A Comparison of the Effects of X-Rays and Thermal Neutrons on Dormant Seeds of Barley

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Abstract
Dormant seeds of Himalaya barley subjected to 5000; 10,000, 15,000 and 20,000 r of X- radiation were compared with seeds exposed to thermal neutrons for 3, 6, 9, and 12 hours at a flux of 4.65 x 108 Nth/cm2/sec. Frequency distrs. and standard errors were detd. for seedling heights at 14 days. Seeds subjected to the 3 highest doses of X-rays gave a wide range in height distrs.; the range increased with dosage. These differences were significantly different from the control. With thermal neutrons the range in height distrs. was as narrow for all treatments as for the control. Differential delayed killing characterized the material subjected to the 3 highest doses of X-radiation. Similar lethality patterns did not occur in the thermal neutron-treated material. After 40 days, essentially all seedlings in the 12-hour treatment had ceased growing, whereas all seedlings in the 9-hour treatment were actively growing. 6 hours in the thermal column caused a slightly higher chromatinic bridge frequency in root tip cells than had previously been obtained with a lethal dose of X-rays. However, seedling injury from this treatment was not excessive. The 9- and 12-hour treatments gave an aberration frequency 1.5 and 2 times as great, respectively, as has been obtained with a lethal dose of X-rays. For similar frequencies of chromosomal aberrations, there was less injury in seeds subjected to thermal neutrons than in those treated with X-rays. This indicates that X-rays may have proportionately more effect on extra-chromosomal elements of the cell than thermal neutrons.