PROTECTIVE PROPERTIES OF CYSTEINE, SODIUM HYPOSULFITE, AND SODIUM CYANIDE AGAINST RADIATION INDUCED CHROMOSOME ABERRATIONS

Abstract

Cuttings of Tradescantia paludosa were rooted in tap water with continual aeration, then transferred to lucite vessels. After 24 hrs. in Hoagland and Snyder''s nutrient soln. they were transferred to fresh nutrient solns. containing various concns. of cysteine, sodium hyposulfite or sodium cyanide. After 1 hr. the plants in the soln. of chemical compd. were exposed to continuous gamma radiation from a Co60 source for 48 hrs., with a total dose of 50 r. Meristematic root-tip cells were scored at anaphase for acentric fragments and bridges, but the effects of the chemicals were based on the fragment data, since the bridges occurred in too low a frequency. Two different experiments were run using cysteine-HCL at low pH. In both cases more protection was given to the chromosomes than in tests using cysteine in a partly neutralized medium. The greatest effect of neutralized cysteine was a 35% reduction in fragment freq. at 10-2 [image] concn., whereas the max. effect of cysteine at lower pH was a 60% reduction at 3 x 10-4 [image] concn. When plotted on a semilogarithmic scale the relationship between concn. of cysteine and % protection was almost linear for neutralized cysteine, with a suggestion of linearity for cysteine atlow pH. For sodium hyposulfite (Na2S2O4) a low concn. of 10-5[image] gave 12.8 fragments per 100 cells compared to 23.4 in the control. No further decrease was obtained with a higher concn., the max. protection being a 46% reduction in fragment freq. Sodium cyanide (NaCN) at concns. of 10-4 [image] and 5 x 10-4 [image] gave relatively little protection, but at 10-3[image] a reduction in fragment frequency of 25% was obtained. The possible mechanisms involved in the protective action of the chemicals are discussed. The difference in protective ability between cysteine at low pH and neutralized cysteine was thought to be due to easy decomposition of cysteine to cystine in a neutral-ized medium. Sodium hyposulfite, as a strong reducing agent, was thought to act by removing oxygen from the tissue, thus preventing the formation of certain reactants during irradia-tion. The protective action of sodium cyanide may be more complex, involving metabolic changes.