RESUMEN
Cysteine (an aminothiol) is known to protect against radiation damage, and is understood to do so by generating hydrogen peroxide which subsequently inhibits RNA synthesis. Our results showed inability of catalase to remove or reduce the magnitude of radioprotection by caffeine and/or cysteine at optimal/suboptimal temperatures in barley. This observation was adequately corroborated by data on frequency of chromosomal aberration, peroxidase activity and total protein content. On the contrary, catalase tended to enhance the radioprotective effectiveness of cysteine. Macromolecular synthetic patterns in caffeine and/or cysteine treated embryos were too inconsistent to permit a logical conclusion with regard to their positive involvement in the biochemical pathway of chemical modification of radiation damage. On the other hand, mutually annihilatory reaction hypothesis based on physico-chemical principles provides a satisfactory explanation for the observed effects.