Regulation of Tubulin Degradation in Isolated Zinnia Mesophyll Cells in Culture

Abstract

Tubulin degradation in isolated Zinnia mesophyll cells in culture was investigated by pulse-chase labeling with [35S]-methionine and two-dimensional electrophoresis. Tubulin degradation changes dynamically during culture. Almost no tubulin degradation occurs in the cells on the first day in culture. Treatment of these cells with colchicine activates the degradation of tubulin, but not of proteins other than tubulin. In the presence of colchicine, the α and β-subunits of tubulin are degraded together and the half life of each subunit is approximately 6 h. After 2 d in culture, there is active degradation of tubulin even in the absence of colchicine. Colchicine did not inhibit new synthesis of tubulin in Zinnia cells. This is very different from the results reported in cultured mammalian cells, whereby unpolymerized tubulin elevated by colchicine-treatment depresses its own synthesis. These and previous results dealing with changes in the level and synthesis of tubulin in cultured Zinnia cells (Fukuda 1987), are discussed in relation to the regulation of tubulin metabolism in cultured Zinnia cells.