Regulation of Ethylene Biosynthesis in Response to Pollination in Tomato Flowers

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Abstract
Pollination of many flowers leads to an increase in ethylene synthesis and flower senescence. We have investigated the regulation of pollination-induced ethylene synthesis in tomato (Lycopersicon esculentum) using flowers of the dialytic(dl) mutant, in which pollination can be manipulated experimentally, with the aim of developing a model system to study tomato flower senescence. Ethylene synthesis increased rapidly indl pistils following pollination, leading to accelerated petal senescence, and was delayed in ethylene-insensitiveNever-ripe (Nr) pistils. However,Nr pistils eventually produced more ethylene thandl pistils, suggesting the presence of negative feedback regulation of ethylene synthesis following pollination.LEACS1A expression correlated well with increased ethylene production in pollinated dl pistils, and expression in Nr revealed that regulation is via an ethylene-independent mechanism. In contrast, the induction of the 1-aminocyclopropane-1-carboxylic acid oxidases, LEACO1and LEACO3, following pollination is ethylene dependent. In addition, the expression profiles of ACS andACO genes were determined during petal senescence and a hypothesis proposed that translocated 1-aminocyclopropane-1-carboxylic acid from the pistil may be important for regulating the initial burst of ethylene production during petal senescence. These results are discussed and differences between tomato and the ornamental species previously studied are highlighted.