The Role of Auxin in the Apical Regulation of Leaf Abscission in Cotton (Gossypium hirsutumL.)

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Abstract
The petiole abscission induced by deblading cotyledonary leaves of cotton (Gossypium hirsutum L. cv. Delta Pine) was accelerated by the presence of the intact shoot apex or, in decapitated plants and explants, by application to the stem (proximal application) of indol-3yl-acetic acid (IAA) or 1-aminocyclopropane-l-carboxylic acid (ACC). IAA and ACC accelerated the abscission of debladed petioles whether applied above or below the cotyledonary node. Transport of IAA to the node was not required for the response to proximal IAA. [2,3-14C]ACC was readily transported to the nodal region whether applied to the stem above or below the node. Application of IAA or ACC to the stem did not induce the abscission of intact leaves or of debladed petioles treated distally with IAA The acceleration of abscission by proximal IAA, but not that caused by ACC, was prevented if explants were treated with a-aminooxyacetic acid (AOA), an inhibitor of ACC-synthase. AOA also prevented the acceleration of abscission caused by the shoot apex. The progress of abscission in debladed explants was greatly delayed by silver thiosulphate (STS—an inhibitor of ethylene action), whether or not the explants were treated with IAA or ACC. It is suggested that the speeding effects of the shoot apex and of proximal auxin on the abscission of debladed petioles requires auxin-induced ACC synthesis. The possibility is discussed that ACC may function as a mobile abscission promoter

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