fatty acid composition of the LPLs is similar to that of the phospholipids from which they were formed, indicating that the deesterification occurs at random. This favors involvement of free radicals instead of phospholipases i n the deesterification process. Liposome studies were carried out to characterize components i n the lipid fraction that might account for the leakage associated with aging. Entrapped carboxyfluorescein leaked much more from liposomes when they were partly made up from total lipids from aged pollen than from nonaged pollen.The components causing the leakage were found i n both the polar and the neutral lipid fractions. Further purification and subsequent interchanging of the FFAs and LPLs between extracts from aged and nonaged pollen revealed that in neutral lipid extracts the FFAs are entirely responsible for the leakage, whereas i n the phospholipid fraction the LPLs are largely responsible for the leakage. The leakage from the liposomes i s not caused by fusion. We suggest that the observed loss of viability and increased leakage during aging are due to the nonenzymic accumulation of FFAs and LPLs in the pollen membranes.

Aging of dry pollen has been shown to coincide with increases of free fatty acids and lysophospholipids. These compounds reduce the integrity of hydrated liposomes made from isolated pollen phospholipids but do not lead to their total destruction. However, a massive, instantaneous leakage occurs upon imbibition of dry cattail pollen (Typha latifolia) that has aged to the point of complete loss of viability. To resolve the apparent discrepancy in stability between hydrated and dry membranes, the lyotropic phase behavior of two liposome systems containing lysophospholipid (12 mol%) was studied with differential scanning calorimetry and Fourier transform infrared spectroscopy. In both systems dehydration caused phase separation of the lipids. Fourier transform infrared data concerning phase behavior of isolated membranes from aging pollen and of membranes in situ did not show phase separations, probably because the assay technique was not sufficiently sensitive to detect them. However, aging of the pollen resulted in a permanent increase in the gel-to-liquid crystalline phase transition temperature (1,) of isolated membranes and in a broadening of the transition in situ. We conclude that the increase in 1 , of hydrated membranes may be more closely related to the leakage.