Short-term stimulation of growth induced by the apical application of IAA to intact maize [Zea mays] coleoptiles
1996
Iino, M. (Osaka City Univ. (Japan). Faculty of Science)
Indole-3-acetic acid (IAA), mixed with lanolin, was applied to the surface of defined parts of the intact coleoptile of maize (Zea mays L.) seedlings, and the elongation growth of the coleoptile zone was monitored for a period of 8 h. When IAA was applied to a subapical region, the growth of zones located below was stimulated only temporarily, although stimulation was continuous when IAA was applied directly to the zone that was monitored for growth. This short-term stimulation was observed at all concentrations tested (0.03-30 mg of IAA per g of lanolin). The duration of stimulated growth, which varied from 1 to 5 h, was longer as the distance from the site of IAA application was reduced and the concentration of IAA was increased. Growth during the post-stimulation phase after application of a high does of IAA could not be enhanced again by applying IAA near the site of the first application, but it was enhanced when IAA was applied directly to the zone used to measure growth. These results suggest that the supply of IAA from the site of application to lower zones is controlled internally such that the elevated concentration of IAA in these zones returns to the concentration before IAA application. Either the feedback regulation of auxin transport or the feedforward regulation of auxin metabolism may account for the suggested control of IAA supply
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