Cytokinin and Carbohydrate Changes During Flowering of Boronia megastigma

Boronia megastigma, a native Australian shrub, requires 10-12 weeks of low temperatures to initiate flowers and commit them to develop through to anthesis. Our understanding of the environmental control of flowering of B. megastigma has improved in recent years but less is known of the endogenous control. This paper reports qualitative and quantitative measurements of carbohydrates and cytokinins during flower initiation and development of B. megastigma. A transient increase in zeatin riboside and dihydrozeatin riboside concentrations occurred in root and stem tissue within days of transferring the plants to cool (17/9ºC day/night) conditions. Starch concentrations increased throughout the plant within 2 days of transferring the plants to cool conditions and remained high for 10 weeks. A transient decrease in the starch concentration occurred during weeks 1-4 which correlated with early flower differentiation. Between weeks 10 and 12 in cool conditions, cytokinin concentrations increased, carbohydrate concentrations decreased, flower buds became committed to develop through to anthesis and a period of rapid bud expansion began. Evidence suggests that cytokinins may influence the rate of flower development by altering the mobilisation of carbohydrates.