The influence of post-radiation treatments on genetic processes and mutation frequency --Ikhim, YG The series of post-radiation factors of a chemical and physical nature were used to study the variability of viability of M1 of maize. These factors were certain biological and synthetic regulators of growth, biologically active substances, electromagnetic irradiation of different frequency, etc. A significant increase was observed for the viability of mutants of the first regeneration under the influence of sublethal doses of irradiation for some variants. The frequency and spectrum of variability of genetic processes induced by g-irradiation for the same variants was maintained.

In the field experiments for the study of the variability of genetic processes on dependence of a post-radiation factors, the following methods were used. For the revealing of recessive lethal and vital mutations the process of induction of haploid forms was made. As a female form, line 19-3-3 was used and treated with the method mentioned above. As a male form haploid inductor, MHI was used. At the first step the variability of the induction was studied. By the marker system of the inductor, hybrid seeds were chosen with pigmentation of the aleurone and an embryo because haploid seeds have unpigmented embryos.

For determination of the frequency of mutations at a locus, a hybrid between the line MK-01 (female form) and the multimarker line 2-9M was used, marked with seven genes: ws3 (2-0), lg1 (2-11), gl2 (2-30), y1 (6-17), c1 (9-26), sh1 (9-29), wx (9-59). The staining of the aleurone of F1 seeds was estimated and the percentage of mosaic forms was counted.

Table 1 shows the variation of the genetic processes induced by the combined action. We have counted lethal mutations in the M2 by calculating the percentage of the plants grown from the number of the seeds sown. We agree that these findings are conditional as there are many factors causing the decreased plant emergence and death under the conditions of a field experiment. However, these figures are of a certain interest. A maximal number, 9%, of viable M2 genotypes was in the treatment Radiation+Crossing, while in the irradiated control the number of organisms carrying lethal damage was 100%. The second line shows the variation of the haploid induction in the 19-3-3 line using the MHI inducer. The findings suggest that this treatment technique may significantly modify the process of haploidy induction. Thus, the treatment Radiation+Phytostim and Radiation+SHF, influencing the plant physiology, changes significantly the percent of haploid seeds. This experiment was set with the aim of determining the number of recessive mutations capable of being displayed only at the haploid level of the organism organization. An experiment using a multimarker line 2-9M was set with the aim of estimating the mutation frequency per locus or 100,000 gametes which may change in relation to the treatment type. The line is marked for seven genes and particularly for the C1 locus (chromosome 9). MK-01 treated according to the techniques under study was used as a maternal form. A marker line was used as paternal form. While studying the F1 seeds, mosaicum was detected for the aleurone coloration. The high percentage of mosaics in the control suggests the presence of mobile elements in the genotype, but the exact kind of elements will be determined in the future. However, it is interesting to know to what extent this combined effect may influence the display of mosaicism. It is enough to compare the number of mosaics in the radiated control and Radiation+SHF treatment.

Table 1. Induction of variability of genetic processes by combined treatments.
 
  Control Radiated control g + Crossing g + Phytostim g + EF g + SHF
Lethal mutations in M2, % 0 100 91.19 98.45 94.90 95.73
Induction of haploidy in M2,% 5.38 5.37 5.32 6.58 5.92 4.19
Mosaic of aleurone coloration in F1,% 2.63 0.59 1.19 2.69 3.32 6.35

Table 2 shows the results of the investigation of the lethal recessive mutations and the mutations of the C1 locus of the MK-01 X 2-9M hybrid. The utilization of the haploid level allows the discovery of recessive mutations, particularly, lethal events. The percentage of surviving plants is expressed in relation to the number of seeds sown. The results show that the post-radiation treatments with the "Crossing" growth regulator do not reduce the number of mutations in comparison with the irradiated control, which has confirmed our cytological investigation (Ikhim, YG, MNL 74, 2000). This confirms that this growth regulator has an effect at the physiological level, without having a direct impact on genes. The post-irradiation treatment with SHF decreases significantly the level of lethal events. A similar pattern is observed in the research of the mutation number at the C1 locus. However, the frequency level has increased by 2-3 orders in all treatments.

Table 2. Mutation percentage at the utilization of combined treatments
 
Variants Lethal recessive C1
Control 86.59 0.0000
Radiated control 96.78 0.0658
g + Crossing 96.97 0.0988
g + Phytostim 100 0.0625
g + EF 95.24 0.0922
g + SHF 85.72 0.0453

The results presented show that it is reasonable to use post-irradiation treatments to modify viability of the first generation mutations and, notably, of the factors under study.
 
 

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