Functional uncoupling of the tonoplast proton pump and its effect on the flesh gelling physiological disorder in papaya fruit

Abstract A physiological pre-harvest disorder known as flesh gelling has been verified in the ‘Golden’ papaya culture in the main papaya-producing regions of Brazil. While this disorder has been described in the literature, its cause has not been identified yet. There is evidence in other works which associated papaya gelling with cell plasmolysis in fruit tissue. The primary system of ion and sugar transport by proton pump enzyme activity of papaya fruit was investigated in this work and may help identify the cause of this disorder. A reduction in the P-ATPase activity of flesh gelling pulp was verified, which was more evident in the activity of ATP hydrolysis than in the H + transport. On the other hand, the V-ATPase exhibited a strong increase in its ATP hydrolysis activity, but completely uncoupled to the H + pumping capacity, which markedly decreased compromising the establishment of the ATP-dependent proton gradient in tonoplasts of flesh gelling fruits. Our results indicated a drop in cellular capacity for sugar and ion compartmentalization and water retention in cells, which could be the cause of cell plasmolysis and the soaked tissue appearance, among other alterations observed in the flesh gelling disorder.