Dynamics of indole-3-acetic acid oxidase activity in suspension culture of sunflower crown-gall

IAA oxidase activity was determined in several growth phases of a suspension culture of sunflower crown-gall. During the short phase of intensive growth (zero passage - PO) a negative correlation was noted between enzymatic activity and the rate of growth. IAA oxidase activity increased to a certain level is not a factor limiting cell division. For protraction of the phase of intensive growth (first passage - P1), however, a decrease in the activity of this enzyme seems indispensable. IAA oxidase activity in the tested culture is under the control of inhibitors present in the cells and medium. High enzyme inhibition was observed in PO cells during the phase, of intensive growth and in P1 at the beginning and in the middle part of this phase. These results suggest' that the -auxin level determined in earlier studies in sunflower crown-gall culture is controlled by the IAA oxidase set. During the long phase of intensive growth (P1) this control is of negative feedback type