Carbohydrate metabolism in ripening banana and its alteration on gamma irradiation in relation to delay in ripening

Abstract

Ripening, of climacteric class of fruits like banana, is accompanied with an upsurge in respjration- indicating a change in metabolism from hexose rnonophosphate shunt pathway to glycolytic pathway. The key enzyme in glycolytic pathway, namely, phosphofructokinase, is activated and this activation paralleled with the increase in respiration rates. The enhancement in the activity of enzymes of glycolytic and Kreh's cycle help the fruit to assimilate energy as ATP produced from the breakdown and oxidation of storage starch. The demand for energy supply is great for the different ripening processes.

Gamma irradiation of the fruit at the preclimacteric stage delayed the onSet of climacteric to about 7 to 9 days, thereby extending the ripening to 15-20 days. This delay was brought about by the alterations in the metabolism of carbohydrate. There is a predominance of HM P pathway in irradiated banana. This along with the activation of phosphatases like FDPase and F-6-Pase restricted the entrance of sugar phosphate esters to Kreb's cycle for oxidation. The functioning of Kreb's cycle is also affected by the inhibition of succinic dehydrogenase. But activation of glyoxylate shunt pathway helped to maintain the levels of KIeb's cycle intermediates like citrdte and malate, although energy production is reduced. Finally the activation of glueoneogenic pathway helps. in channelling the metabolities back to sugars. All these metabolic changes cause a considerable depletion in the production of ATP.