Cytokinins are implicated in keeping green kiwifruit green

Kiwifruit species that have either green flesh (Actinidia deliciosa ‘Haywood’) or gold flesh (A. chinensis ‘Hort 16A’) at harvest provide an interesting comparative system to investigate the mechanism of degreening in ripening fruit. Pilkington et al. find that fruit of both species have elevated levels of cytokinins during ripening, yet only the green kiwifruit has elevated expression of genes coding for cytokinin synthase. Additionally, high levels of O-glucosylated cytokinins are detected only in green kiwifruit, as is also the case for the expression of the gene for zeatin O-glucosyltransferase, an enzyme responsible for glucosylating cytokinins. The results strongly suggest that the green fruit are perceiving cytokinin whereas the gold fruit are not.