Further aspects of the radioprotective mechanism of thiourea.

Thiourea in three different concentrations ranging from 10-4-M to 10-2-M was employed in pre- and post-treatments to test whether it decreases the chromosomal fragment frequency induced by 1000 R of X-rays in the growing root tips of Hordeum vulgare. In pre-treatment experiments thiourea in 10-2-M concentration yielded the maximal protection of 28.9 percent against radiation- induced chromosomal fragments. In post-treatment approximately a similar rate of protection is secured. It is discussed that the test-chemical protected the chromosomes against X-rays by two different mechanisms. The recovery process by restitution of the broken chromosomal fragments and the protection against initial radiation damage were the possible protective mechanisms displayed by thiourea in this plant material.