The relationship between the expression of abscisic acid biosynthesis genes, accumulation of abscisic acid and the promotion of Vitis vinifera L. berry ripening by abscisic acid

Background and Aims: Grapevines (Vitis vinifera L.) are considered to have non-climacteric fruit, but the trigger initiating ripening (veraison) is poorly understood. This study aimed to further investigate the role of abscisic acid (ABA) during berry ripening. Methods and Results: In field-grown grapes over three seasons, free ABA levels increased at veraison then subsequently declined to low levels. Bound ABA increased as the free ABA level decreased after 10–11 weeks post-flowering (wpf), but ABA must also be degraded and/or exported. The absence of a large pool of bound ABA before veraison makes it unlikely that the increase in free ABA is due to the mobilization of conjugated ABA. The expression pattern of genes crucial for ABA synthesis, zeaxanthin epoxidase and two 9-cis-epoxycartenoid dioxygenases (NCEDs) indicates that berries may have the potential to synthesize ABA in situ. However, the expression profile of these genes did not correlate well with ABA levels indicating that ABA accumulation is under more complex control. The application of (+)-ABA advanced ripening as measured by colour formation, berry size increase and to a lesser extent sugar accumulation and altered the expression of one of the NCED genes. Conclusions: The changes in berry ABA levels around the time of veraison, which influence the timing of ripening, are under complex developmental control. Significance of the Study: The improved understanding of the control of berry ripening is vital to attempts to successfully manipulate this process.