Auxin Transport in the Physiology of Fruit Development

Abstract

Transport of indoleacetic acid (IAA) through the pedicel and subsequent parthenocarpy was investigated by application of solutions of nonradioactive and methylene-C14-labeled IAA to the pedicel of a variety of tomato (Lycopersicum esculentum "Pan American") which does not naturally produce seedless fruits and a variety of cucumber (Cucumis sativus "Long Green") which produces naturally both seeded and seedless fruits. The effects of gibberellic acid (GA) and nonradioactive and carbaxyl-C14-labeled 2,4-dichloro-phenoxyacetic acid (2,4-D) on parthenocarpy of tomato were compared with those of IAA. Solutions of IAA and IAA incorporated in lanolin seldom induced parthenocarpy of tomato when applied to the pedicel, but similar treatments of the ovary with IAA or applications of dilute solutions of 2,4-D or GA to the pedicel were highly effective. Distribution of radioactivity from labeled IAA supplied to tomato pedicel indicated there was little movement of IAA into the ovary and that the abscission zone blocked movement of the auxin through the pedicel. In contrast, when labeled 2,4-D was supplied to tomato pedicel, the distribution of radioactivity indicated acropetal movement through the pedicel into the ovary took place readily. Applications of IAA to cucumber pedicel were very effective in causing parthenocarpy. When labeled IAA was supplied to the pedicel, the distribution of radioactivity indicated transport of the auxin was not restricted as in tomato, and that the movement of the auxin into the ovary was sufficient to induce parthenocarpy.