NUCLEAR-DNA CONTENT IN DIFFERENTIATED TISSUES OF SUNFLOWER (HELIANTHUS-ANNUUS L)

Scanning cytophotometry following Feulgen-staining was used to determine nuclear DNA content in many differentiated tissues of nine cultivars, hybrids or selfed lines of Helianthus annuus. Apart from such ephemeral tissues as endosperm and anther tapetum, it was found that tissue differentiation in sunflower occurs in the diploid condition, cells being arrested in the DNA presynthetic phase (G 1). In certain cases, however, the nuclear DNA content of differentiated G 1 cells does not exactly match the 2C DNA content found in meristematic cells, but may be either higher or lower. In endosperm and anther tapetum cells, nuclear DNA content may be as high as 24 C and 32 C, respectively. Cytological and autoradiographic analyses after 3H-thymidine incorporation reveal that polyploidy in the tapetal cells is due to chromosome endoreduplication. No detectable difference between male-fertile and male-sterile plants exists as far as occurrence and level of cell polyploidy are concerned. The results are discussed in the context of previous investigations on the nuclear condition of differentiated Helianthus annuus tissue