Recently developed techniques for the isolation of sex cells of flowering plants represent an important first step toward eventual detailed cytological and biochemical analyses and experimental manipulations of higher plant gametes that was not previously possible. In the present investigation we have analysed a population of isolated viable male gametes from the standpoint of qualitative and quantitative ultrastructure in order to elucidate the process of double fertilization in angiosperms. The vast majority of the Zea mays sperm cells were found to be structurally intact spherical cells. Morphometric analysis of 400 isolated sperm cells indicates that the average cell is 7.66 μm in diameter, has volume and surface areas of 235.3μm3 and 184.3μm2, respectively, and contains a variously shaped, often curved nucleus, which occupies 38.5% of the cell volume. Other cell constituents and their relative volumes (expressed as percentages of the protoplasm) included in the analysis are: vacuoles, 9.3%; endoplasmic lamellae, 5.9%; mitochondria, 3.5%; osmiophilic bodies, 1.2%; Golgi complex, 0.6%; and hyaloplasm (back-ground cytoplasm), 41.1%. No plastids or microtubules were observed in the hybrid line used.
Two types of nuclei were found, i.e. heterochromatic and non-heterochromatic. Although statistical analysis of cell components shows some significant differences between cells of the two nuclear types, we do not believe that they represent the two sperms of a pair within pollen grains, since they do not occur in a 1:1 ratio. It is more likely that the variability within the sperm population is the result of slightly different developmental states at the time of anther dehiscence.
Sperm cells of Zea mays
have a complex complement of mRNAs