Temporal and spatial regulation of the expression of 1‐aminocyclopropane‐1‐carboxylate oxidase by ethylene in mung bean (Vigna radiata)

Abstract

Ethylene induced an increase in the level of 1‐aminocyclopropane‐1‐carboxylate oxidase (VR‐ACO1) transcript in mung bean hypocotyls. Time course study revealed that the level of the VR‐ACO1 mRNA in excised mung bean hypocotyls increased after 2‐h ethylene treatment and much higher mRNA levels were observed thereafter, while the basal level of transcript was slightly decreased in control tissues. The in vivo ACC oxidase activity increased from 31 nl g−1 h−1 at zero time to maximum activity of 62 nl g−1 h−1 at 10‐h ethylene treatment. Polyclonal antibody against VR‐ACO1 protein expressed in E. coli cells was generated. Immunoblot analysis using the resulting antiserum showed that the induction pattern of ACC oxidase polypeptide was in parallel with that of enzyme activity during the incubation with ethylene. Thus, ethylene increases the levels of the VR‐ACO1 mRNA and ACC oxidase protein as well as enzyme activity in mung bean hypocotyls. The abundance of the VR‐ACO1 transcript and protein was also induced in all parts of light‐grown mung bean seedlings by ethylene treatment. However, both the basal levels and the magnitudes of ethylene‐induction of VR‐ACO1 were markedly different in different tissues, with the roots being the most sensitive to ethylene. These results suggest that the different part of mung bean seedlings has a distinct potential to respond to ethylene with regard to ACC oxidase gene activation. Furthermore, our data suggest that the induction of VR‐ACO1 by ethylene is subject not only to transcriptional control but also to posttranscriptional control in hypocotyls, whereas ethylene regulates the VR‐ACO1 gene expression mainly at the transcriptional level in roots. The possible molecular mechanism of regulation of ACC oxidase gene expression by ethylene and its significance are discussed.