Starch is an important component of a wheat grain, comprising 50-70% of its dry weight. Its biosynthesis involves a complex pathway mediated by several enzymes, each of which is encoded by genes that have more than one family member. To better understand starch synthesis in wheat grains, this study characterized the sucrose-starch metabolic pathway using physiological, molecular, biochemical and metabolic approaches. These analyses led to the identification of genes that appear to have predominant expression during grain development in wheat including, TaSUT1, TaSuSy2, AGPL1, SSI, SSIIIa and SBEIIa, suggesting that these genes play a regulatory role in starch accumulation. This was further confirmed by comparative analyses of starch synthesis between cultivars with contrasting thousand kernel weights, which revealed a closer association of the expression of the same set of genes with starch accumulation in developing wheat grains. The effect on starch yield of one of the candidate genes identified, AGPase, was examined through a transgenic approach, which involved expression of a gene encoding modified version of maize AGPase large subunit, designated as Sh2r6hs, in wheat under the control of maize’s constitutive Ubiquitin1 promoter. This manipulation of the wheat AGPase activity produced wheat lines with increased AGPase activity, grain weight and grain starch level, suggesting that the wheat grain size can be enhanced through increasing the capacity of starch synthesis both in the source and sink tissues. The study also identified and characterized a partial fragment of wheat rbcS promoter, and indicated that the promoter fragment can potentially be used as a tool for targeting the expression of genes of interest in photosynthetic source tissues. / October 2014

Während der Entwicklung von Früchten der Tomate (Sorte Micro-Tom) wurde der Kohlenhydrat-Stoffwechsel untersucht. Es wurde ein Unterschied zwischen dem Metabolismus im Perikarp und dem des Plazenta-Gewebes gefunden. Stärke wurde in der Plazenta langsamer abgebaut als im Perikarp, während lösliche Zucker im Perikarp stärker akkumulierten. Die Aktivitäten der glykolytischen Enzyme tendierten zu einem Maximum 40 Tage nach der Blüte. Weiterhin wurde die Expression einiger plastidärer Transporter untersucht. Sowohl der Triosephosphat-Tranporter (TPT) als auch der Glucose-6-phosphat-Transporter wurden am stärksten in grünen Früchten exprimiert, während der Reife nahm die Expression ab. Der ATP/ADP-Transporter wurde während der Fruchtentwicklung nur schwach exprimiert.Es besteht die Hypothese, daß die Rolle der drei Enzyme plastidäre Fructose-1,6-Bisphosphatase (cp-FBPase), ADP-Glucose Pyrophosphorylase (AGPase) und Glucan Wasser Dikinase (GWD) darin besteht, die Stärke-Akkumulation in der frühen Entwicklung der Tomaten-Frucht zu beeinflussen. Diese Hypothese wurde unter Verwendung der Antisense-Technik für die plastidären FBPase (unter der Kontrolle des B33 Promoters), sowie für die AGPase und die GWD (beide unter der Kontrolle des CaMV 35S-Promoters) in der Tomaten-Kultivar Moneymaker untersucht. Die Repression von plastidärer FBPase oder AGPase in der Frucht der Tomate scheint die Metaboliten-Konzentrationen nicht so stark wie in den Blättern zu beeinflussen. Der Grund hierfür ist wahrscheinlich, daß jede Veränderung durch die Fähigkeit der Frucht, Zucker zu importieren, abgepuffert wird. Auf der anderen Seite hatte die Repression des GWD Proteins in der Frucht der Tomate starke Effekte auf die Metaboliten-Konzentrationen. / Carbohydrate metabolism was studied during the development of fruits of the tomato cultivar Micro-Tom. The metabolism of the pericarp and placental tissues was found to be different. Starch being degraded more slowly in the placenta than in the pericarp, while soluble sugars accumulated to a greater extent in the pericarp. The activities of glycolytic enzymes tended to peak at 40 days after flowering. The expression of some plastidial transporters was also studied. Both the triose phosphate transporter (TPT) and Glucose-6-Phosphate (Glc-6-P) transporter were expressed greatest in green fruits, before declining. The expression of the triose phosphate transporter (TPT) was greater than that of Glc-6-P transporter. The ATP/ADP transporter was expressed to a low level throughout fruit development. The role of three enzymes Chloroplastic Fructose-1,6-bisphosphatase (cp-FBPase), ADP-glucose Pyrophosphorylase (AGPase) and Glucan Water Dikinase (GWD) protein are thought to influence the accumulation of starch in early development in tomato fruit were studied in normal sized tomatoes of the cultivar Moneymaker using antisense technique under the control of the patatin B33 promoter in the case of cp-FBPase, and the CaMV 35S promoter in the case of AGPase and GWD protein. It appears that repression of cp-FBPase and AGPase in tomato fruits does not influence metabolite levels as greatly as it does in leaves, possibly because any alterations are buffered by the ability of the fruit to import sugars. On the other hand, the repression of GWD protein in tomato fruits has a strong effect on metabolite levels.