ESTIMATES OF NUCLEAR-DNA CONTENT IN BRYOPHYTE SPERM CELLS - PHYLOGENETIC CONSIDERATIONS

Nuclear DNA contents of developing sperm were estimated for 17 species of bryophytes by cytophotometry in squash preparations of antheridia after Feulgen staining. Genome sizes are in the lower end of the range for land plants. Two hornwort C-values have the lowest recorded for b ryophytes at 0.17 and 0.26 pg DNA per nucleus. In liverworts, C-values range from 0.49 pg in Blasia pusilla to 4.05 pg in Pellia epiphylla, while moss genome sizes are less variable, ranging from 0.38 pg in Tak akia ceratophylla to 0.92 pg in Atrichum oerstedianum. DNA content is not correlated with chromosome number in these bryophytes, but spew ce ll size and cellular complexity are directly related to C-value. Struc tural variations in the locomotory apparatus are viewed as evolutionar y modifications associated with changes in genomic complexity, with a generalized increase in complexity of the motile assemblage accompanyi ng increases in DNA content. Nuclear DNA values are not as variable in bryophytes as they are in pteridophytes and seed plants. We suggest t hat in plants producing biflagellated gametes, lower DNA contents affo rd a selective advantage. Comparisons with plants that produce multifl agellated or pollen-dispersed sperm indicate operation of a nucleotypi c effect in archegoniates with biflagellated sperm. This effect may be on sperm cell functioning, which in turn influences reproductive succ ess.