Wound-induced expression of ACC synthase genes in etiolated Mung bean Hypocotyls

Abstract

After wounding the intact tissues of developing etiolated mung bean hypocotyls, we investigated how the expression of all known members of the ACC synthase gene family was effected. Of the seven members, transcripts of only VR-ACS1, VR-ACS6, and VR-ACS7 were detectable in the control (non-stressed) hypocotyls, and their activities were strongly correlated with growth rate. In addition, expression of both VR-ACS1 and VR-ACS6 was stimulated by wounding, reaching a peak after about 1 h and sustaining that effect for about 6 h. This induced response did not occur with 5-d-old seedlings, in which transcripts were not normally detected at that stage. When auxin activity and transport were blocked by co-treatment with two inhibitors, TIBA and PCIB, the expression of those two genes was significantly reduced. However, when seedlings were co-treated before being injured, the effect of wounding was not substantially altered. Our results suggest that expression of these two ACC genes in non-stressed hypocotyls is regulated by the endogenous level of auxin. Likewise, transcripts of those genes are stimulated both by wounding and by treatment with auxin, although the two signal transduction pathways are partially independent.