Application of exogenous cytokinin regulates cytokinin oxidase and antioxidant activity to maintain chlorophyll pigment during ripening of banana fruit

Banana fruit ripening is accompanied by changes in activity of chlorophyll degradation. Herein, the application of exogenous cytokinin of forchlorfenuron (CPPU) to delay the ripening process by retarding degradation of chlorophyll was investigated. The changes in peel color, hue angle, chlorophyll fluorescence, and chlorophyll content were significantly inhibited by exogenous application of cytokinin. Content of endogenous cytokinin of t-zeatin was maintained and the increase of cytokinin oxidase (CKX) activity was retarded. Similar change trends were verified in the isolated peel tissues treated with CPPU. Relative expression level of the genes involved in cytokinin synthesis (MaIPT1/12) were upregulated, and CKX-related (MaCKX1/12) and chlorophyll degradation-related catabolism (MaPAO1, MaCLH1, MaSGR1, MaRCCR1, and MaRCCR12) were downregulated during storage. In addition, the scavenging activity of free radicals and membrane integrity were stabilized. Application of exogenous cytokinin of CPPU was proposed to competitively inhibit CKX activity to maintain endogenous cytokinin level, which further delayed chlorophyll degradation during banana fruit ripening.