CYTOLOGICAL CHARACTERIZATION OF ISOLATED SPERM CELLS OF PERENNIAL RYEGRASS (LOLIUM-PERENNE L)

The cytoplasmic content and the distribution of intramembrane particle s (IMPs) of the plasma membrane of isolated sperm cells of perennial r yegrass (Lolium perenne L.) have been characterized using flow cytomet ry, transmission electron microscopy, confocal scanning laser microsco py and freeze-fracture studies. The isolated haploid sperm cells conta in a variety of cell organelles with the exception of microtubules. Pr oplastids and plastids with starch were observed, although only rarely . Vacuoles containing remnants of organelles and stacked lamellae of e ndoplasmic reticulum with cytoplasmic inclusions were observed frequen tly, indicating that autophagy takes place. The number of mitochondria varies from 11 to 26 with an average of 17. Generally, the nucleus ha s a lobed shape and displays various interphasic stages of chromatin c ondensation. The analysis of the number of mitochondria and the nuclea r state did not show evidence of sperm cell dimorphism. The cytologica l variability observed, could be explained by differences in developme ntal stages already present in vivo at the moment of isolation. No cor relation between the number of mitochondria and the nuclear cross-sect ioned area and/or the condensation state of the chromatin could be fou nd. The density of intramembrane particles of the plasma membrane on t he exoplasmic fracture face is more than twice that on the protoplasmi c fracture face. That is the opposite of what was found for sporophyti c cells of perennial ryegrass. These results are discussed in relation to the potential use of these cells for biotechnology and development al studies.