Abstract
Cucumber seedlings develop a peg on the concave side of the bending transition zone (TR zone) between hypocotyl and root. We have previously shown that gravistimulation causes asymmetrical mRNA accumulation of auxin-inducible genes (CS-IAA1 and CS-IAA2) in TR zone when peg initiation occurs. To reveal the molecular mechanism of these genes expression, we examined the localization of mRNAs of auxin response factors (CS-ARFs) during peg formation by in-situ hybridization and compared them with that of CS-IAA mRNAs. In 18-h-old seedlings CS-ARF2 mRNA, as well as CS-IAA1 mRNA, accumulated in epidermal, cortical and vascular tissues of TR zone. In contrast, 24-h-old seedlings accumulated more CS-IAA1 mRNA on the concave side of TR zone than on the convex side, but no asymmetric mRNA localization of CS-ARFs was detected. These results suggest that CS-ARF2 activates CS-IAA1expression during peg formation in cucumber seedlings, and auxin directly or indirectly modulates its transcriptional activity.
