SOMATIC CROSSING OVER IN GLYCZNE M A X ( L . ) MERRILL : MUTAGENICITY OF SODIUM AZIDE AND LACK OF SYNERGISTIC EFFECT WITH CAFFEINE AND MITOMYCIN C *
Glycine max (soybean) is one angiosperm which lends itself to the study of somatic crossing aver. This is made possible because some varieties have gene combinatiorrs Y l l Y l l , Y, ,y l1 and y l l y l l in the segregating populations from Y,,y , , plants. The gene in question is responsible for chlorophyll synthesis. The Y I I Y , , plants have dark green leaves, Y l l y l l are light green and yl1ylI plants are golden yellow. The heterozygous plants have dark green, yellow and dark green-yellow (double) spots on the leaves of the untreated control material, whereas the two homozygotes are almost always devoid of somatic sectoring. Application of caffeine, or mitomycin C, to the seeds increased the frequency of double, dark green and yellow spots on the Y,,y , , background. Possibly, some dark green or yellow spots originate by failure of one of the two components of what might start as a double spot due to somatic crossing over. The application of NaN, increases the frequency of dark green or yellow spots, almost exclusively. The two spots increase in equal frequency. The y J l y l l plants so treated do not have any light green sectors, but dark green, Y,,Y,,, plants do develop a few light green or very dark green spots. The data indicate that NaN, is capable of inducing nondisjunction, but does not cause mutations (at this locus), chromosome fragmentations (segmental losses) or somatic crossing over to an appreciable degree. It has previously been shown that caffeine-induced chromosome rejoining in Vi& faba can be inhibited by treating the roots with NaN,. In the present experiments NaN, did not affect the processes of somatic crossing over as induced by caffeine or mitomycin C. The effect was additive. This system offers advantages for studying chemical mutagins in that somatic crossing over, point mutations, segmental losses through chromosome breakage and nondisjunction can all be studied in a single treatment to the seeds. ODIUM azide (NaN3) is an inhibitor of oxidative phosphorylation (LOOMIS and LIPMANN 1949). It has been shown to reduce ATP level in excised root tips of Vi& faba at concentrations around 10-4M, within one half hour (KIHLMAN et al. 1971b). This reduction in the level of ATP has been suggested to be responsible for a reduction in the frequency of 8-ethoxycaff eine-induced chromosome exchanges when NaN, is administered just before, or simultaneously with, Publication No. 504, from the Department of Biology, University of Nevada at Reno. The author is thankful for the help received from the Research Advisory Board of the University and for the renew of the manuscript by DR. R. A. NILAN. Genetics 7 5 : 265-277 Octoher. 1973.
EFFECT OF SODIUM AZIDE ON RADIATION DAMAGE AND PHOTOREACTIVATION
During investigations on the role of bacterial pigments in ultraviolet irradiation damage and in photoreactivation, several agents were tested as suppressors of pigmentation effects. Chromobacterium violaceum is extremely radiosensitive in that it shows very high inactivation by ultraviolet and also high photorecovery with white light. Sodium azide depresses both of these effects significantly. Previously, Wyss et al. (1948) demonstrated an increase in the mutation rate of Micrococcus pyogenes var. aureuw, grown in the presence of subinhibitory concentrations of this compound, and Clark et al. (1950) were able to stimulate recombination in Escherichia coli, strain K-12, under the same conditions. On the other hand, Bacq and Herve (1951) report a protective effect of azide and other respiratory poisons against X-ray damage in mice. A correlation of these effects with the known inhibitory action of azide on various iron-porphyrin enzymes appears evident, and an investigation of its applicability to other systems seemed to warrant testing on a broader basis.
Protection of mice against a lethal dose of x rays by cyanide, azide and malononitrile.
Cyanides (but not thiocyanate or cyanate) azide and malononitrile protect a significant percentage of mice irradiated by a single lethal whole body dose of X rays; these poisons are ineffective when given after irradiation. The protective effect of previously injected glutathione has been confirmed; the action of cyanide is increased by simultaneous administration of glutathione.