Modulation of soluble auxin-binding proteins in soybean cell suspensions

Rapidly growing cell suspensions of soybean were analyzed for the presence of cytoplasmic high-affinity binding sites for auxin. Cytosol preparations were studied in lag, log and early stationary phase of the growth cycle. Two binding sites were detected, which show some similarities with binding sites previously reported from etiolated pea epicotyls. While the number of both sites declined in the cytoplasm during the growth cycle, the number of one of the two sites increased at the onset of rapid cell divisions. In parallel, both sites exhibited an increase in binding affinity during the growth cycle. The data will be discussed in relation to other reports on soluble auxin binding as well as to possible physiological functions.