-Introduction. Consumers and processors value tomatoes with high fruit sugar content; however, most breeding and cultural practices negatively impact this trait. Wild tomato species can accumulate two-to three-fold more fruit sugar than cultivars and are proving to be valuable both as a source of high-sugar loci to broaden the genetic base of currently produced cultivars, and as research material to understand this trait. Synthesis. While cutting-edge genomic approaches have taught us much about fruit phenotypes, it is still important to assess fruit enzyme activities and metabolic fluxes in lines with contrasting fruit sugar accumulation. These metabolic functions are closest to the ripe fruit sugar trait. In this review, we focus our attention on the biochemical pathways, especially starch biosynthesis, that may influence tomato fruit sugars. We try where possible to put this information into a physiological context because together they influence yield. We compare and contrast sugar metabolism in cultivars and wild tomato species and identify factors that may influence differences in their fruit size. Conclusion. Although difficult, we show that it is possible to develop fruit with high horticultural yield and use the breeding line 'Solara' as an example. In addition, we suggest avenues of further investigation to understand the regulation and control of fruit carbohydrate content. USA / Solanum lycopersicum / fruits / sugars / carbohydrate metabolism / carbohydrate contentFacteurs biochimiques contribuant à la teneur en sucre des fruits de tomate : une revue.Résumé -Introduction. Les consommateurs et les industriels apprécient les tomates avec un fort taux en sucres, mais la plupart des pratiques culturales et d'amélioration ont un impact négatif sur ce caractère. Les espèces de tomate sauvage peuvent accumuler 2 ou 3 fois plus de sucres dans le fruit que des cultivars et elles s'avèrent précieuses à la fois comme une source de loci à haute teneur en sucres pour élargir la base génétique des cultivars actuellement produits, et comme matériel de recherche pour comprendre ce caractère. Synthèse. Alors que les approches génomiques de pointe nous ont appris beaucoup sur le phénotype des fruits, il reste important d'évaluer l'activité des enzymes de fruits et les flux métaboliques dans des lignées présentant des situations contrastées d'accumulation de sucres dans les fruits. Ces fonctions métaboliques sont les plus proches du caractère de teneur en sucres dans le fruit mûr. Dans cette synthèse, nous nous sommes focalisés sur les voies biochimiques, en particulier sur la biosynthèse de l'amidon qui peut influencer les sucres dans le fruit des tomates. Nous essayons autant que possible de mettre cette information dans un contexte physiologique car, ensemble, ils influencent le rendement. Nous comparons et mettons en contraste le métabolisme des sucres dans les cultivars et les espèces sauvages de tomate et nous identifions les facteurs qui peuvent influencer des différences de taille des fruits. Conclusio...

The physicochemical properties of starch from tomato (Solanum lycopersicum L.) pericarp and columella of cv. Moneymaker fruit at 28 days post anthesis (DPA) were investigated, providing the first description of the composition and structure of tomato fruit starch. Starch granules from pericarp were mainly polygonal, 13.5-14.3 microm, and increased in size through development, being largest in ripening fruit. Amylopectin content was 81-83% and was of molecular weight 1.01 x 10(8) g/mol; the phosphorus content was 139 ppm, and starch showed a C-type pattern with crystallinity of 30%. Starch characteristics were similar in columella except granule size (16.8-17.8 microm) and crystallinity (40%), although 6-fold more starch accumulated in the pericarp. Solara, a high-sugar tomato cultivar, was also studied to determine if this affects starch granule architecture. There were few differences from Moneymaker, except that Solara columella starch crystallinity was lower (26%), and more starch granule-intrinsic proteins could be extracted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Starch is transiently accumulated in tomato fruit with near complete degradation achieved by maturity. Surprisingly, (14)C-pulse-chase analyses indicated that the rate of starch degradation was highest in immature fruit [10 days post anthesis (DPA)] when maximal synthesis occurs, but was almost undetectable at 45 DPA when there is net breakdown of starch. Further analysis of starch accumulation, rate of synthesis, particle size analysis, and confocal laser scanning microscopy of starch granules from developing fruit suggests that the rate of starch degradation does increase after 40 DPA, but it may not occur at the same site at which starch is synthesized. Furthermore, the degradation rate at maturity is lower than that measured in early development. Overall, the results suggest that starch degradation in developing tomato is biphasic with separate regiotemporal occurrences. This mechanism may have evolved to offer flexibility in balancing starch accumulation and utilization in the developing fruit.

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