title: P-chlorophenoxyisobutyric acid impairs auxin response for gravity-regulated peg formation in cucumber (Cucumis sativus) seedlings.
abstract: Cucumber (Cucumis sativus L.) seedlings form a specialized protuberance, the peg, on the transition zone between the hypocotyl and the root. When cucumber seeds germinate in a horizontal position, the seedlings develop a peg on the lower side of the transition zone. To verify the role of auxin action in peg formation, we examined the effect of the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), on peg formation and mRNA accumulation of auxin-regulated genes. Application of PCIB to cucumber seedlings inhibited peg formation. The application of indole-3-acetic acid (IAA) competed with PCIB and induced peg formation. Furthermore, application of PCIB decreased auxin-inducible CsIAA1 mRNA and increased auxin-repressible CsGRP1 mRNA in the lower side of the transition zone. The differential accumulation of CsIAA1 and CsGRP1 mRNAs in the transition zone of cucumber seedlings grown in a horizontal position was smaller in the PCIB-treated seedlings. These results demonstrate that endogenous auxin redistributes and induces the differential expression of auxin-regulated genes, and ultimately results in the suppression or induction of peg formation in the gravistimulated transition zone of cucumber seedlings.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Minobu
authors.initials: M
authors.lastname: Shimizu
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miyazawa
authors.forename: Nobuharu
authors.initials: N
authors.lastname: Fujii
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D002995:Clofibric Acid / Q000494:pharmacology*; D018553:Cucumis sativus / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006112:Gravitation; D018522:Gravitropism / Q000187:drug effects*; D007210:Indoleacetic Acids / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D013995:Time
chemical_list: D007210:Indoleacetic Acids; D002995:Clofibric Acid