Investigating the relationship between reserve nitrogen and carbohydrates on initial grapevine growth and development and the role of root derived cytokinins

The predominant cytokinin forms in the xylem sap were highly correlated with shoot growth rates conforming with the general conclusion that cytokinins control shoot growth. However, no correlations occurred between cytokinin in the xylem sap and carbohydrate or nitrogen reserves in the root or wood. By contrast, Shiraz vines exposed to a root-zone temperature of 23°C (Chapter 3) had higher bleeding sap cytokinin delivery rates and also greater shoot biomass at the time of flowering compared to vines exposed to 13°C from increased mobilisation of root starch reserves. Furthermore, in Chapters 4 and 5, vines with high starch concentrations at budbreak had higher cytokinin concentrations within the bleeding sap than vines with low starch concentrations. These results conform with this conclusion suggesting that CK loading into the sap at budbreak signals the carbohydrate level or the carbohydrate mobilisation potential of the perennial tissue to the developing shoots.