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

The concentration of reducing sugars in the developing firstinflorescence of the tomato (Lycopersicon esculentum Mill.)increased steadily between the macroscopic appearance of theflower buds and the initial stages of fruit expansion. Overthis period sucrose concentrations remained relatively constant.The rise in reducing sugar concentration was accompanied byan increase in the activity of an acid invertase. In individualflower buds invertase activity rose to a maximum shortly beforeanthesis and declined sharply as the anthers dehisced. Increased planting densities and removal of source leaves reducedthe rate of dry matter accumulation by the first inflorescenceand increased the incidence of flower bud abortion. These changeswere 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 increasedthe relative growth rate of the inflorescence and led to a substantialincrease in its invertase content. These treatments had relativelylittle effect on sucrose concentration in the inflorescence. The data are consistent with the operation of an invertase-mediatedunloading mechanism for transported sucrose at sinks in theflower buds. It is suggested that the retarded development ofthe first inflorescence and the high incidence of flower budabortion observed under conditions of reduced photoassimilateavailability are causally related to the decline in invertaseproduction in the flower buds. Possible mechanisms for the regulationof invertase synthesis in the flowers are discussed. Lycopersicon esculentum Mill, tomato, inflorescence development, invertase, sink activity