Poster: Vegetative Development
Abs #
415: Role of auxin in apical dominance: auxin repressed the expression of PsIPT
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Presenter: |
Tanaka, Mina , i014011m@mbox.media.nagoya-u.ac.jp |
Authors | Tanaka, Mina (A) Takei, Kentaro (B) Sakakibara, Hitoshi (B) Mori, Hitoshi (A) | | Affiliations: |
(A): Nagoya University
(B): Plant Science Center, RIKEN
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Apical dominance is a phenomenon in which a terminal bud inhibits the outgrowth of axillary buds. Auxin, derived from apical buds, transports basipetally in the stem and does not transport into axillary buds, implying that auxin acts in the stem or nodes, not in axillary buds. Based on this idea, we screened the genes that were specifically expressed in the second node before or after decapitation in pea. We identified a cDNA encoding isopentenyltransferase as the gene specifically expressed in the stem after decapitation, named PsIPT. Isopentenyltransferase is the key enzyme in cytokinin biosynthesis. Northern blot analysis indicated that PsIPTwas expressed in the second nodes and in the stem 1cm above the second nodes 1h after decapitation, suggesting that PsIPT was induced by the decrease of IAA because auxin transports at 1cm/h. PsIPT was expressed in the segments incubated in auxin free medium, but not those incubated in 10-5M IAA. Furthermore, PsIPT expression was repressed by application of 1% IAA lanolin paste onto the stump, but not by application of lanolin alone. These results indicated that auxin repressed PsIPT expression. We measured endogenous cytokinin content before and after decapitation. Cytokinin content in the stem and axillary buds was increased 6h after decapitation, although PsIPT was not expressed in axillary buds after decapitation, suggesting that cytokinin was derived from stem. This increase was observed in the stem as well as in the segments in which IAA was depleted, suggesting that cytokinin is biosynthesized in the stem after decapitation. These results suggest that the role of auxin in apical dominance is to repress PsIPT expression rather than to inhibit axillary bud outgrowth.
