Anatomical development and biochemical alterations in ribulose bisphosphate carboxylase-oxygenase accumulation during leaf enlargement in Amaranthus tricolor

Anatomical features and biochemical changes in ribulose bisphosphate. carbo xylase-oxygenase (RuBisCO) accumulation were observed to identify the facto rs that control photosynthetic activity related to leaf enlargement in Amar anthus tricolor plants. In the upper portion of the leaves, chlorophyll con tent increased rapidly during the early stages of leaf expansion; the antho cyanin content in the basal green/red portion of the leaves continued to in crease during their enlargement. The lamina taken before unfolding consiste d of a six-layered plate, which included the abaxial and adaxial epidermise s and 4 layers of mesophyll parenchyma. Leaf thickness and palisade cell le ngth approached a maximum when leaf areas reached 20 cm(2) (about 100 mm in leaf length). The ratio of leaf mesophyll cells to bundle sheath cells dec reased rapidly as leaf areas increased. Small starch grains accumulated wit hin the chloroplasts of mesophyll cells, while they gradually accumulated w ithin bundle sheath cells. Immediately after unfolding, many fully differen tiated stomata appeared simultaneously. Mature leaves contained higher conc entrations of RuBisCO protein than did immature leaves. Before leaf unfoldi ng, RuBisCO protein is localized within the chloroplasts of mesophyll cells . Following differentiation of the bundle sheath, RuBisCO is mainly localiz ed within the chloroplasts of bundle sheath cells. There is little obvious anatomical development of mesophyll tissue between the. green portions and the green/red portions of the leaves in A. tricolor.