IN DRY PEAR (PYRUS-COMMUNIS L) POLLEN, MEMBRANES ASSUME A TIGHTLY PACKED MULTILAMELLATE ASPECT THAT DISAPPEARS RAPIDLY UPON HYDRATION

Ultrastructural details of dry (7% moisture content) and hydrated Pyrus communis L. pollen are revealed following freezesubstitution preparation for electron microscopy. Dry pollen is characterized by tightly packed, multilamellate membranous profiles found in association with plasma membrane, vesicles, ER, dictyosomes and some double-membrane bound organelles. Dry pollen also shows unit-membrane bound, densely osmiophilic bodies often with tightly packed multilamellations contained within and, at times, in their bounding membranes. These features are not evident in hydrated pollen. Results suggest that multilamellate membranes form as the plasma membrane, vesicles, ER, and double-membrane bound organelles undergo dehydration, and that upon hydration they rapidly resume normal unilamellate structure. © 1990 Springer-Verlag.