Experimentally induced chromosome abberrations in plants. II. The effect of cyanide and other heavy metal complexing agents on the production of chromosome aberrations by x-rays

The effect of respiratory inhibitors and chelating agents on the frequencies of chromosomal aberrations produced by x-rays in Vicia

Nitrosophenylhydroxylamine-ammonium (cupferron), potassium cyanide, sodium azide, ethylenediaminetetraacetate (EDTA), α,α'-dipyridyl, and o-phenanthroline were tested (1) for their ability to enhance the frequencies of chromosomal aberrations produced by x-rays in the root tip cells of the broad bean, Vicia faba, and (2) for their ability to inhibit oxygen consumption of excised roots of the same plant. In all cases a close correlation was found between the inhibitory effect on respiration and the enhancement of the sensitivity to x-rays at low oxygen pressures. EDTA, dipyridyl, and o-phenanthroline did not affect respiration to any greater extent, and they were without influence on the radiosensitivity. Cyanide, azide, and cupferron, which strongly inhibited respiration, also increased the frequencies of chromosome aberrations produced by x-rays at low oxygen pressures. The relation between oxygen concentration and radiosensitivity was determined both in the presence and the absence of the respiratory inhibitor cupferron. When cupferron was present, the radiosensitivity was influenced by oxygen concentrations 30 times lower than those effective in the absence of the inhibitor. In an atmosphere of pure oxygen, an increase of radiosensitivity of about 20 per cent was obtained with cupferron, EDTA, and potassium cyanide.

The effect of extended anaerobic treatments on the chromosomes of Vicia faba

The effects of extended anaerobic treatments on Vicia faba lateral root-tip chromosomes were determined. It was observed that aberrations resulted from these treatments, and that the frequency varied from root to root as well as from experiment to experiment. It was suggested that the inconsistency observed might be due to variation in the abilities of different roots to produce energy via fermentation routes. If this were true, an inhibition of fermentation would result in a more consistent aberration frequency. A fermentation inhibitor, NaF, was used in combination with extended anaerobic treatments. The observed frequency of aberrations after the combined treatments was generally higher and considerably less variable. Although other hypotheses might account for the NaF effect, the hypothesis most compatible with the evidence is that the effect is due to energy deprivation. The experimental results are discussed in terms of the aforementioned effect and in terms of three alternative hypotheses for the production of chromosomal aberrations as a consequence of a lack of energy. It is concluded that damage might result from a build-up of normal cellular compounds to abnormally high concentrations which would act directly or indirectly on the chromosomes, from the breakdown of DNA as an energy source, or simply as a result of the fact that the chromosome needs energy to remain intact.

Participation of a non-respiratory ferrous complex during mitosis in roots

A systematic survey was undertaken, of the effects of carbon monoxide and hydrogen cyanide (in the presence of 20 per cent oxygen), in darkness and light, on the relative rates of respiration, mitosis, and interphase in pea root tips. The inhibition of respiration by carbon monoxide was light-sensitive, but the inhibition by hydrogen cyanide was light-stable. The inhibitions were presumably due to combination of the inhibitor with the iron of cytochrome oxidase, in its divalent and trivalent forms respectively. In contrast, the inhibitions of mitosis by both poisons proved to be light-sensitive. The light-sensitive inhibition of mitosis by carbon monoxide shows that an iron complex is responsible for the process. That the inhibition of mitosis by hydrogen cyanide is also light-reversible shows that, in contrast with cytochrome oxidase, the mitotic iron complex remains always in the divalent state. The relative affinities of the mitotic ferrous complex, in molar units, were 0.68 for CO/O₂, and 0.37 for HCN/O₂. The properties of the complex are analogous to, yet distinct from, Gastrophilus haemoglobin and reduced cytochrome oxidase. It is considered that the arrest of mitosis by oxygen lack, carbon monoxide, and hydrogen cyanide is definitely due to interference with this unidentified, non-respiratory ferrous complex.

Experimentally induced chromosome aberrations in plants. I. The production of chromosome aberrations by cyanide and other heavy metal complexing agents

The finding of Lilly and Thoday that potassium cyanide produces structural chromosome changes in root tips of Vicia faba was confirmed. Like mustards, diepoxides, and maleic hydrazide, potassium cyanide seems to act on cells at early interphase. A tendency of cyanide breaks to be concentrated in heterochromatic segments of the chromosomes was evident. The production of chromosome aberrations by cyanide proved to be practically unaffected by the temperature during treatment. In agreement with Lilly and Thoday, the effect of potassium cyanide was found to be dependent on oxygen tension during treatment. The effect of potassium cyanide increases with increasing oxygen concentration up to 100 per cent oxygen. In the absence of oxygen, potassium cyanide was not completely inactive, but produced a low, though significant frequency of aberrations. Pretreatments with 2.4-dinitrophenol did not influence the effect of potassium cyanide. When bean roots were treated with potassium cyanide before a treatment with 8-ethoxycaffeine, or at the same time as they were treated with 8-ethoxycaffeine, the effect of 8-ethoxycaffeine was almost completely suppressed. The effects of a number of other heavy metal complexing agents were also tested. Sodium fluoride, potassium thiocyanate, carbon monoxide, o-phenanthroline, 2.2-bipyridine, and sodium azide were without radiomimetic effect under the conditions employed, and so was a mixture of sodium azide and sodium fluoride. A low, but quite significant, radiomimetic effect was obtained after treatments with sodium diethyldithiocarbamate, cupferron, and 8-hydroxyquinoline. Under anaerobic conditions, the effects of cyanide and cupferron were both quantitatively and qualitatively indistinguishable. Unlike the effect of cyanide, the effect of cupferron was not enhanced by the presence of oxygen. The effects of the same heavy metal complexing agents were tested on the activities of the enzymes catalase and peroxidase. The activities of both of these enzymes were found to be totally inhibited only by potassium cyanide. In the other cases, little correlation was found between ability to inhibit the activities of these enzymes and ability to produce chromosome aberrations. In a number of experiments, hydrogen peroxide was found to be without radiomimetic effect, whether alone or in combination with potassium cyanide. t-Butyl hydroperoxide proved to be active. The effect of t-butyl hydroperoxide was substantially increased by pretreatments with 2.4.-dinitrophenol. The results are discussed, and it is concluded that the observations made do not support the hypothesis that hydrogen peroxide is involved in the production of chromosome aberrations by potassium cyanide. The possibility that organic peroxides are involved cannot be excluded on the bases of the experimental results. As an alternative hypothesis, it is suggested that iron or other heavy metals are present in the chromosomes and that cyanide and other heavy metal complexing agents produce chromosome aberrations by reacting with these metals.