EFFECT OF NITROGEN APPLICATION AND SINK MANIPULATION ON THE CONTENTS OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE, PHOSPHOENOLPYRUVATE CARBOXYLASE, AND CHLOROPHYLL IN LEAVES OF MAIZE DURING THE MATURATION STAGE

By sink (ear) manipulation and additional nitrogen application at the flowering stage, studies were carried out to determine the changes in the contents of nitrogen and photosynthetic components; ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC), and chlorophyll. Then the relationships between the amount of these photosynthetic components and dry matter production were analyzed in maize plant (Zea mays L.) as follows. 1) Additional nitrogen application did not affect the dry matter accumulation, nitrogen absorption, and the decrease of the content of leaf nitrogen. Although additional nitrogen application did not affect the amounts of nitrogen, Rubisco and chlorophyll in leaves, the amount of PEPC decreased clearly in leaves mainly above the ear leaf. Thus it was found to be difficult under canopy conditions to retain photosynthetic components and to increase dry matter production by additional nitrogen application. 2) By sink manipulation, dry matter accumulation and nitrogen absorption decreased, but nitrogen absorption recovered with additional nitrogen application. By sink manipulation, the amounts of nitrogen and chlorophyll increased in all the leaves, while the amount of Rubisco increased in those above the ear leaf, and the amount of PEPC in the leaves at higher positions (e.g. 18th leaf). By sink manipulation, since the amount of photosynthetic components in leaves increased, it was regulated by the sink demand for nitrogen. However, by sink manipulation, since the dry matter production decreased, the activity of the photosynthetic components was not always related to the construction (and/or depression of degradation) of photosynthetic components.