Abstract
Auxin is a plant hormone that regulates diverse aspects such as tissue elongation, tropic growth, embryogenesis, apical dominance, lateral root initiation, vascular differentiation, and fruit development. Recently, the ubiquitin-ligase complex SCFTIR1, including the TIR/ABF auxin-receptor family, was demonstrated to be critical for auxin-mediated transcriptional regulation. In contrast, early-phase auxin-induced cell expansion, as explained by the acid-growth theory, was observed to occur without this system. To clarify the molecular mechanism by which auxin induces cell expansion we developed the experimental system for analyzing auxin-induced elongation with hypocotyls of a model plant Arabidopsis. In our experimental system we used the hypocotyl segments excised from etiolated Arabidopsis seedlings to deplete the endogenous auxin. When applied to the isolated hypocotyl segments, exogenous auxin induced hypocotyl elongation after a lag phase of around 10 minutes. Furthermore we will discuss a possible mechanism of auxin-acid-growth demonstrated by the biochemical and pharmacological analyses of the auxin-induced hypocotyl elongation.
