Photosynthetic Activity in the Flower Buds of `Valencia' Orange (Citrus sinensis [L.] Osbeck)

Flower buds of ;Valencia' orange (Citrus sinensis [L.] Osbeck) were able to fix (14)CO(2) into a number of compounds in their own tissues under both light and dark conditions. The total incorporation, however, was about 4-fold higher in the light than in the dark. In the light, 50% of the total (14)C label was found in the neutral fraction (sugars), 22% in the basic fraction (amino acids), and 26% in the acid-1 fraction (organic acids). In the dark, about 95% of the (14)C label was incorporated into the basic and acid-1 fractions. Activities of ribulose bisphosphate carboxylase and phosphoenolpyruvate carboxylase (expressed in micromoles CO(2) per milligram protein per hour) averaged 1.95 and 8.87 for the flower buds, and 28.5 and 3.6 for the leaves, respectively. The ability of orange flower buds to fix ambient CO(2) into different compounds suggests that this CO(2) assimilation may have some regulatory role during the early reproductive stages in determining citrus fruit initiation and setting.