Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, including changes in amount per unit area of anthocyanin and chlorophyll, in leaves of seedling mango (Mangifera indica L. cv. Irwin) trees were determined to understand what controls the rate of photosynthesis (Pn) at various stages of development. The young leaves of seedling trees contained high concentrations of anthocyanin. During enlargement of leaves, the disappearance of anthocyanin and the accumulation of chlorophyll occurred concomitantly; the anthocyanin content began to decrease markedly once the leaf area had reached a maximum. During the early period of leaf development, the thickness of mesophyll tissue decreased temporarily, but when the length of the leaf reached half that of a mature leaf, the mesophyll began to thicken again. Small starch grains appeared in the chloroplasts of the young leaves and chloroplast nucleoids (ct-nuclei) were distributed throughout the chloroplasts. When leaves matured, ct-nuclei were displaced to the periphery of chloroplasts because of the accumulation of large starch grains. Compared with young leaves, green and mature leaves contained greater concentrations of ribulose bisphosphate carboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemical examination of RuBisCO under the light microscope reflected the results of electrophoresis measurements of RuBisCO. Pn was low during the chocolate-coloured stage of early leaf development. In green and mature leaves Pn was higher; the average Pn was 7·6 mg CO2 dm-2 h-1 under light at intensities above 500 µmol m-2 s-1.Copyright 1995, 1999 Academic Press