Inverse Correlation between Growth and Degrading Enzyme Activity of Seedlings after Gamma and Neutron Irradiation of Pea Seeds

Summary

The effect of gamma-, 14 MeV neutron- and fission neutron irradiation was investigated on the growth rate and degrading enzyme activities of pea seedlings. Both dormant pea seeds and 4-day-old growing seedlings were used for the experiments. Depending on the gamma dose between 15 and 300 Gy the height of pea seedlings was found shorter, and parallel with this the endogenous RNase and peroxidase activities were higher than in the unirradiated controls. Seedlings proved to be more sensitive by about one order of magnitude than seeds. Irradiation of seeds between 5 and 10 Gy slightly enhanced the growth rate of seedlings (10 per cent) and parallel with this, the RNase activity measured was lower than that in the controls.

On irradiation of seedlings with 14 MeV neutrons the growth inhibition and RNase activity enhancement was only 1·3 times more effective than in the case of irradiation of seeds. The following RBE values were obtained after irradiation of seeds, related to the biological effect of gamma rays: in growth inhibition, 6 for 14 MeV neutrons and 12 for fission neutrons, and the enhancement of two enzyme activities was 15–30 for 14 MeV neutrons and 45–58 for fission neutrons. In the case of seedling irradiation with 14 MeV neutrons the RBE was 1·0 for growth inhibition and between 3 and 6 for enhancement of enzyme activity. The isoenzyme pattern of RNase also changed: two isoenzymes became predominant after the gamma irradiation of seeds, characterized by molecular weights of 21,000 and 30,000, respectively. As a result of enhanced RNase activity, the degradation of longer polysomes to monomeric ribosomes occurred. Thus after ionizing irradiation of pea seeds and seedlings an inverse correlation was found between the growth rate of pea seedlings and the activities of degrading enzymes.