The application of treatments of physical and chemical nature in maize radiation mutagenesis --Ikhim, YG Radiation mutagenesis as one of the biotechnological directions of radiobiology has encountered a number of problems. The positive correlations between the dose and the radiation effect have been studied by many authors and are well-known. However, the dose increase leads to an enhanced possibility of lethal damages, and the mutation number in the radiated organism shows a loss of changes in genetic plasma. The problem of organism radiation responses, namely regeneration, repopulation and dedifferentiation, also arises at mutagenesis and in the course of studying the repair systems of multicellular plant organisms. Therefore, it is necessary to develop a method, with the aid of which it would be possible to overcome the above problems and keep the maximal possible number of mutagen modifications.

The postradiation (therapeutical) treatment is one of the most appropriate effects for the regulation of all the physiological processes, particularly, repair systems. The exogenic activation of intracellular processes modifies, to a great extent, the radiation damage, increasing the potential of the cell safety system with the help of somatical protection.

Table 1. Biometrical characteristics of plants.
 
Variances Plant height Leaf length Leaf width
MK-01
Control 97.93±1.88 56.77±0.78 5.74±0.06
Radiated control 72.84±2.31 51.27±0.85 5.09±0.09
g + Crossing 79.19±2.16* 52.54±0.77 5.01±0.09
g + Phytostim 74.77±1.96 51.39±0.81 4.85±0.09
g + EF 74.11±1.91 50.89±0.82 4.98±0.09
g + EHF 78.93±1.94* 51.60±068 5.03±0.08
19-3-3
Control 147.63±2.62 63.82±1.17 7.04±0.15
Radiated control 128.40±2.40 57.25±0.81 6.17±0.11
g + Crossing 137.29±2.31** 59.84±1.00* 6.23±0.12
g + Phytostim 118.83±4.52 51.37±1.53 5.66±0.17
g + EF 127.59±2.97 55.18±1.21 5.90±0.16
g + EHF 135.40±2.52* 59.42±1.09 6.18±0.12

The difference with the radiated control is significant: * - 5%, ** - 1%.

The studies carried out show a possibility of overcoming the problems of radiation mutagenesis in higher plants. The biometrical characteristics of the first generation plants express in their physiological condition the treatments studied (Table 1). The postradiation treatment with the synthetic growth regulator "Crossing" and exposure to electromagnetic field of an extremely high frequency (EHF) mitigated the damage effect and enhanced plant habitus in the two stocks under study, MK-01 and 19-3-3, while the radiation doses were within the lethal ones (250Gy). The biometrical indices of the plants exposed to postradiation treatment with the biostimulator "Phytostim" and the electric field (EF) of the current at an industrial frequency did not differ from the radiated control.

The findings of the cytological studies are summarized in Table 2. The number of aberrant cells in the control corresponds to the experimental data of other authors and does not exceed 1%, which proves a genetic stability and developed safety system of the 19-3-3 stock. The aberration number of the chromosome material upon radiation made 20.74%, which indicates serious damage of the genetic plasma. Among all the treatments studied, only one contributed to the activation of repair processes; i.e. the postradiation treatment with "Crossing" - 15.94%. However, the percentage of chromosome damage exceeds significantly the control in this treatment, which leads to the suggestion that a high percentage of morphogenetic modifications caused by the chromosome aberrations can be expected. The studies on the elimination of the damaging action of the postradiation treatment for the trait of the number of sterile pollen grains are given in Table 3. The samples of pollen grains were collected on four dates.

Table 2. The cytological studies on the action of postradiation treatments. (Ikhim, Scorpan, Lysikov, MNL 73, 1999.)

The exogenic factors applied after radiation induce the catalysis of repair reactions causing mistakes in the repair system action. The change in the physiological condition of the damaged plant organism must not lead to the elimination of the apical dominance, otherwise it will result in regeneration recovery or dedifferentiation of tissues. But in both cases, these lead to elimination of mutant population of the apex initials. The observation over M2 showed that this combined effect increased not only the number of specimens in the offspring, but the range and percentage of mutant forms.

Table 3. Sterility of pollen grains.
 
Variances I date, % II date, % III date, % IV date, %
Control 4.6 4.4 7.4 10.1
Radiated control 17.6 21.3 20.0 23.9
g + Crossing 12.8 14.7 19.9 22.8
g + Phytostim 15.4 18.3 21.8 27.6
g + EF 16.0 19.1 27.2 26.0
g + EHF 17.7 21.5 18.8 21.7

 

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