Modification of Carbohydrate Content in Developing Tomato Fruit

The carbohydrate content of the tomato fruit is a major determinant of the quality and value of the crop, whether it be for the fresh produce market or for processing.Soluble sugar levels contribute strongly to the soluble solids content and to tomato flavor (Stevens et al., 1977a(Stevens et al., , 1977b) ) and, therefore, increasing these levels has been the goal of many research efforts.The carbohydrate economy of developing tomato fruit is determined by the whole gamut of plant source-sink relationships.These include photoassimilate production at the source, its partitioning within the leaf, transport and export to alternative sinks and, finally, import into and metabolism within the fruit sink.Although the carbohydrate status of the fruit is a product of the interactions among all these processes, the fate of imported photoassimilate partitioned to the fruit is controlled only by the carbohydrate metabolism in the fruit itself.Clearly, fruit carbohydrate content can be increased by improving the source contribution to the carbohydrate economy.This can be seen, for example, in the effects on fruit total soluble solids (TSS) content of: light intensity; plant architecture modifications, such as by pruning; or genetic control of growth habit (sp gene) (see Davies and Hobson, 1981).The same is likely to apply to the effects of the physiological components of loading, transport, and unloading processes on fruit sugar content.Recent studies of these processes in tomatoes (Ruan and Patrick, 1995;Ruan et al., 1997) should help to set the stage for the