The effect of glucose on the control of carbohydrate metabolism in ripening bananas

Abstract

Abstract. The effect of exogenous glucose on the major fluxes of carbohydrate metabolism in cores of climacteric fruit of banana (Musa cavendishii Lamb ex Paxton) was determined with the intention of using the effects in the application of top-down metabolic control analysis. Hands of bananas, untreated with ethylene, were allowed to ripen in the dark at 21 ~ Cores were removed from climacteric fruit and incubated in 100 or 200 mM glucose for 4 or 6 h. The rates of starch breakdown, sucrose and fructose accumulation and CO2 production were measured. The steady-state contents of hexose monophosphates, adenylates and pyruvate were determined. In addition, the detailed distribution of label was determined after supply of the following: [U-14C3-, [1-14C]-, [3,4-14C]-and [6-14C]glucose, and [U-lgC]glycerol. The data were used to estimate the major fluxes of carbohydrate metabolism. Supply of exogenous glucose led to increases in the size of the hexose-monophosphate pools. There was a small stimulation of the rate of sugar synthesis and a major increase in the rate of starch synthesis. Starch breakdown was inhibited. Respiration responded to the demand for ATP by sugar synthesis. The effect of glucose on fluxes and metabolite pools is discussed in relation to our understanding of the control and regulation of carbohydrate metabolism in ripening fruit.

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars during Grain Filling: Impact of Invertase Activity on Carbon Metabolism during Kernel Development

“…A similar observation was made in potato cells . It is believed that the continual cycling of its degradation and synthesis is one of the common features of sucrose metabolism in many plant systems Stitt 1991, 1993;Hill and Rees 1995). The enhanced activities of sucrose synthase, acid and bound invertase in the leaves of water stress of tolerant cultivar may contribute to the a rapid cycling of sucrose, thus promoting carbon partitioning in favor of sucrose accumulation for counteracting the stress condition .…”

A Mutant of Arabidopsis Lacking the Triose-Phosphate/Phosphate Translocator Reveals Metabolic Regulation of Starch Breakdown in the Light

“…However, although it is known that levels of other carbohydrates influence starch breakdown (Hill and ap Rees, 1995;Loreti et al, 2003) and that many of the genes encoding putative components of the starch degradative machinery are regulated in a circadian fashion (Harmer et al, 2000), the regulatory mechanisms determining the timing and extent of starch degradation are largely unknown. The turnover of starch in TPT-deficient plants specifically under HL conditions is likely to reflect the aberrant activation of one or more signals-starch breakdown in the light does not appear to be a normal feature of wild-type plants (Zeeman et al, 2002)-and provides a tightly controlled system within which to investigate the regulation of starch turnover.…”

Potato plants contain multiple forms of sucrose phosphate synthase, which differ in their tissue distributions, their levels during development, and their responses to low temperature

“…SPS is also present in sink tissues, where it may have additional roles. It is involved in a cycle of sucrose degradation and resynthesis that contributes to the regulation of sucrose import and mobilization (Dancer, Hatzfeld & Stitt 1990;Wendler et al 1990;Geigenberger & Stitt 1991, and developmental processes such as fruit ripening (Hubbard, Pharr & Huber 1990;MacRae et al 1992;Hill & apRees 1995). Further, sucrose is synthesized in response to environmental stresses, including water deficit (Morgan 1984;Quick et at.…”