Abstract
Mitomycin C (MC), N-hydroxyurea (HU) and actinomycin D (AD) inhibit tumour formation on the primary leaves of Pinto beans. Agrobacterium tumefaciens was inoculated into bean leaves with application of the above named inhibitors at various times. It was found that MC action is strongest during inoculation and immediately after it, the maximal effect of HU take place within 12 h after inoculation, whereas the antitumour action of AD starts as late as 12 h after leaf inoculation. In view of the different degree of susceptibility of bacteria and plant cells to the inhibitors applied, the above described results allowed to distinguish three critical periods in the process of tumour formation in the tested host-pathogen system.