EPTC Effects in the Lettuce (Lactuca sativa) Hypocotyl Bioassay for Gibberellins

Abstract

EPTC (S-ethyl dipropylthiocarbamate) reduces hypocotyl growth of lettuce [Lactuca sativa(L.) ‘Grand Rapids’] seedlings in response to gibberellic acid (GA3) in the lettuce hypocotyl bioassay. Doses of 0.01, 0.1, and 1.0 mM EPTC were effective over a range of gibberellin concentrations. Significant reductions in hypocotyl growth in response to all doses of EPTC and GA3at 7.68 μg/ml occurred between 12 and 24 h after initial treatment. In a 72-h experiment, pulse treatments of EPTC at 0.01, 0.1, and 1.0 mM plus GA3at 7.68 μg/ml for only 1 or 2 h at the beginning reduced the subsequent response of the bioassay when plants were transferred to GA3alone for the remaining 71 or 70 h, respectively. Final hypocotyl growth in GA3at 7.68 μg/ml was reduced by exposure to EPTC at 0.01, 0.1 and 1.0 mM plus GA3at any time during the entire 72 h test period. The interaction between EPTC and GA3was not due to herbicide-induced precipitation nor decomposition of GA3in the medium. This was demonstrated by separation of [14C]-GA3in four thin-layer chromatography solvent systems after incubation in the presence or absence of 1.0 mM EPTC for 48 h. Apparently EPTC can reduce the growth response of sensitive species to exogenous gibberellins in addition to its effects on endogenous gibberellin-like substances or gibberellin biosynthesis.