Carbohydrate metabolism during fruit development in sweet pepper (Capsicum annuum) plants

Abstract

Growth, accumulation of sugars and starch, and the activity of enzymes involved in sucrose mobilization were determined throughout the development of sweet pepper fruits. Fruit development was roughly divided into three phases: (1) an initial phase with high relative growth rate and hexose accumulation, (2) a phase with declining growth rate and accumulation of sucrose and starch, and (3) a ripening phase with no further fresh weight increase and with accumulation of hexoses, while sucrose and starch were degraded. Acid and neutral invertase (EC 3.2.1.26) were closely correlated to relative growth rate until ripening and inversly correlated to the accumulation of sucrose. Acid invertase specifically increased during ripening, concurrently with the accumulation of hexoses. Sucrose synthase (EC 2.4.1.13) showed little correlation to fruit development, and in periods of rapid growth the activity of sucrose synthase was low compared to the invertases. However, during late fruit growth sucose synthase was more active than the invertases. We conclude that invertase activities determine the accumulation of assimilates in the very young fruits, and a reactivation of acid invertase is responsible for the accumulation of hexoses during ripening. During late fruit growth, before ripening, sucrose synthase is transiently responsible for the sucrose breakdown in the fruit tissue. Results also indicate that pyrophosphate‐dependent phosphofructokinase (EC 2.7.1.90) and its activator fructose‐2,6‐bisphosphate (Fru2,6bisP) are involved in the regulation of the sink metabolism of the fruit tissue.

Repression of both isoforms of disproportionating enzyme leads to higher malto-oligosaccharide content and reduced growth in potato

“…The samples were incubated at 4°C for 30 min and centrifuged at 3,890g for 3 min at 4°C. Part of the supernatant (75 l) was adjusted to pH 7 and the content of sugars was determined by the method of Nielsen et al (1991). The remaining supernatant (50 l) was analysed for MOS by adding 30 l 2 M KOH, 0.4 M Mes pH 5.6, 0.4 M KCl.…”

Upregulation of pyrophosphate: fructose 6-phosphate 1-phosphotransferase (PFP) activity in strawberry

“…Some insight has however, been gained by investigating sugar accumulation patterns and PFP activity in heterotrophic tissues. An inverse correlation was observed between PFP activity and sucrose accumulation in sugarcane stalks (Whittaker and Botha 1999), while hexose content and PFP activity is inversely correlated in sweet pepper fruit (Nielsen et al 1991). In wild-type strawberry, activity patterns of PFP and FBPase were similar during ripening, while PFK activity remained relatively constant (Basson et al 2010 While these correlations support the view that PFP plays a role in heterotrophic carbon metabolism, the role of PFP in sugar-accumulating heterotrophic tissues, such as fruit, is not clear.…”

Cytokinins and leaf development in sweet pepper (Capsicum annuum L.)

“…In sweet pepper, Nielsen and Veirskov (1990) have demonstrated that within a leaf a gradient in expansion rate exists, with the highest rates of area expansion in the leaf base. Changes in levels of fructose-2,6-bisphosphate and rates of area expansion were furthermore accompanied by dramatic changes in activities of enzymes essential to sink and source metabolism of the leaf tissue (Nielsen 1990). Fructose-2,6-bisphosphate is generally held to promote glycolytic metabolism (Black et al 1987) although this is still a matter of controversy (Stitt 1990).…”

“…As pepper has recently been characterized with respect to the regulation of carbon allocation during both leaf (Nielsen and Veierskov 1990;Nielsen 1990) and fruit growth (Nielsen et al 1991) it provides a useful system for this endeavor. The sink-strength hypothesis for cytokinin action should be tested taking both uptake and utilization of carbohydrates into account.…”