Plant and Cell Physiology, 2001, Vol. 42, No. 10 1056-1061
© 2001 Oxford University Press
IAA and N6-Benzyladenine Inhibit Ethylene-Regulated Expression of ACC Oxidase and ACC Synthase Genes in Mungbean Hypocotyls
Department of Biology, Yonsei University, Seoul 120-749, The Republic of Korea
Regulation of expression of 1-aminocyclopropane-1-carboxylate (ACC) oxidase (VR-ACO1) and ACC synthase (VR-ACS1) genes by ethylene, indole-3-acetic acid (IAA), and N6-benzyladenine (BA), was investigated in mungbean hypocotyl tissues. Exogenous ethylene markedly increased transcript level of VR-ACO1 and reduced that of VR-ACS1, whereas aminooxyacetic acid (AOA), an inhibitor of ethylene biosynthesis, decreased the level of VR-ACO1 mRNA and increased that of VR-ACS1, indicating that expression of VR-ACO1 and VR-ACS1 genes are under positive and negative feedback control by ethylene, respectively. However, IAA treatment reduced the level of VR-ACO1 transcripts and increased that of VR-ACS1, although the hormone greatly induced ethylene production. We have demonstrated that, in a system that separates the effect of IAA proper from the effect of IAA-induced ethylene, the amount of IAA-induced ethylene was enough to cause accumulation of VR-ACO1 mRNA and decrease of VR-ACS1 mRNA. We have also shown that the responsiveness of VR-ACO1 and VR-ACS1 to exogenous ethylene was greatly reduced in the presence of IAA. In addition, BA abolished ethylene responsiveness with respect to expression of VR-ACO1 and VR-ACS1. Based on these results, we suggest that IAA and BA inhibit ethylene action, resulting in suppression of VR-ACO1 expression and induction of VR-ACS1 expression.
1 Present address: MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824-1312, U.S.A.
2 Corresponding author: E-mail, kimjeon4@msu.edu; Fax, +1-517-353-9168.