Wound-Induced Expression of ACC Synthase Genes in Etiolated Mung Bean Hypocotyls

After wounding the intact tissues of developingetiolated mung bean hypocolyls, 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-ACSl and VR-ACS6 was stimulated by wounding, reaching a peak after about 1 h and sustaining that effect or about 6 h. This induced response did not occur with 5-d-old wedlings in which transcripts were not normally detected at that stage. When auxin activily and transport were blocked hy co-treatment with two inhibitors, TIBA and PCIB, the expression of those two genes was significantly reduced. Huwever, 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.