Abstract
Cucumber seedlings form a specialized protuberance, called peg, on the transition zone between the hypocotyl and the root. When cucumber seeds germinate horizontally, a peg develops on the lower side of the transition zone. Auxin and mRNA of auxin-inducible CsIAA1 gene accumulate more abundantly on the peg-formed lower side than the peg-suppressed upper side of the transition zone. In contrast, mRNA of auxin-repressed CsGRP1 gene accumulates more abundantly on the upper side than the lower side. To verify the importance of auxin action in the peg formation, we investigated the effect of anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), on peg formation. PCIB inhibited peg formation and accumulation of CsIAA1 mRNA on the lower side of the transition zone. Accumulation of CsGRP1 mRNA was accelerated in the lower side of the PCIB-treated transition zone. These results suggest that auxin plays an essential role in peg formiation via auxin-regulated gene expression.
