Effects of O2-concentration, dose-rate, LET and cysteamine on the radiation-induced changes in viscosity of the cytoplasm in the statocytes of barley roots.

Abstract

SummaryChanges in viscosity can be used to measure changes in the structure of cytoplasm. This was studied in vivo by measuring the velocity of sedimentation of statoliths in root-cap cells of barley. The effects of oxygen-concentration (∼21 per cent to ∼1·4 × 10−3 per cent), dose-rate (600 to 2·1 × 1011 rads min−1), LET (x-rays, 10 MeV electrons and 14 MeV neutrons), and the competition between oxygen and cysteamine for organic radicals were investigated. The activation energy for the viscous flow of cytoplasm decreased after irradiation from 7·5 kcal mole−1 to 4·8 kcal mole−1, indicating structural changes. The results support the hypothesis that the increase in viscosity of cytoplasm is due to increased hydrogen-bonding between macromolecular structures, resulting from reactions of organic radicals with oxygen, and that the decrease in viscosity is caused by the fragmentation of macromolecular components.