[en] The question of mutual action of sVnchrotron radiation (SR) and living objects and the influence of powerful radiations on the peculiarities of their functioning is a major problem in all fields where SR in applied, as well as in medicobiological aspects of space flights. The present report summarizes new experimental findings concerning the action of magnetic-inhibiting radiation on Nicotiana tabacum - roots in oxygen and helium atmosphere. Comparative studies have been carried out on ''oxygen effect'' of SR and X-ray radiation by traditional radiobiological equipment. The experiments have been performed on the 2 synchrotron channel of Yerevan Physical Institute Electron Accelerator. The circular current of the accelerator equals 1 ma at a maximal energy of electrons in the ring 4.5 GeV. Nonmonochromatized SR coming out from the beryllium window of the current conductor entered a special maylar chamber which was filled with oxygen and helium. 4-day old roots of tobacco seeds were radiated in the chamber. The radiation dose in X-ray, as well as in SR equals 500 rad/min. X-ray radiation was carried out with the use of a RUP-200/20 equipment at a regime of J=15 ma, E=183 kV. In applying 500, 00 and 2500 rad in oxygen atmosphere a marked maximum of chromosome aberration frequency was noted at 2500 rad. Comparative investigations have shown that in radiating the roots by X-ray in oxygen atmosphere, the percentage of chromosome aberrations constitutes 4.5 at 2500 rad, while in SR it equals 24. The ''oxygen effect'' has been demonstrated, and the protective effect in helium atmosphere. The question of dosimetry is discussed, and basing on modern views a working hypothesis is presented which explains the marked damaging effect of SR action in oxygen atmosphere