[en] The peroxidase and IAA-oxidase activities, the degree of auxin protection and the amount of soluble phenolics were determined in in vitro cultured shoots of a nonrooting mutant, inc, of tobacco compared to its wild homologue. The mutant and wild shoots showed similar peroxidase variations along the growth cycle of 21 days, but with higher levels of activity for the I ac mutant. During this growth cycle, the minimum of peroxidase activity occurred at day 14 for both tobacco whole shoots. However. this minimum of activity did not occur at the same day in the basal part of the stem, where roots may appear, of the two types of tobacco. Both mutant and wild whole shoots showed about the same IAA-oxidase activity in the fractions resulting from a gel filtration of the crude extracts through a sephadex G-100 column but differed in the degree of auxin protection. The rac shoots exhibited a very high level of auxin protectors of low molecular weight, among which chlorogenic acid. They were also characterized by eight to nine times higher level of soluble phenolics. The relationships between these biochemical aspects in relation to the absence of root formation in the me mutant are discussed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.