Ontogenetic changes in the contents of ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase, and chlorophyll in individual leaves of maize

Abstract

Contents of nitrogen, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC) and chlorophyll in individual leaves of maize were measured during growth, and the following results were obtained.

1.	According to the changes in the nitrogen content, each leaf was subdivided into 3 classes: class I, 2nd to 6th leaf emerged at the early vegetative stage, class II, 8th to 12th leaf emerged during the reproductive growth stage, and class III, 14th to 18th leaf emerged during the booting stage. During the vegetative growth stage, class I leaves played an important role in nitrogen retranslocation as well as carbon assimilation because the ratio of the amounts of Rubisco-N, PEPC-N, and chlorophyll to the amount of nitrogen decreased rapidly after reaching a maximum value, indicating that photosynthetic components were decomposed preferentially for nitrogen retranslocation. During the maturation stage, class II leaves contributed mainly to the supply of nitrogen to ears because the ratio of the amounts of Rubisco-N, PEPC-N, and chlorophyll to the amount of nitrogen decreased, and class III leaves contributed to the assimilation of carbon because the nitrogen content and the ratio of the amounts of Rubisco-N, PEPC-N, and chlorophyll to the amount of nitrogen remained high during the maturation stage.
2.	Changes in the content of nitrogen of individual leaves during growth were not related to the changes of the Rubisco, PEPC, and chlorophyll contents. Therefore, the content of the photosynthetic components did not always depend on the status of nitrogen nutrition in a leaf.
3.	After the maximum amounts of nitrogen, Rubiseo, PEPC, and chlorophyll were obtained, at first the amount of Rubisco decreased rapidly, followed by that of PEPC, while the maximum amounts of nitrogen and chlorophyll decreased more slowly. This means that Rubisco may thus be the most important source for nitrogen retranslocation.

Key Words:

• chlorophyll
• leaf senescence
• nitrogen nutrition
• phosphoenolpyruvate carboxylase
• ribulose-1,5-bisphosphate carboxylase/oxygenase