INCREASES IN NUCLEAR-DNA CONTENT WITHOUT MITOSIS IN BENZYLADENINE-TREATED PRIMARY LEAVES OF INTACT AND DECAPITATED BEAN-PLANTS

Primary leaves of intact bean plants (Phaseolus vulgaris L. cv. Yamashiro-kurosando-saito) were treated with benzyladenine (BA) beginning on the seventh day after sowing when cell proliferation in the leaves had finished. Nuclear DNA contents were measured by cytofluorometry combined with 4',6-diamidino-2 phenylindole (DAPI) staining. In the untreated controls, most mesophyll and abaxial epidermal cells contained a nucleus whose DNA content was 2C; whereas most adaxial epidermal cells contained a 4C nucleus. Benzyladenine treatment induced 4C nuclei in mesophyll and abaxial epidermal cells; but BA induced 8C nuclei in adaxial epidermal cells. To compare the effects of endogenous cytokinin accumulation, bean plants were decapitated above the primary leaves on day 7 and continually disbudded thereafter. Changes in the nuclear DNA content in primary leaves attached to the decapitated plants was similar to that for BA-treated primary leaves. No multinucleate cells were formed and no mitotic figures were present in the BA-treated leaves or in the primary leaves of decapitated plants. Our results indicate that both BA treatment and decapitation induced one round of nuclear DNA synthesis without mitosis in a large number of mesophyll and epidermal cells.