The green-fruited Lycopersicon hirsutum Humb. and Bonpi. The green fruited, wild Lycopersicon species (subspecies Eriolycopersicon) has been reported to contain high levels of sucrose, as compared with the red-fruited (Eulycopersicon) species, which contains primarily glucose and fructose in the mature fruit, with only trace amounts of sucrose (4). The species that accumulate sucrose are characterized by high TSS2 content ('Brix) and are of potential importance in improving fruit quality of cultivated Lycopersicon esculentum '

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, 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

The carbohydrate economy of developing tomato fruit is determined by wholeplant source–sink relationships. However, the fate of the imported photoassimilate partitioned to the fruit sink is controlled by the carbohydrate metabolism of the fruit tissue. Within the Lycopersicon spp. there exists a broad range of genetic variability for fruit carbohydrate metabolism, such as sucrose accumulation and modified ratios of fructose to glucose in the mature fruit and increased starch synthesis in the immature fruit. Metabolic pathways of carbohydrate metabolism in tomatoes, as well as natural genetic variation in the metabolic pathways, will be described. The impact of sink carbohydrate metabolism on fruit non-structural carbohydrate economy will be discussed.