Changes in the content of poplar isoplastocyanins a and b during vegetation cycle

Abstract

Changes in the content of isoplastocyanins a (PCa) and b (PCb) in Populus nigra leaves were studied during complete vegetation cycle (from April 30 to October 28). Measurements were made every 7 days. The procedure included extraction and purification of total protein followed by analytical isoelectric focusing and densitometry of obtained isophoregrams. The positions of PCa and PCb were determined by comparison with the positions of the highly purified two isoforms. The PCb/PCa ratio was calculated from the areas of the corresponding densitometric peaks. The amount of PCb was one half of PCa amount in the earliest stage of the leaf formation as well as during the longer part of the summer, e.g., the second half of July, August, and September. During the most active period of the poplar growth, e.g., June and the first half of July, the ratio was about or above unity. This result could be important for understanding the specific functional significance of PCa and PCb.