Increase in Cytokinin Levels during Ripening in Developing Vitis vinifera cv. Shiraz Berries

Abstract

We describe the quantification of the phytohormone abscisic acid and its metabolites and a range of cytokinins and gibberellic acid species in the same grape (Vitis vinifera L.) berry pericarp developmental series. Some relatively minor differences in concentrations were observed for some abscisic acid metabolites and gibberellic acids when compared to previous studies. The biologically active gibberellic acids 4 and 7 (along with precursor and inactive forms) were present before veraison but at very low concentrations after veraison. Abscisic acid levels peaked shortly after veraison, but high levels of dihydrophaseic acid before veraison and high levels of abscisic acid glucose ester after veraison suggest that two different catabolic pathways are developmentally controlled. The analysis of the concentrations of certain cytokinins provided some previously unreported and surprising results, as the concentration of isopentenyladenine increased rapidly at veraison and remained at elevated levels throughout ripening. The reason for this phenomenon is unknown, but a similar increase in the concentrations of some cytokinins has been observed during kiwifruit development and may be involved in the control of ripening and/or senescence.