Changes in auxin activity in tumourous and normal tobacco calluses treated with morphactin IT 3233

The addition of morphactin IT 3233 in 1-40 mg/dm3 concentrations to the medium inhibited the growth in vitro of normal and tumourous tobacco calluses. The auxin activity (estimated by the Avena coleoptile straight growth test) of the acid ether extracts from these tissues increased. The activity of zone I (Rf 0.2-0.4, 0.5, solvent system: butanol:water:ammonia 10:10:1) in normal tissues increased more intensively than that of zone II (Rf 0.6-0.8, 0.9). In tumourous tissues, however, these changes were smaller and they concerned merely zone I of auxin activity (Rf 0.0-0.5). It seems that the mechanism of morphactin activity in both kinds of tissue is different. It may be supposed that the excessive accumulation of auxins induces growth inhibition of tissues. A previously found increase in the activity of IAA-oxidase influenced by morphactin might be considered as an adaptation to a higher level of IAA