AN INTERMEDIATE-VOLTAGE ELECTRON-MICROSCOPIC STUDY OF FREEZE-SUBSTITUTED GENERATIVE CELL IN PEAR (PYRUS-COMMUNIS L) - FEATURES WITH RELEVANCE TO CELL-CELL COMMUNICATION BETWEEN THE 2 CELLS OF A GERMINATING POLLEN

The ultrastructure of the generative cell (GC) wall complex in germina ting pear (Pyrus communis L.) pollen was studied with the aim of ident ifying features that may shed light on the mechanism of uptake of subs tances by the GC from its host, the vegetative cell (VC). The techniqu es of rapid freeze-fixation and freeze-substitution, serial sectioning , and conventional and intermediate-voltage transmission electron micr oscopy were employed. The wall complex consisted of two plasma membran es (PMs), one derived from the GC and the other from the VC. A nonfibr illar wall material occurred in the space between the two PMs. Plasmod esmata could not be identified in this wall complex. However, in local ized areas the wall complex formed processes that protruded into the V C cytoplasm. In other areas, the wall complex showed certain cup-shape d invaginations. Certain double membrane bound multivesicular bodies o ccurred in the GC cytoplasm; their morphological characteristics indic ated that they may have been derived from the GC wall complex. The dat a indicate that in pear the GC surface is amplified by wall processes, presumably to perform a role analogous to transfer cells.