Experimentally Induced Chromosome Aberrations in Plants

Abstract

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.

Production of Two Different Types of Chromosome Breaks by X-Rays

“…Since it was suggested by Mazia (1954) that the ionic bonds involving divalent cations such as Mg++ and Ca++ play an important role in maintaining chromosome organization, many workers have reported the results supporting the hypothesis (Steffensen 1955(Steffensen , 1957Kihlman 1957 ;Kaufmann and McDonald 1957 ;McDonald and Kaufmann 1957 ;Matsuura and Takehisa 1962). The ionic bonds to maintain the integrity of chromosome structure have also been suggested by the experiments with inorganic metal salt treatments (Kaufmann and McDonald 1956 ;.…”

Iron: Its Intracellular Localization and Possible Role in Cell Division

“…To determine the effects of the microincineration procedure on various ionic constituents of the cell, replicate suspension cultures containing 100 ml of cells at 2 X 105 cells/ml were labeled to equilibrium with either 45Ca (10 ,4Ci/ml), 5"Fe (5 MCi/ml), "5Zn (10 MCi/ml), 6"Ni (1 MACi/ml), or "4Mn (1 ,uCi/ml). Twenty-ml aliquots were centrifuged for the estimation of cell volume (or mass) (Bellco Glass, Vineland, N.J.).…”

“…They were then either dried directly or submerged in 0.1 N HCl for 30 min before rinsing and drying. The preparations were then placed in a Temco muffle furnace (Type 1500) at room temperature, gradually brought up to 540'C over a period of 6 hr, maintained at that temperature for at least 4 hr, and gradually cooled over a 4 to 6-hr period. The slides were immediately examined under phase contrast, in some cases after treatment with 0.1 N HCl as described under Results.…”

On the Radiomimetic Effects of Cupferron and Potassium Cyanide

“…According to Lilly and Thoday (9) the chromosomal aberrations observed after treatments with KCN may actually have been produced by hydrogen peroxide, which is believed to accumulate in the cell as a result of the inhibitory action of cyanide on cytochrome oxidase and on peroxidedestroying enzymes. The reasons why this hypothesis is hardly tenable have been discussed in a previous paper (3). The possibility that organic peroxides are involved could not be rejected (3), and since this hypothesis would account for the influence of oxygen, it is still regarded as a possible explanation for the radiomimetic effects of KCN and cupferron.…”

“…In addition to their ability to enhance x-ray sensitivity, the two best studied of these inhibitors, cupferron and potassium cyanide (KCN), have radiomimetic effects; i.e., they are able to produce structural chromosome changes in the absence of radiation (9,8,3). Studies on the radiomimetic effects of KCN (3) have shown that the effect is strongest 24 to 36 hours after the treatment, which indicates that KCN does not produce chromosome aberrations in cells which are in the second half of the mitotic cycle during the treatment.…”