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 proliferationin the leaves had finished. Nuclear DNA contents were measuredby cytofluorometry combined with 4',6-diamidino-2-phenylindole(DAPI) staining. In the untreated controls, most mesophyll andabaxial epidermal cells contained a nucleus whose DNA contentwas 2C; whereas most adaxial epidermal cells contained a 4Cnucleus. Benzyladenine treatment induced 4C nuclec in mesophylland abaxial epidermal cells; but BA induced 8C nuclei in adaxialepidermal cells. To compare the effects of endogenous cytokininaccumulation, bean plants were decapitated above the primaryleaves on day 7 and continually disbudded thereafter. Changesin the nuclear DNA content in primary leaves attached to thedecapitated plants was similar to that for BA-treated primaryleaves. No multinucleate cells were formed and no mitotic figureswere present in the BA-treated leaves or in the primary leavesof decapitated plants. Our results indicate that both BA treatmentand decapitation induced one round of nuclear DNA synthesiswithout mitosis in a large number of mesophyll and epidermalcells.