An Evaluation of 2,5-Norbornadiene as a Reversible Inhibitor of Ethylene Action in Deepwater Rice

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Abstract
Parital submergence of deepwater rice (Oryza sativa L. cv Habiganj Aman II) elicits three responses: enhancement of internodal elongation, inhibition of leaf growth, and promotion of adventitius root formation. All three responses can be induced in isolated stem sections by treatment with ethylene. Dose-response curves indicate that the responses are linearly related to the logarithm of the ethylene concentration over two orders of magnitude. Application of the cyclic olefin 2,5-norbornadiene (NBD) to ethylene-treated sections results in a parallel shift in dose-response curves to higher ethylene concentrations, indicating that NBD behaves as a competitive inhibitor of ethylene action. Internodal elongation of stem sections is promoted by gibberellic acid (GA3) in the absence of exogenous ethylene. Endogenous ethylene levels do not increase in GA3-treated sections, and application of NBD does not prevent GA3-promoted elongation. To the contrary, NBD treatment results in increased growth at intermediate GA3 concentrations. These results support the idea that ethylene acts through endogenous GA in promoting growth in deepwater rice. NBD applied to GA3-treated stem sections results in increased ethylene production. This enhancement of ethylene formation is reversed by application of either ethylene or propylene, indicating that ethylene biosynthesis in rice internodes is under negative feedback control.