Electron paramagnetic resonance (EPR) studies were conducted on barley seeds exposed to normal (H₂O) and deuterated (D₂O) moisture, irradiated with 750 Gy at 77 K. Reported here, for the first time, are the trapped electrons formed on γ-irradiation of seeds at 77 K. Electrons are stabilized/solvated with an increase in the moisture content (H₂O/D₂O) of seeds. The recombination of the trapped electron with radical cation gave intense thermoluminescence emission at 110 K. With the increase in temperature and the destruction of singlet, unmasking of an underlying heterogeneous population of free radicals was observed. These free radicals emanate mainly from the endosperm (∼95% by wt of the seed), whereas irradiated embryos show a broad multiplet of comparatively low amplitude. Radiolysis of carbohydrate, proteins (∼95% of endosperm), and lipids could possibly be responsible for the heterogeneous population of free radicals. Peroxyl radicals were also observed on annealing.

Keywords: Radiation effects; electron paramagnetic resonance; thermoluminescence; barley seeds; trapped electrons; organic peroxyl radical; endosperm; embryo