Cytogenetic Effects of Radiation on Agricultural Plants Observed in the
Chernobyl region during the First Years after the Accident
Stanislav A. GERASKIN, Vladimir G. DIKAREV, Yevgenia Ya. ZYABLITSKAYA,
Alla A. OUDALOVA, Yevgeniy V. SPIRIN
Russian Institute of Agricultural Radiology and Agroecology,
249020, Obninsk, Kaluga Region, Russia: riar@obninsk.org

Abstract
The cytogenetic consequences of radioactive contamination by the fallout after the accident at
the Chernobyl NPP in 1986 to agricultural crops have been studied. In the acute period after theaccident (1986), when the absorbed dose was mostly provided with external β- and γ-radiation, theradiation injury of agricultural crops resembled the effect produced by acute γ-radiation atcomparable doses as basic cytogenetic tests testify. The yield of cytogenetic damage in leaf meristemof plants grown in the 10-km zone of the ChNPP in 1987-1989 (the period of chronic, lower level
radiation exposure) was shown to be enhanced and dependent on the level of radioactive
contamination. The rate of decline with time in cytogenetic damage induced by chronic exposure
lagged considerably behind that of the radiation exposure. Analysis of genetic variability in three
sequential generations of rye and wheat revealed increased cytogenetic damage in plants exposed tochronic radiation during the 2nd and the 3rd years.

Introduction
The accident at the Chernobyl NPP in 1986 is unique in both the extent of radioactive contaminationand the values of the doses absorbed by living organisms. An estimation of total release of fission products(without noble gases) amounted to 1.85⋅1018 Bq [1]. The areas most heavily exposed to radiation were
natural and agricultural ecosystems within the 30-km ChNPP zone, with radioactive contamination
reaching several thousands of MBq m-2 in 1986. The Chernobyl accident happened in late April - early
May, i.e., the period of accelerated growth and formation of reproductive organs of plants, when theirradiosensitivity is high. The maximum impact to living organisms was caused during 10-20 days after theaccident when short-lived isotopes made a considerable contribution to the absorbed dose. During thesummer and early autumn of 1986 the dose rate on the soil surface dropped to 20-25% of the initial value[2]. Since the autumn of 1986, the radiological situation in the exclusion zone has been stabilised; theacute irradiation at relatively high dose rates was replaced with low dose rate chronic exposure thatpersists up to the present time.
Cytogenetic and biological effects have been studied in rye seeds collected from agricultural fields inthe 30-km ChNPP zone in 1986, and on intercalary leaf meristem of winter and spring crops grown on
experimental plots in the 10-km ChNPP zone in 1987-1989.
Description of experimental plots
Seeds of winter rye of the “Belta” cultivar (from 50-100 main ears per plot) were collected on 4-6
August, 1986 from 5 m2 plots in five fields with different dose rates of γ-radiation in the 30-km ChNPP
zone. Seeds from a granary were used as control. The radiological characteristics of the experimental plotsat the time of seed sampling are presented in Table 1.
The experimental plots in 1987-1989 were chosen with regard to the level of radioactive
contamination of the territory, landscape and economic use of the land prior to the accident. Two pairs of287

Table 1. Radiological characteristics of farm fields in the 30-km zone of the ChNPP.
Plotσ, (MBq.m-2)
Dγ, (Gy)Dβ, (Gy)
1. Kozhushki
19.6
0.18
1.15
2. Chamkov
58.1
0.33
2.80
3. Radin
61.1
0.58
3.40
4. Borzhshevka
129.5
1.20
6.50
5. Krasno
263.8
1.15
10.80
σ - total contamination density within 0-2 cm soil layer in August, 1986;
Dγ, Dβ, Dβ+γ - doses absorbed over the vegetative period by plant critical organs.

Dβ+γ, (Gy)
1.33
3.13
3.98
7.70
11.95

Table 2. Radionuclide composition and contamination density on experimental plots in the 10-km
zone of the ChNPP (May 15, 1988).
Plot
1
2

Radionuclide composition, (%)

Location

Type of soil

Contamination
density,(MBq.m-2)

90

Meadow behind
Chistogalovka
Meadow before
Chistogalovka

soddy
podzolic

11.7

11.2

15.3

4.3

18.1

51.1

sandy loam

106.0

8.1

13.7

5.3

25.0

47.9

65.8

2.8

20.0

4.6

20.4

52.2

454.0

9.1

13.1

4.6

20.7

52.5

3

ABZ

4

Red forest

peaty humus
gley
peaty humus
gley

Sr

106

Ru

134

Cs

137

Cs

144

Ce

plots were chosen to obtain comparative results. The plots in each pair were similar in soil type, but had
diverse levels of radioactive contamination (Table 2). All four plots are situated 5-10 km west of the
ChNPP along the Yanov-Chistogalovka road. The soils are typical for the Ukrainian Polesie, i.e. soddy
podzolic, sandy and sandy loam, with different degrees of cultivation, a low availability of mineral
nutrition and low sorption capacity for the most radionuclides. The arable layer has a low content oforganic matter, available phosphorus and potassium, and a relatively high content of readily hydrolysable
nitrogen. The soil solution reaction is acid (pH=4.4 - 4.6) and sub-acid (pH=5.1 - 5.3). A detailed
description of plots was given in [3]. Winter (rye and wheat) and spring (barley and oats) crops were
sowed using appropriate agricultural practices. The area of the experimental plots varied from 5 to 25 m2.
Samples of the leaf intercalary meristem of spring barley and oats were collected when the rudimentaryears reached 5 cm above the ground (at 2-3 weeks after sowing). Samples of winter rye and wheat were
picked 2 times per year, at 3-4 weeks after sowing in the autumn and on the 10th day after thecommencement of growth in spring
Materials and methods
Experiment in 1986
Seeds of winter rye collected in 1986 were allowed to germinate at 25-26° C. 15-30 seedlings were
fixed at 16, 18, 20, 22, 24, 40, 48 and 72 hours of growth. Temporary squash slides prepared from the root
apical meristem of each seedling were stained with aceto-orcein. In each slide, the mitotic index was
calculated per 1000 cells, all ana-telophase cells were scored for aberrations; the aberration spectrum
consisted of chromatid (single) and chromosome (double) bridges and fragments, as well as lagging
chromosomes. 20-40 seedlings were simultaneously measured to determine the main root length. The
laboratory germination rate was studied using the accelerated method of Stepanov [4].
To estimate the total density of radioactive contamination and the doses absorbed by the plants, soil
was sampled by “envelop” method (taking samples from four corners and from the centre of the plot andcalculating the density as an average) on each of the five fields. The samples were analysed by γ288

spectrometry of the upper layer (0-2 cm) samples.
The estimation of the total dose for rye over the vegetative period in 1986 was based on theradionuclide composition of the fallout and models describing both the growth of cereal plants and theradionuclide migration in the soil profile. The absorbed dose of γ-radiation was calculated by summing up
the contributions from all lines of the spectrum obtained by γ-spectrometry on May 8, 1986 at assumptionof a uniform radionuclide distribution in the soil to a depth of 1 cm. In calculations of the absorbed dosefrom β-radiation, the total β-radioactivity was assumed to consist of two parts. The first one is distributed
over the soil surface and decreases from 100 % to 0 during the whole vegetative period (100 days) and thesecond one is distributed uniformly within the surface 1 cm soil layer and increases from 0 to 100 %. The
absorbed doses of β-radiation were calculated by integrating the point source dose attenuation function foreach radionuclide as described by [5]. The absorption coefficient for tissues covering the critical organ
was set equal to 0.5.
Experiments in 1987-1989
Samples of the leaf intercalary meristem collected from the crop plants in 1987-1989 were fixed inacetic alcohol (1:3), stained with aceto-orcein and examined for aberrations (bridges and fragments) in
ana-telophase. Five replicates were made for each plot at every sampling. Then, 100 ana-telophases werescored for each replicate.
An estimate of doses absorbed by the leaf meristem of plants in 1987-1989 was based on the data on
soil radioactivity level and composition of the radionuclide contamination. Models of the infinite uniform
source and of the infinite 20-cm thick layer source were used to calculate doses from β- and γ-radiation,
respectively. The duration of the radiation exposure before sampling leaf meristem in spring crops was
taken to be 30 days; in winter crops - 35 days for the autumn sampling and 210 days for sampling in thespring of the next year. When doses absorbed by a growing point over the whole vegetative period were
estimated, the time between appearance of the growth point above the soil surface and harvesting was
assumed to be equal to 100 days. γ-Radiation made the main contribution to absorbed dose during thistime.
The radiometric analysis showed that the contamination density of soil varied considerably even
within the area of one plot although the relative contents of radionuclides in all samples were similar(Table 2). Therefore, an average value for the density of radioactive contamination was calculated fromthe data on the absorbed dose rate in air. The ratio between the contamination density of soil and theabsorbed dose rate in air was determined experimentally at the plot, which had the least variability in themeasured levels of radioactive contamination. The dose rate of γ-radiation in air was measured withlithium fluoride thermoluminiscent dosimeters (TLD-100). Prior to measurements, the dosimeters were
calibrated in a γ-radiation field of 137Cs against the reference dosimeter 27012. To record γ-radiation only,
the detectors were exposed in a 3 mm thick protective aluminium capsule. Changes in the dose rate of γrays with time were registered by DRG-01T dosimeter.
Optimum sample sizes needed for the estimation of examined values with a certain relative probableerror at a given confidence level were determined by a method of statistical analysis of empirical
distribution [6]. Student’s test and confidence intervals were used to confirm statistical significance.
Results and Discussion
Winter rye, 1986
The experimental plots differed in the radioactive contamination of the soil surface layer and the doseabsorbed by plant critical organs over the vegetative period by almost an order of magnitude (Table 1).
According to the classification of zones of chronic radiation exposure of natural populations [7], the289Table 3. Aberrant cells in seedlings root meristems of winter rye seeds collected in the 30 km
ChNPP zone (mean ± SE).
Plot Dose, (Gy)

Cells in ana-telophase

Aberrant cells

Control
952
40
1
1.3
749
33
2
3.1
1402
101
3
4.0
787
51
4
7.7
447
49
5
12.0
668
95
Significance of variation from control: * - p<5%, ** - p<1%, *** p<0.1%;

Aberrant cell frequency,(%)
4.20 ± 0.65
4.41 ± 0.75
7.20 ± 0.69*
6.48 ± 0.88
10.96 ± 1.48**
14.22 ± 1.35***

Table 4. Damage distribution and severity of damage to aberrant cells in winter rye.
Number of cells with the
Severity of damage,MD,
following quantity ofPlot
AC ACc(aberrations per damaged(%)
aberrations
cell)
1
2
3 4
5
Control 40
4
27
5
4 0 0
32.5
1.36 ± 0.11
1
1.3
33
3
29
1
0 0 0
12.1
1.03 ± 0.10
2
3.1
101
9
64
23
3 1 1
36.6
1.39 ± 0.07
3
4.0
51
5
31
11
2 1 1
39.2
1.48 ± 0.19
4
7.7
49
5
29
9
4 2 0
40.8
1.52 ± 0.13
5
12.0
95
11
43
30
5 4
2
54.7
1.71 ± 0.12
Cells with complex indistinguishable damage were excluded from calculation of severity of damage.
AC - total number of aberrant cells; ACc - number of cells with complex damage; MD is a percent of cellswith multiple and complex damages.
Dose,
(Gy)

radiation-induced biological effects should dominate over those of other ecological factors at least on thetwo experimental plots with the highest levels of radioactive contamination. The contribution of βradiation to the total absorbed dose is different for each plot, but in all cases it is 6-9 times higher than thatof γ-radiation.
Table 3 presents the results of the cytogenetic analysis of seedlings root meristems of winter ryeseeds collected on contaminated plots. Even a dose of 3.1 Gy absorbed by plants results in a significant
increase in the yield of aberrant cells. It is pertinent to note that significant increase in the aberrant cells
rate in the root meristem of other agricultural crops was observed after exposure of seeds to γ-rays atcomparable doses [8, 9].
Data on the damage distribution per cell are given in Table 4. To calculate the severity of damage in
the aberrant cells, we used information on biological variability of this value among seedlings. The
analysis of changes in the severity versus the absorbed dose showed a significant growth in the degree ofcell damage along with radiation exposure. Overall, the severity of damage at chronic irradiation is within
the limits registered in our previous experiments on exposure of seeds of agricultural crops to γ-rays atcomparable doses [8,9].
Analysis of data on specific types of structural aberrations and their partial frequency (Table 5) has
shown that there are no essential changes in the aberration spectrum with dose. The prevalent types ofcytogenetic disturbance in the variety of rye examined, both for control and at chronic irradiation, arechromatid mutations followed by lagging chromosomes and chromosome aberrations. The low relative
contribution of chromosome aberrations is supposed to be a specific feature of the biological material
used. In our previous investigations [8,9] of structural mutations induction in root meristems of wheat andbarley seeds exposed to ionising radiation, the contribution of chromosome aberrations was also small.
290

Table 5. Structural mutations spectrum in winter rye exposed to radioactive contamination.
Different type aberrations
m’
f’’
m’’
g
f’
m’
f’’
m’’
Number%control
49
5
27
13
1
3
10.2
55.1
26.5
2.0
6.1
1
1.3
31
4
18
9
0
0
12.9
58.1
29.0
0
0
2
3.1
128 9
63
41
5
10
7.1
49.2
32.0
3.9
7.8
3
4.0
68 13
32
18
0
5
19.1
47.0
26.5
0
7.4
4
7.7
67
7
34
23
0
3
10.4
50.8
34.3
0
4.5
5
12.0
144 19
59
55
4
7
13.2
41.0
38.2
2.8
4.9
Cells with complex indistinguishable damage are excluded.
TA - total number of aberrations; g - lagging chromosomes (genome mutations); f’, m’ - chromatid (single)
fragments and bridges with associated fragments; f'”, m” - chromosome (double) fragments and bridges
with associated fragments.
Plot

Dose,
(Gy)

TA

g

f’

Table 6. Some viability indicators of seeds collected in the 30 km ChNPP zone (mean ± SE).
Mitotic index, (%)
Main root length, (mm)GerminaDose,Plottion,(%)(Gy)
16-24 h40-48 h72 h16-24 h40-48 h72 h-Control

1.69 ± 0.25

3.83 ± 0.26

3.09 ± 0.17

1.96 ± 0.19 22.95 ± 1.19 34.21 ± 3.42

62.0 ± 2.4

1

1.3

1.16 ± 0.23

2.64 ± 0.23*

3.24 ± 0.79

2.22 ± 0.20 12.85 ± 1.13 34.46 ± 2.17

87.5 ± 1.7*

2

3.1

1.73 ± 0.22

2.29 ± 0.17*

3.95 ± 0.35

2.27 ± 0.17 17.75 ± 0.97 37.97 ± 2.93

74.5 ± 2.2*

3

4.0

1.25 ± 0.18

2.54 ± 0.18*

3.79 ± 0.26

1.83 ± 0.14 13.35 ± 0.93 45.29 ± 3.33

88.8 ± 1.6*

4

7.7

0.83 ± 0.17

2.75 ± 0.16*

3.99 ± 0.25

1.64 ± 0.11 12.70 ± 0.77 36.06 ± 3.21

70.8 ± 2.3

5

12.0

1.11 ± 0.20

2.61 ± 0.27*

2.98 ± 0.32

1.93 ± 0.24 13.80 ± 0.73 25.48 ± 3.49

31.2 ± 2.3*

Mean values over the first (16-24 h) and the second (40-48 h) mitosis are presented.
Significance: * - p<5%.
Such an unusual result may be due to the possible induction at G1 stage, of long-lived potential damage
that is later realised as genuine mutations at S and G2 stages. Dubinin & Nemtsova [10] have obtained
similar results analysing aberration spectrum in root meristems of irradiated seeds of agricultural plants.
Table 6 presents data on some viability indicators of seeds collected on the plots in the 30 km ChNPP
zone. The mitotic indices determined at 8 time points (16-72 hours after germination) show that there is an
insignificant tendency for mitotic activity to decline with the increase in the dose absorbed. A significant
radiation depression of mitotic activity was observed only in 40-48-hours seedlings. However, at this time
point, the mitotic indices don’t correlate with dose. Seed germinating power shows statistically significant
stimulation effects at doses of 1.3-4.0 Gy, and considerable, statistically significant inhibition at the doseof 12 Gy. Attention should be paid to the fact that some of the morphological indices illustrating theviability of germs at early stages of ontogenesis depend on dose. It should also be noted thatmorphological stimulation (Table 6) was accompanied by high and significant increment of cytogenetic
disturbances. This result appears a good illustration of the ambiguous nature of “stimulation” and indicatesthat the term should not be considered as a synonym for “benefit” or even harmlessness of exposure,because this outcome, assumed to be positive in terms of economic efficacy, may simply be a small part ofa wider biological phenomenon that is negative overall.
Thus, in the first acute period after the Chernobyl accident, when the absorbed dose was primarily
formed by external β- and γ-radiation, the radiation injury to agricultural crops, according to the basic
cytogenetic tests, resembled the effect produced by acute γ-irradiation at comparable doses.

291

Table 7. Aberrant cell frequency in the leaf meristem of spring crops grown on experimental
plots in the 10-km ChNPP zone.
Barley
Oats
Dose,
Plot
(cGy)
Number of AC Frequency of AC, (%) Number of AC Frequency of AC, (%)
1
2.05
142
203
28.4 ± 2.0
40.6 ± 2.2
3
12.09
181
161
36.2 ± 2.1
32.2 ± 2.1
2
17.90
156
274
31.2 ± 2.2
54.8 ± 2.2∗
4
78.46
261
271
52.2 ± 2.2∗
54.2 ± 2.2∗
AC is aberrant cells. Significance of variation from plot 1: * - p<5%.
Spring barley and oats, 1988
Experiments with spring crops (barley and oats) were only carried out in 1988. Table 7 gives the dataon the frequency of aberrant cells in the leaf meristem of barley and oats grown on plots with a nearly 40fold difference in radioactive contamination density. The yield of aberrant cells trends to rise with theabsorbed dose, indicating the radiation-induced nature of the observed changes. The levels ofcytogenetical damage in oats generally exceed those in barley at the same absorbed doses, which is thereverse of the relationship for values of LD50 reported by [11].
In this study there are unexpectedly high levels of cytogenetic disturbances in comparison with ourprevious experiments on acute [12,13] and chronic γ-irradiation of barley plants [14]. According to [1214], the spontaneous level of aberrant cells in the leaf meristem of barley was 10-14%. In the present
study, the yield of cytogenetic disturbances was 2-3 times higher than the spontaneous occurrence
expected from our works on acute γ-irradiation of barley plants even at plots with the lowest levels ofradioactive contamination. Such an apparent discrepancy between the level of genetic effects expectedfrom the dosimetric data and the level observed in the experiment has also been reported by other authors
who had carried out investigations in the 30-km Chernobyl zone [15,16].
Winter wheat and rye, 1987-1989
An estimation of consequences of radioactive contamination should take into consideration that wintercrops are subjected to radiation for a longer time and their leaf meristem lies within the upper, mostdensely contaminated soil layer during the winter dormancy period. Experiments with winter crops (wheat
and rye) were carried out from the autumn of 1987 till the autumn of 1989. Therefore, from the data
available, conclusions can be drawn not only about dose dependence of cytogenetic damage rate but also
about how the plant response to radiation changed as the absorbed dose decreased with time due to both
radioactive decay and the migration of radionuclides in soil.
Frequencies of aberrant cells in the leaf meristem of winter rye and wheat grown on plots with diverselevels of radioactive contamination are given in Table 8. For winter wheat, there is a significant decreasein the yield of cytogenetic disturbances with time from the accident at all plots except plot 3. For winterrye, such a decrease is observed at plots 2 and 4. At the same time, the yields of the aberrant cells per dose
unit rise with time in all autumn samplings (Table 8). This means that the rate of decline in the cytogenetic
damage to plants lags behind that of radiation exposure. This phenomenon was also reported by [17].
The regression analysis for each year and for each sampling time has shown a general significant
development in the frequency of aberrant cells with increase in the dose absorbed by plants, indicating
thereby the role of radiation exposure in the observed alterations. However, no significant dose
dependence was revealed: a) in the autumn of 1989, in rye (p<0.07), when the absorbed dose decreased by
2.6 times compared with 1987 and b) in the spring of 1988, in wheat (p<0.22) and rye (p<0.06), whendoses absorbed by plants were maximal over the investigated period and one could expect an apparent
dose-effect relationship. If we distinguish two sets of the data for peaty humus gley (plots 3 and 4) and forsoddy podzolic sandy loam (plots 1 and 2) soils, there is the expected dose dependence, as seen in the case292

Table 8. Aberrant cells frequency in leaf meristem cells of winter crops grown in the 10-km
ChNPP zone.
Rye
Wheat
Sampling time
Dose, (cGy)AC, %AC per 1 cGyAC, %AC per 1 cGy
Plot 1 (soddy podzolic soil)
Autumn 1987
3.88
19.0 ± 1.8
4.90 ± 0.97
32.4 ± 2.1
8.35 ± 1.24
aAutumn 1988
1.99
21.4 ± 1.8
10.75 ± 1.39
23.0 ± 1.9
11.56 ± 1.43
Autumn 1989
1.03
17.48 ± 1.70
20.2 ± 1.8
19.61 ± 1.78
18.0 ± 1.7 a
Spring 1988
17.94
26.0 ± 2.0
1.45 ± 0.53
53.2 ± 2.2
2.97 ± 0.76
Spring 1989
10.26
20.4 ± 1.8
1.99 ± 0.62
23.2 ± 1.9 b
2.26 ± 0.66
Plot 3 (peaty humus gley soil)
Autumn 1987
23.15
1.04 ± 0.45
20.2 ± 1.8
0.87 ± 0.42
24.0 ± 1.9
Autumn 1988
11.67
25.4 ± 1.9
2.18 ± 0.65
24.8 ± 1.9
2.13 ± 0.64
Autumn 1989
5.81
23.4 ± 1.9
4.03 ± 0.88a
21.2 ± 1.8
3.65 ± 0.84a
Spring 1988
106.5032.8 ± 2.1
0.31 ± 0.25
34.6 ± 2.1
0.32 ± 0.25
Spring 1989
59.74
0.37 ± 0.27
24.0 ± 1.9 b
0.40 ± 0.28
22.0 ± 1.9 b
Plot 2 (sandy loam soil)
Autumn 1987
33.50
32.4 ± 2.1
0.97 ± 0.44
33.4 ± 2.1
1.00 ± 0.44aAutumn 1988
17.48
24.2 ± 1.9
1.38 ± 0.52
25.6 ± 2.0
1.46 ± 0.54
Autumn 1989
9.36
2.20 ± 0.66
20.6 ± 1.8 a
2.20 ± 0.66
20.6 ± 1.8 a
Spring 1988
155.7559.6 ± 2.2
0.38 ± 0.28
68.6 ± 2.1
0.44 ± 0.30
Spring 1989
90.63
24.6 ± 1.9 b
0.27 ± 0.23
24.6 ± 1.9 b
0.27 ± 0.23
Plot 4 (peaty humus gley soil)
Autumn 1987
148.780.30 ± 0.25
39.6 ± 2.2
0.27 ± 0.23
45.2 ± 2.2aaAutumn 1988
76.14
26.6 ± 2.0
0.35 ± 0.26
27.6 ± 2.0
0.36 ± 0.27
Autumn 1989
39.60
22.8 ± 1.9 a
0.58 ± 0.34
25.8 ± 2.0 a
0.65 ± 0.36
Spring 1988
687.2047.4 ± 2.2
0.07 ± 0.12
42.8 ± 2.2
0.06 ± 0.11
Spring 1989
392.490.08 ± 0.12
29.8 ± 2.0b
0.08 ± 0.12
29.8 ± 2.0 b
AC – frequency of aberrant cells;aand b – difference from the level of the autumn 1987 and the spring 1988, correspondingly, is significant,p<0.05.
of the spring crops. Attention is drawn to the abnormally low level of cytogenetic disturbances in wheat at
plot 3 in the autumn of 1987 and spring of 1988, which differ significantly from that at plot 1 with thelowest level of radioactive contamination. The reason for this abnormal observation is not clear yet.
It is interesting that slopes of fitted linear dose curves in autumn are considerably higher than in springof the following year for both cereals. So, the yield of aberrant cells in autumn has closer correlation withdose absorbed by plants than that in spring. Dose was accumulated over a prolonged time in spring
samples, so cytogenetic damage probably depends not as much on radiation as on other factors.
Variability in the plant generations
Over the entire period of investigations (autumn of 1987 - autumn of 1989), a part of the seeds
collected was planted again on the same plots, allowing study of genetic variability in three successive
generations of winter rye and wheat. The doses absorbed by a growing point of plant over the wholevegetative periods from planting to harvesting of 1987-1988 and 1988-1989 were in the range of 18 - 717
cGy and 11 - 418 cGy, respectively. Each of these doses accumulated during vegetation is a sum of twovalues, i.e. the dose absorbed from planting in autumn to the time of spring sampling (Table 8) and a doseabsorbed from spring sampling to seed harvesting. The last value is comparatively small because the mostpart of dose is delivered to plants with β-radiation while the growing point is under or near the soil surface
prior to the spring sampling.
In rye, in the autumn of 1989, at plots 2 and 4 with the highest level of radioactive contamination, the293frequencies of aberrant cells in the leaf meristem in plants growing on contaminated sites in the second
year (marked as the X2 generation) and the third year (the X3 generation) significantly exceed the values
for those growing only in the first year (the X1 generation) (Table 9).
In contrast to the results obtained by [18], the level of genetic variability in the X3 generation in thepresent study does not decline and even somewhat increases (Figure 1), though there is no statisticallysignificant difference between the yields of aberrant cells in the X2 and X3 generations. The results of ourstudy correspond well with the data reported by [15] who observed a rise in mutation load in the
Arabidopsis thaliana populations at all levels of radioactive contamination during the first 2-3 years after
the accident. In wheat, this tendency is more pronounced. In the autumn of 1989, a significant increase in
the frequencies of aberrant cells in the X2 and X3 generations, compared with X1, was recorded at 3 out of
4 plots (Table 9). Differences between the numbers of aberrant cells in the X2 and X3 generations are smalland statistically insignificant for both crops (Figure 1).
One of the possible explanations of the observed phenomenon is related to genome destabilisation inplants grown from seeds affected by radiation. Results from numerous experiments carried out withrepresentatives of different kingdoms of the living world [17,19] indicate that chronic irradiation inregions affected as a result of the accident at the Chernobyl NPP can cause heritable destabilisation ofgenetic structures that appears, in particular, as an increased yield of cytogenetic disturbances andkariotypic variability in the offspring of irradiated organisms. From these viewpoints, the phenomenon
observed in this study may be a reflection of the first stage in cytogenetic adaptation [20,21], that is,Table 9. Aberrant cells frequency in leaf meristem of winter rye and winter wheat in 3 subsequent plant generations grown on the plots in the 10-km ChNPP zone (sampling time is autumn 1989).
Rye
Wheat
D87-88,
D88-89,D,
Plot
Number of
Aberrant cell
Number of
Aberrant cell
(cGy)
(cGy)
(cGy)
aberrant cells frequency, (%) aberrant cells frequency, (%)
X1-generation (first year of planting on contaminated plots)
1
1.03
101
20.2 ± 1.8
9018.0 ± 1.7
3
5.81
117
23.4 ± 1.9
10621.2 ± 1.8
2
9.36
103
20.6 ± 1.8
10320.6 ± 1.8
4
39.60
114
22.8 ± 1.9
12925.8 ± 2.0
X2-generation (second year of planting on contaminated plots)
1
10.68
1.03
119
23.8 ± 1.9
13026.0 ± 2.0*
3
63.54
5.81
144
28.8 ± 2.0
13527.0 ± 2.0
2
95.93
9.36
155
31.0 ± 2.1*
146
29.2 ± 2.0*4
417.49 39.60
165
33.0 ± 2.1*
170
34.0 ± 2.1*
X3-generation (third year of planting on contaminated plots)
1
18.45
10.68
1.03
136
27.2 ± 2.0
13226.4 ± 2.0*
3
111.1
63.54
5.81
150
30.0 ± 2.0
15731.4 ± 2.1*
2162.05
95.93
9.36
179
35.8 ± 2.1*
150
30.0 ± 2.0*
4
717.2
417.49 39.60
163
32.6 ± 2.1*
167
33.4 ± 2.1
D – dose, accumulated from planting in autumn 1989 to the sampling time;
D87-88, D88-89 – doses, accumulated by parent plants during the whole vegetative period from planting up to
harvesting in 1987-1988 and 1988-1989 years, respectively
X1-generation – plants grown from intact seeds and accumulated dose D from planting in autumn 1989 to
the sampling time;
X2-generation – parent plants were sown in 1988, harvested in summer 1989 and planted again on the sameplots in autumn 1989. Genetical effects are the result of both the ancestral dose D88-89 and current exposure D;
X3-generation - parent plants grew on the same plots in 1987-1988 and in 1988-1989 and accumulated doses
D87-88 and D88-89, correspondingly. Seeds harvested in 1989 were sown again in autumn 1989 andplants of the X3 generation got dose D.
Significance of variation from the level of cytogenetic disturbances in the X1 generation: * - p<5%.
294

R YE

40
30

A b e rra n t ce lls, %

20
10
0
40

W HEA T30
20
X 1 g e n e ra tio n

10

X 2 g e n e ra tio n
X 3 g e n e ra tio n

0
0

10

20

30

40

D o se , cG y
Figure 1. Yield of aberrant cells in three successive generations of winter rye and wheat, grown on
contaminated plots.
chronic exposure to low-level radiation possibly alters the genetic structure of population. Response to an
external impact, such as an expansion of the gene pool variability providing a potential basis for thesubsequent selection of the most adaptable forms, is a reflection of the fundamental mechanisms(grounding the basis for life) [22] that ensure resistance of living systems and their possible adaptation tovarying conditions of the environment.
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