Ontogenetic Changes in the Transport of Indol-3yl-acetic Acid into Maize Roots from the Shoot and Caryopsis

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Abstract
The quantities of endogenous IAA in endogenous in endosperms and scutella of 6-day-old maize seedlings were determined by a fluorimetric method. Endosperms were found to contain 33.4 ng IAA per plant, and scutella 7.5 ng IAA per plant. [5-3H]IAA applied to endosperms of 6-day-old seedlings moved into the roots and radioactivity accumulated at the apex of the primary root within 8 h. Two- to 7-day-old seedlings were treated simultaneously with [5-3H]IAA in the endoserpm and [2-14C]IAA on the shoot apex. The patterns of transport into the root changed during ontogeny: in successively older plants, transport from the shoot into the roots increased relative to transport from the endosperm into the roots. The auxin required for the growth of maize roots could, therefore, partially be contributed by the shoot and endosperm. Ontogenetic changes in the relative importance of these 2 supplies could be of significance for the integration of growth and development between shoot and root.