THE EFFECT OF GLUCOSE ON THE CONTROL OF CARBOHYDRATE-METABOLISM IN RIPENING BANANAS

The effect of exogenous glucose on the major fluxes of carbohydrate me tabolism in cores of climacteric fruit of banana (Musa cavendishii Lam b ex Paxton) was determined with the intention of using the effects in the application of top-down metabolic control analysis. Hands of bana nas, untreated with ethylene, were allowed to ripen in the dark at 21 degrees C. Cores were removed from climacteric fruit and incubated in 100 or 200 mM glucose for 4 or 6 h. The rates of starch breakdown, suc rose and fructose accumulation and CO2 production were measured. The s teady-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-C-14]-, [1-C-14]-, [3,4-C -14]- and [6-C-14]glucose, and [U-C-14]glycerol. The data were used to estimate the major fluxes of carbohydrate metabolism. Supply of exoge nous glucose led to increases in the size of the hexose-monophosphate pools. There was a small stimulation of the rate of sugar synthesis an d a major increase in the rate of starch synthesis. Starch breakdown w as inhibited, Respiration responded to the demand for ATP by sugar syn thesis. The effect of glucose on fluxes and metabolite pools is discus sed in relation to our understanding of the control and regulation of carbohydrate metabolism in ripening fruit.