PLANT PHYSIOLOGY , Vol 104, Issue 4 1193-1199, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Altered Phase Behavior in Membranes of Aging Dry Pollen May Cause Imbibitional Leakage
DGJL. van Bilsen, F. A. Hoekstra, L. M. Crowe and J. H. Crowe
Department of Plant Physiology, Agricultural University Wageningen, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands (D.G.J.L.v.B., F.A.H.)
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 (Tm) of isolated membranes and in a broadening of
the transition in situ. We conclude that the increase in Tm of hydrated
membranes may be more closely related to the leakage.