Abstract

Peach (Prunus persica) fruits have a sigmoidal growth pattern that is regulated by plant hormones, including cytokinin. After floral bloom, there is an exponential growth phase that is associated with high endogenous cytokinin levels and an increase in pericarp cell division. Subsequently, the endocarp lignifies, endogenous cytokinin levels decrease and pericarp growth rate is reduced. A second exponential growth phase follows the lignification stage. Then, an increase in ethylene triggers fruit ripening. In order to determine the molecular and physiological effects of cytokinin on peach fruit, exogenous application was performed in both field and laboratory settings. Transcriptomic analyses of peach fruits treated exogenously with cytokinin (trans-zeatin) in a laboratory setting, at different stages of fruit development, revealed a higher number of cytokinin responsive genes in the lignification stage of development, as well as a significant change in genes associated with ethylene biosynthesis and perception during the fruit ripening stage. Field applications of cytokinin (Thidiazuron) revealed a significant increase fruit harvest size, increases in chlorophyll post-lignification, changes in fruit color and a delay in harvesting time. These laboratory and field studies suggest that cytokinin participates negatively in fruit ripening by altering ethylene synthesis and perception.