Inhibition of cell division and cell elongation in higher plants by inhibitors of DNA synthesis

Abstract

Lettuce seedlings were incubated in the presence and absence of gibberellin (GA 3) in solutions containing different inhibitors of DNA synthesis. GA 3 promoted the elongation of the lettuce hypocotyl in the dark, and of both hypocotyl and cotyledons in the light; 50% growth inhibition was obtained by 3 × 10 −7 M 5-fluorodeoxyuridine (FUDR). Inhibition produced by FUDR at 10 −7 to 10 −5 M was completely reversed by 10 −4 M thymidine, but not by uridine. The inhibition produced by amethopterin was only partly reversed by thymidine; 50% inhibition was obtained at 10 −7 M of amethopterin, 10 −5 M of mitomycin C, and 2 × 10 −3 M of phenethyl alcohol. In the inhibited tissues both cell division and cell elongation were suppressed. In epicotyls of decapitated lentil seedlings, which grow mainly by cell elongation, cell elongation was promoted by GA 3 and was inhibited by FUDR at 10 −7 to 10 −5 M. This inhibition was again reversed by thymidine, but not by uridine. The possible relationship between DNA synthesis and cell elongation in GA 3-promoted tissues is discussed.