FREEZE-FRACTURE OF SPERM OF PLUMBAGO-ZEYLANICA L IN POLLEN AND IN-VITRO

Sperm of Plumbago zeylanica are dimorphic with regard to numbers of mi tochondria and plastids. In most cases examined, the plastid-rich sper m fused with the egg while the sperm with fewer plastids fused with th e central cell, However, plastids cannot be directly responsible for f usion because fusion occurs between the plasma membranes of egg and sp erm. The question is whether sperm cell membranes are distinctive and possibly dimorphic. Sperm in whole pollen grains and isolated ed sperm were freeze-fractured, In pollen, freeze-fractured sperm appeared onl y in cross fractures. No extended membrane fracture faces of sperm wer e found. Among isolated sperm, two sizes of sperm with different lies were observed. Isolated sperm were assigned signed to two categories b ased on cell diameter and on size and density of organelles. Membrane particles on most sperm were arranged without distinctive pattern. Som e hexagonal arrays were observed. In sperm that had been maintained at 4 degrees C, particle-free areas, a probable consequence of lipid pha se separations, appeared on plasma membrane fracture faces. No unique fracture patterns and no patterns of dimorphism were detected on freez e-fractured plasma membranes of Plumbago sperm.