Comparative photosynthesis in developing leaves of Brachystegia spiciformis Benth
Tuohy, J.; Choinski, J.J.
Journal of experimental botany 41(229): 919-923
ISSN/ISBN: 0022-0957 DOI: 10.1093/jxb/41.8.919
Photosynthesis and dark respiration were studied during and after the spring flush in Brachystegia spiciformis Benth. Various parameters were examined including anthocyanin and chlorophyll content, Hill reaction activity, and gas exchange. Total chlorophyll content steadily increased reaching a constant value in fully expanded (25-d-old) leaves, whereas anthocyanin concentration increased as the chlorophylls but rapidly declined after 23 d. Hill reaction measurements confirmed that leaf material from every stage of the flush (bud burst to mature leaves) was photosynthetically functional. The activity was low in flushing leaves with high anthocyanin content and then dramatically increased as leaf anthocyanin content declined. Oxygen exchange measurements showed flushing leaves to have lower photosynthetic rates but higher respiratory activity than mature leaves (60% and 120%, respectively). Gas exchange and in vitro electron transport were also generally correlated; Hill reaction activity was 128% of gas exchange in mature leaves and 92% in flushing leaves. It is concluded that although photosynthetic rates are lower and respiration rates are higher in flushing leaves than in mature, fully expanded leaves, flushing leaves are fully photosynthetically competent and apparently require no net input of carbon for growth and development.