Change in content of ribulose 1, 5-bisphosphate carboxylase during development and senescence of mulberry (moms alba l) leaves

Abstract

The formation and loss of ribulose 1, 5-bisphosphate carboxylase (RuBPCase) was followed during two distinct phases of mulberry growth, i.e. from flushing to full development of leaves in spring and from the onset of the autumnal senescence to the falling of the leaves. The level of RuBPCase protein in the leaves of the field-grown mulberry trees was determined by rocket immunoelectrophoresis. The level of RuBPCase protein increased along with leaf development in spring, and the increase was more rapid in the leaves which opened later. In the leaves that opened in early June, the level of RuBPCase protein was maximum within one month after the leaves opened. At that time, the ratio of RuBPCase N to total N in these leaves reached 0.43. In the leaves which had completed their development, a gradual increase in the level of RuBPCase protein lasted for a while, and then the RuBPCase protein was mobilized during leaf senescence as a result of the sequential emergence and development of new leaves. Specific RuBPCase activity (per mg of RuBPCase protein) increased during leaf expansion and decreased after full expansion. After the termination of the new growth in early October, the RuBPCase protein content remained steady for a certain period of time. Then, in early November, it began to decrease, but its decline was so gradual even for the older leaves in lower shoot positions that the fallen leaves still retained more than half of the RuBPCase protein level observed at the onset of autumnal leaf senescence. Specific RuBPCase activity declined toward late autumn. Thus the characteristic redistribution of RuBPCase nitrogen within a plant was observed during two distinct phases in the life cycle of mulberry leaves. © Taylor & Francis Group, LLC.