Comparative Photosynthesis in Developing Leaves of Brachystegia spiciformis Benth

Photosynthesis and dark respiration were studied during andafter the spring flush in Brachystegia spiciformis Benth. Variousparameters were examined including anthocyanin and chlorophyllcontent, Hill reaction activity, and gas exchange. Total chlorophyllcontent steadily increased reaching a constant value in fullyexpanded (25-d-old) leaves, whereas anthocyanin concentrationincreased as the chlorophylls but rapidly declined after 23d. Hill reaction measurements confirmed that leaf material fromevery stage of the flush (bud burst to mature leaves) was photosyntheticallyfunctional. The activity was low in flushing leaves with highanthocyanin content and then dramatically increased as leafanthocyanin content declined. Oxygen exchange measurements showedflushing leaves to have lower photosynthetic rates but higherrespiratory activity than mature leaves (60% and 120%, respectively).Gas exchange and in vitro electron transport were also generallycorrelated; Hill reaction activity was 128% of gas exchangein mature leaves and 92% in flushing leaves. It is concludedthat although photosynthetic rates are lower and respirationrates are higher in flushing leaves than in mature, fully expandedleaves, flushing leaves are fully photosynthetically competentand apparently require no net input of carbon for growth anddevelopment. Key words: Brachystegia, Hill reaction, photosynthesis, Zimbabwe