Magnetic Centers (Free Radicals) Produced in Cereal Embryos by Ionizing Radiation

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Abstract
Barley seeds, barley embryos, and wheat embryos (ground wheat germ) were irradiated with X- and gamma-rays and examined for the presence of magnetic centers (assumed to be radicals) by electron paramagnetic spin resonance methods. Radicals could be detected after[image]10-kr exposures. Decay was more rapid in the presence of moisture and greater in the presence of oxygen. About 2 to 3 times as many radicals are detected after irradiation of dry wheat germ (1.5% water content) as are detected after irradiation of wet germ (8.5%). About 1011 radicals/ m of dry weight of wheat germ, irradiated dry in air, are found after an exposure of 1 kr of Co60 gamma-rays. The radical signal from irradiated wheat germ was broad, with a half-width about 27 gauss and was similar to signals from irradiated protein. For equal weights and doses, a water-soluble protein fraction of wheat germ gave about 3 times as large a signal as whole germ, alcohol-soluble protein and residue fractions were about the same, and a carbohydrate fraction about 1.3 times as large; a fat and oils fraction gave no detectable signal. Signals from barley embryos and from the wheat fractions were indistinguishable from those of whole wheat germ; the carbohydrate fraction alone was but slightly different. Some remarkable similarities are seen between the effect of various environmental and storage conditions on the decay of radicals and the aftereffects in seeds.

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