Invertase Activity, Soluble Carbohydrates and Inflorescence Development in the Tomato (Lycopersicon esculentum Mill.)

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Abstract
The concentration of reducing sugars in the developing first inflorescence of the tomato (Lycopersicon esculentum Mill.) increased steadily between the macroscopic appearance of the flower buds and the initial stages of fruit expansion. Over this period sucrose concentrations remained relatively constant. The rise in reducing sugar concentration was accompanied by an increase in the activity of an acid invertase. In individual flower buds invertase activity rose to a maximum shortly before anthesis and declined sharply as the anthers dehisced. Increased planting densities and removal of source leaves reduced the rate of dry matter accumulation by the first inflorescence and increased the incidence of flower bud abortion. These changes were correlated with reductions in reducing sugar concentrations, in reducing sugar/sucrose ratios and in acid invertase levels. Removal of young leaves at the shoot apex significantly increased the relative growth rate of the inflorescence and led to a substantial increase in its invertase content. These treatments had relatively little effect on sucrose concentration in the inflorescence. The data are consistent with the operation of an invertase-mediated unloading mechanism for transported sucrose at sinks in the flower buds. It is suggested that the retarded development of the first inflorescence and the high incidence of flower bud abortion observed under conditions of reduced photoassimilate availability are causally related to the decline in invertase production in the flower buds. Possible mechanisms for the regulation of invertase synthesis in the flowers are discussed.