Autoinhibition of indoleacetic acid transport in the shoots of two-branched pea (Pisum sativum) plants and its relationship to correlative dominance

Two-branched pea plants (Pisum sativum L. cv. Lisa ZS) with different dominance degrees, obtained by removing the epicotyl shortly after germination, were used to study the interaction between the polar transport of indoleacetic acid (IAA) in both branches of the plants and its relationship to correlative dominance. The dominant shoot had higher transport capacity for H-3-IAA, exported more IAA out of its apex and possessed more endogenous IAA in apex and the first internode than the dominated one. Decapitation of the dominant shoot resulted in a rapid resumption of growth in the dominated shoot, accompanied by a considerable increase in its capacity to export endogenous IAA and to transport H-3-IAA. Parallel experiments with intact two-branched plants and Y-formed explants showed that the H-3-IAA transport on one side was inhibited by the other branch apex or by pre-application of C-12-IAA to the cut stump of the decapitated side. The higher the concentration of C-12-IAA applied to the cut stump of one side of the Y-form explant was used, the stronger the H-3-IAA transport was inhibited and the more the transported IAA was conjugated above the junction on the other side. The results of these experiments support the autoinhibition hypothesis at junctions. The relationship between elongation growth and IAA export/transport in the two-branch pea plants is considered.