THE EFFECT OF AUXIN STARVATION ON THE GROWTH OF AUXIN-DEPENDENT TOBACCO CELL-CULTURE - DYNAMICS OF AUXIN-BINDING ACTIVITY AND ENDOGENOUS FREE IAA CONTENT

The growth of a cell strain derived from the stem pith of tobacco (Nicotiana tabacum L., cv. Virginia Bright Italia) was investigated in subcultures grown at various levels of synthetic auxins. Both partial and complete auxin starvation resulted in a decrease of the frequency of cell division. For these treatments the endogenous free indole-3-acetic acid content increased substantially at the commencement of the exponential growth phase. The possibility that the receptivity of the cells to auxin changed during the growth cycle was examined by measuring the activity of a membrane-bound auxin-binding site. In subcultures grown in a medium with an optimal auxin concentration the maximum auxin-binding activity was restricted to the end of the exponential growth phase. In the cells cultivated in partially or completely auxin-deprived media the auxin-binding activity increased to varying extents. These results probably reflect mechanisms controlling both the intracellular content of free auxin and the sensitivity of the cells to exogenous auxin supply (including auxin binding) with respect to the cell division and/or growth.