Abstract
When cucumber seeds are placed in a horizontal position for germination, the resulting seedlings develop a specialized protuberance, termed the peg, on the lower side of the transition zone between the hypocotyl and the root, due to gravistimulation. We have shown that auxin induces peg formation and that mRNA of auxin-inducible CsIAA1 gene in epidermis and cortex accumulates more abundantly in the lower side of the transition zone. In this study, we investigated auxin distribution in the transition zone by immunohistochemical analysis. By double staining with anti-auxin monoclonal antibody and DAPI, auxin signals were detected mainly in nuclei, and those in epidermis and cortex of the lower side were stronger than those of the upper side. These results suggest that differential accumulation of auxin in nuclei between the lower side and the upper side of the transition zone is involved in unilateral placement of peg formation in cucumber seedlings.
