Download Genotoxicity of barley stripe mosaic virus in infected host plants

Cent. Eur. J. Biol.• 5(5) • 2010 • 633-640
DOI: 10.2478/s11535-010-0048-7
Central European Journal of Biology
Genotoxicity of barley stripe mosaic virus
in infected host plants
Research Article
Larisa I. Andronic*, Anatol G. Jacota, Valeriu V. Bujoreanu, Tatyana B. Grigorov
Institute of Genetics and Plant Physiology of the Academy of Sciences of Moldova,
MD 2002 Chisinau, Republic of Moldova
Received 26 January 2010; Accepted 09 April 2010
Abstract: A
comparative study of the effect of barley stripe mosaic virus (BSMV) and gamma irradiation on mitotic divisions in barley (Hordeum
vulgare L.) roots was performed by evaluating the mitotic index (MI), micronucleus (MN) frequency and sister chromatid exchanges
(SCE). Results indicate that, similarly to gamma irradiation at doses of 100, 150 and 250 Gy, BSMV reduces the mitotic activity,
increases the micronucleus frequency and the rate of SCE and promotes the formation of C-metaphases. In root meristematic cells
of the three barley cultivars studied (Galactic, Sonor and Unirea), the mitotic index of infected plants was found to be 52.5, 54.48 and
64.17%, respectively, lower than the uninfected control. An increase in frequency of sister chromatid exchanges was observed in all the
experimental variants. In treatments involving viral infection alone or in combination with gamma irradiation chromosomes with three
and more chromatid exchanges were observed, while their percentage in the control or in treatments with gamma irradiation alone was
reduced. The results of the study indicate that in plants derived from irradiated seeds, BSMV produces an effect that is correlated nonlinearly
with the radiation dose applied. Cytological analysis of mitotic divisions in barley roots revealed the genotoxicity of BSMV infection.
Keywords: B
arley stripe mosaic virus • Gamma radiation • Genotoxicity • Hordeum vulgare L. • Micronuclei • Mitotic index
• Mitotic division • Sister chromatid exchange
© Versita Sp. z o.o.
1. Introduction
In studying genotoxicity of various factors, a number
of parameters characterizing mitotic divisions are
used, such as mitotic index, micronucleus frequency,
and sister chromatid exchange (SCE) rate [1]. Mitotic
index may be used as a direct indicator of the genotype
response to various factors representing the organism’s
mechanism of adaptation at the cellular level ensuring
maintenance of homeostasis in cellular systems.
Mitotic index is an important criterion used in evaluating
proliferation processes [2]. Sister chromatid exchange
assay is considered to be one of the most sensitive tests
in assessing genotoxicity [3].
Evaluating features of the proliferation of vegetative
cells, including meristematic cells, involves analyzing
various plant responses to treatments [4]. Meristematic
cells respond rapidly and actively to endogenous
and exogenous factors [5]. The conservative nature
of proliferation processes allows various mitotic
633
division parameters to be used in monitoring studies.
Cytogenetic studies carried out by a number of authors
suggest that barley, a genetically well studied crop
plant, has successfully been used as a convenient and
sensitive test system [6]. Barley carries seven pairs of
chromosomes on which a large number of genes and
gene mutations have been localized and described.
Barley has been successfully used in genotoxicity
studies [1]. Barley is a host plant for barley stripe mosaic
virus (BSMV), a pathogen which has been shown
to produce genetic effects on the host plant, such as
induction of triploids and aneuploids in barley [7] and
wheat [8].
A number of studies have recognized the
contribution of viral infection to somatic and
meiotic recombination enhancement, resulting in
rearrangements which could be transmitted to
the next generation [9,10]. An increase in somatic
recombination is considered a general response of
plants to various factors, including pathogens [11].
* E-mail: [email protected]
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The increased genetic flexibility resulting from
recombination might facilitate adaptation of plant
populations to stressful environments.
Assessing proliferative processes of cells during
viral infection can contribute to the understanding of the
complex interaction between viruses and host plants.
The objective of the present study is the cytogenetical
evaluation of mitotic divisions in barley cells infected with
BSMV alone or in association with gamma irradiation.
2. Experimental Procedures
2.1 Biological material and exposure schedule
Three cultivars of spring barley (Hordeum vulgare L.,
2n=14), Galactic, Sonor and Unirea, were used in the
study. All seeds were initially tested for the presence of
virus infection by immunosorbent electron microscopy
(ISEM) [12]. Seeds confirmed to be non-infected were
used in further experiments. Barley seeds were exposed
to the following doses of gamma radiation: 100 Gy,
150 Gy and 250 Gy. RXM-γ-20 installation with Co60 as
source of radiation was used to produce gamma rays.
Barley plants from both irradiated seeds and untreated
seeds were mechanically inoculated with a barley stripe
mosaic virus (BSMV) extract. Plants derived from nonirradiated, healthy seeds that had been inoculated with
distilled water and presented negative results upon
virological examination served as the control. All three
investigated cultivars Galactic, Sonor and Unirea are
susceptible to BSMV and displayed external symptoms
at 10-14 days after mechanical inoculation.
2.2 Virological analysis
Control plants at the two- to three-leaf stage were mock
inoculated with distilled water. Leaves of the plants from
experimental lots, at the same stage, were infected
two times at two-day intervals with BSMV inoculum
using carborundum powder. Inoculum was prepared
by grinding leaf tissue in distilled water (1:2). Initially,
the extract was prepared from field-grown barley plants
that expressed symptoms specifically to those induced
by BSMV and presented positive response to ISEM
test using polyclonal anti-BSMV serum diluted 1:50
[12]. Further work involved material collected from
plants showing external disease symptoms and yielded
positive results through ISEM.
2.3 Cytological analysis
To study the induction of sister chromatid exchanges
(SCE) upon treatment with gamma irradiation alone
or in combination with BSMV infection, the frequency
of SCEs in mitotic chromosomes from root meristems
was analyzed using differential incorporation of
5-Brom-2’-deoxyuridin (BrdU). Seeds were germinated
in the dark until rootlets reached 2–3 cm in length. The
BrdU incorporation was performed during two cycles
of cell division by exposure to a mixture comprised of
100 µM BrdU, 0.1 µM 5-fluorodeoxyuridine (FdUrd) and
5 µM uridine (Urd). The procedure of material fixation,
maceration and staining was followed as previously
described [13].
For cytological analysis of mitotic index (MI) and
micronucleus (MN) test, rootlets that had reached
2–3 cm in length were subjected to direct fixation in
an acetic acid: alcohol (3:1) solution. The samples
were then rinsed in distilled water, mounted onto a
slide, macerated and stained with acetocarmine or
5% Giemsa (for micronucleus evaluation). MI was
expressed as the number of dividing cells per 100
scored cells and MN frequency was expressed as
the number of cells with MN per 1000 scored cells,
resulting from 10 separate seedlings for each group.
The criteria for the identification micronucleus were as
follow: (i) the MN had to be smaller than one-third of
the main nuclei; (ii) the MN could not touch the main
nuclei; (iii) the MN should have the same color and
staining intensity as the main nuclei.
2.4 Statistical analysis
The statistical processing of data was carried out using
the software package Statgraphics Plus for Windows
(version 2.1; Microsoft Corp., Redmond, WA, USA) and
Microsoft Excel. The contribution of variation sources
was computed following the ANOVA test results [14].
3. Results
3.1 Mitotic
index
and
micronucleus
frequency in barley root meristems under
viral infection and gamma radiation
According to the results of the cytological study, the
mitotic index (MI) in the genotypes under study was
10.44 in the cv. Galactic, 12.39 in cv. Sonor and 12.7 in
cv. Unirea. The mitotic index of seed material collected
from plants infected with BSMV and/or exposed to
gamma radiation was lower than the mean value of MI in
the control (Table 1). The largest decrease in the mitotic
index of cv.Galactic (69% lower than in the control)
occurred in the treatment where BSMV was used in
combination with gamma a radiation dose of 250 Gy.
A similar decrease in the MI was observed in treatments
of gamma radiation alone at a dose of 250 Gy. Exposure
to gamma radiation produced a dose-dependent effect.
The impact of gamma radiation at doses of 100 Gy and
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Genotoxicity of barley stripe mosaic virus in infected host plants
a)
b)
c)
Figure 1. Interphase
Interphases analyzed
Mitotic
Micronucleus
(number)
index value
frequency
Galactic
Control
Virus
100 Gy
100 Gy + virus
150 Gy
150 Gy + virus
250 Gy
250 Gy + virus
1683
1405
1800
1830
1890
1795
2405
2069
10.44±1.34
4.96±0.60***
5.65±0.58**
6.82±1.25*
5.60±0.89**
5.88±1.69*
4.27±0.71***
3.23±0.94***
0.233±0.037
0.633±0.059***
0.390±0.010***
0.363±0.025**
0.863±0.163***
0.983±0.194***
1.167±0.050***
1.223±0.133***
1.42
1.11
0.42
1.93
Sonor
meristematic cells in barley (Hordeum
vulgare L.) rootlets: (a) normal interphases in rootlets
of the control plants (x 850); (b) an interphase with a
micronucleus (indicated by an arrow) in rootlets of
barley plants, cv. Galactic, infected with barley stripe
mosaic virus (x 700); (c) a micronucleus (indicated by
an arrow) in meristematic cells of rootlets of barley cv.
Galactic irradiated with gamma rays at a dose of 150 Gy
and infected with barley stripe mosaic virus (x 1000).
Control
Virus
100 Gy
100 Gy + virus
150 Gy
150 Gy + virus
250 Gy
250 Gy + virus
2039
2737
2345
2263
2657
2340
2683
2014
12.39±0.93
5.64±1.04***
5.93±0.37***
6.33±0.43***
5.66±0.79***
5.90±1.55***
4.63±0.49***
4.59±0.66***
0.140±0.131
0.620±0.115**
0.477±0.124*
0.510±0.098**
0.687±0.154**
0.793±0.191**
0.933±0.146***
1.136±0.125***
0.37
0.43
0.99
Unirea
150 Gy was milder in the case of virus-infected plants
(the difference between treatments was statistically
significant at P≤0.05). The same pattern in mitotic index
modification was observed in the other two cultivars,
Sonor and Unirea. In the cv. Sonor, virus infection
caused a reduction in the frequency of mitotic cells
similar to that produced by gamma radiation at doses
of 100 Gy and 150 Gy. Upon irradiation of barley seeds
with gamma rays at a dose of 250 Gy, the mitotic index
value decreased 62%, practically to the same extent as
in the treatment using gamma irradiation at 250 Gy in
combination with virus infection (63%). In the case of cv.
Unirea, BSMV tended to enhance the mitodepressive
effect of gamma radiation at a dose of 150 Gy and to
reduce the effect of gamma rays at a dose of 250 Gy.
Reductions in the mitotic index in various treatments
(experimental variants) were accompanied by an increase
in the micronucleus frequency (Table 1, Figure 1).
In all three barley varieties studied, viral infection
alone induced a higher number of micronuclei than viral
infection in combination with gamma radiation at a dose
of 100 Gy. Treatment with gamma irradiation at a dose
of 150 Gy resulted in approximately the same frequency
of micronuclei as exposure to gamma radiation in
combination with viral infection. Gamma irradiation at
a dose of 250 Gy caused the frequency of micronuclei
to increase 5-fold over the control in Galactic, 6.7-fold
in Sonor and 4.3-fold in Unirea. The frequency of
Control
Virus
100 Gy
100 Gy + virus
150 Gy
150 Gy + virus
250 Gy
250 Gy + virus
1482
1661
1972
1895
1724
1966
2383
1980
12.70±0.79
4.55±0.51***
5.16±0.11***
5.51±0.76***
6.09±0.85***
4.91±0.25***
3.47±0.66***
5.06±0.53***
0.267±0.083
0.727±0.032***
0.356±0.006*
0.573±0.210*
0.700±0.069***
0.853±0.071***
1.143±0.222***
1.433±0.132***
0.60
0.42
1.52
Treatment
Table 1.
C-metaphase (‰)
Frequency of micronuclei in roots of barley plants derived from gamma-irradiated seeds and infected with barley stripe mosaic virus.
*; **; *** - significant difference from the control at P≤0.05; 0.01; 0.001
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L.I. Andronic et al.
micronuclei in virus-infected plants derived from seeds
irradiated with gamma rays at a dose of 250 Gy was
similar to that induced by gamma radiation alone.
Micronuclei are extranuclear chromatinic bodies
resulting from chromosome breaks or aneuploidy [1].
Examination of cytological preparations obtained
using the acetocarmine staining technique showed
micronuclei to be well-defined chromatinic structures
located in close proximity to nuclei and characterized
by wide variation in size. The presence of micronuclei is
considered to be an indicator of genome instability [15].
The occurrence of C-metaphases was observed in
barley plants infected with BSMV (Table 1, Figure 2).
In Galactic and Sonor, C-metaphases were visualized
in plants subjected to a combination of viral infection
and gamma radiation at doses of 150 and 250 Gy,
whereas in Unirea they only occurred in treatments with
simultaneous application of viral infection and gamma
radiation at a dose of 250 Gy.
Abnormalities of the C-mitosis type are believed
to be due to the division spindle restructuring [16].
C-mitoses may result in chromosome number doubling.
In the absence of cytokinesis, polyploid or bi- and polynucleate cells may form. In the case of phragmoplast
and cell wall formation, cells with different chromosome
numbers may arise [17]. The possibility of aneuploids
being induced by BSMV in wheat and barley has
a)
Figure 2. C-metaphase
b)
in rootlets of the barley cv. Unirea:
(a) infected with barley stripe mosaic virus; (b) irradiated
with gamma rays (150 Gy) and infected with barley stripe
mosaic virus (x 1200).
previously been described [7,8]. Cytological studies of
mitotic and meiotic divisions have shown BSMV particles
in direct association with microtubules [18], which may
explain the direct effect of the virus on components of
the spindle apparatus.
3.2 A study of sister chromatid exchanges
in barley (Hordeum vulgare L.) under
viral infection and gamma radiation
Analysis of sister chromatid exchanges (SCE) in three
spring barley cultivars (Sonor, Unirea and Galactic)
made it possible to determine the number of SCEs per
cell or chromosome in the case of infection with BSMV,
irradiation with gamma rays (at doses of 100, 150 and
250 Gy), as well as in the case of viral infection of plants
derived from gamma-irradiated seeds. The results of
the SCE test indicated that under normal conditions an
average of 5.6–6.1 SCEs per cell occur. Both gamma
radiation and viral infection increased the frequency of
SCEs (Table 2). In the case of viral infection, the highest
percentage of SCEs induced by BSMV was observed
in the cv. Unirea (a nearly 55.4% increase over the
control, at P≤0.001). The effect produced by gamma
radiation varied according to the dose applied to the
seeds as well as according to the genotype analyzed.
The frequency of SCEs in the case of exposure to
gamma radiation at a dose of 100 Gy increased by
40.1% and 33.2% over the control in barley Sonor and
Unirea, respectively, whereas the frequency of SCEs
in cv. Galactic only increased by 8.23% (P≤0.05). It is
only in the case of cv. Galactic that gamma radiation
at a dose of 150 Gy produced a more mitodepressive
effect (statistically confirmed) than gamma radiation at
a dose of 100 Gy. In the cv. Unirea, the rate of sister
chromatid exchanges per cell varied around 7.2 and
tended to decrease. When viral infection was combined
with gamma radiation treatment, the effect on the rate of
SCEs varied according to the genotype and the gamma
radiation dose applied.
Genotype analyzed
Treatment
Sonor
Unirea
Galactic
Control
6.128±0.337
5.561±0.259
6.108±0.265
Virus
8.359±0.299***
8.641±0.286***
8.703±0.312***
100 Gy
8.585±0.273***
7.410±0.284***
6.611±0.240*
100 Gy + virus
8.946±0.287***
7.973±0.314***
8.028±0.244***
150 Gy
8.846±0.295***
7.270±0.339***
7.973±0.269***
150 Gy + virus
8.385±0.281***
8.081±0.246***
9.054±0.274***
250 Gy
10.081±0.318***
9.540±0.358***
8.081±0.291***
250 Gy + virus
10.971±0.305***
8.811±0.321***
8.838±0.306***
Table 2.
The rate of sister chromatid exchanges (per cell) induced by BSMV in meristematic cells of roots of healthy and irradiated barley plants.
*; *** - the differences from the control are statistically significant at P ≤ 0.05; 0.001
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Genotoxicity of barley stripe mosaic virus in infected host plants
In plants of the cv. Sonor derived from seeds irradiated
with gamma rays at a dose of 100 Gy, BSMV infection
caused a larger increase in the SCE frequency. The rate
of SCEs induced by viral infection in Sonor irradiated
with gamma rays at a dose of 150 Gy was close to that
in the treatment where infection alone was applied. The
same tendency of reduction in SCE frequency was also
observed for the cv. Unirea with infection combined with
250 Gy treatment. In Galactic, BSMV infection caused
an increase in SCE rate compared to gamma irradiation
alone.
Analysis of SCEs in terms of distribution of exchanges
per chromosome revealed a tendency for dispersion to
increase in the case of experimental variants (P≤0.5)
(Figure 3). Examination of the spectrum of sister
chromatid exchanges indicated that the number and type
of SCEs are affected by both factors analyzed. While
in the control plants the rate of SCEs per chromosome
averaged 0.40–0.46, in some experimental variants
(treatments) it reached 0.69–0.73 (in Galactic and Sonor
irradiated with gamma rays at a dose of 250 Gy).
A study of SCE distribution has, in general, revealed
a tendency for the frequency of chromosomes with
three and more exchanges to increase, especially in
treatments using viral infection alone or in combination
with gamma radiation (Figures 3 and 4).
An increase in mean frequency of SCEs in the case of
viral infection, as well as in the case of gamma irradiation,
occurs predominantly due to multiple chromatid
exchanges whose percentage under normal conditions
is reduced (0.28–0.48 per cell). In experimental variants,
the percentage of multiple exchanges increased
substantially, reaching its maximum in the cv. Sonor
upon infection of BSMV in combination with irradiation by
gamma rays at a dose of 250 Gy. For this treatment, the
proportion of chromosomes with multiple exchanges was
found to increase 12.7-fold relative to that in the control.
Application of ANOVA revealed that barley stripe
mosaic virus, like gamma radiation, causes the frequency
of sister chromatid exchanges to increase. Analyses
Source of variance
indicate that effect on SCEs is dependent on the plant
genotype (3.6%), virus (6.1%) and radiation dose (13.4%)
(Table 3). In the aggregate, the degree of influence of
radiation against the background of viral infection may
increase or decrease, depending on the genotype and
the dose applied. The most powerful influence was found
to be exerted by gamma radiation as dependent on the
dose applied (13.4%).
a)
b)
c)
d)
Figure 3. M
etaphase
plates in meristematic cells of roots of
H. vulgare, cv. Unirea: (a) control, (b) barley stripe mosaic
virus, (c) gamma irradiation 150 Gy, (d) gamma irradiation
150 Gy + virus (x 1200).
a)
b)
c)
d)
e)
f)
g)
Figure 4. M
etaphase
chromosomes in Hordeum vulgare:
(a,b) chromosomes without chromatid exchanges,
(c) schematic representation of a metaphase
chromosome
without
chromatid
exchanges,
(d) a chromosome with a chromatid exchange in the
long arm, (e) a chromosome with a chromatid exchange
in each arm, (f) chromosomes with multiple chromatid
exchanges, (g) schematic representation of a metaphase
chromosome with a chromatid exchange.
Contribution of the source of
Degree of
Sum of
variance, %
freedom
squares
S2
F test
P
A: Virus
6.06
1
1.37672
1.37672
71.241
0.0000
B: Genotype
3.65
2
0.829628
0.4148129
21.47
0.0000
C: Radiation dose
13.42
3
3.04913
1.01638
52.50
0.0000
Interaction AB
0.3
2
0.0832031
0.0416016
2.38
0.0930
Interaction AC
3.95
3
0.898543
0.299514
17.15
0.0000
Interaction BC
3.01
6
0.684898
0.11415
6.53
0.0000
Interaction ABC
1.35
6
0.3059
0.0509834
2.92
0.0080
913
22.7279
Total
Table 3.
Analysis of variance of the SCE frequency in barley plants, healthy and infected with BSMV.
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Cytogenetic studies suggest that BSMV infection,
like gamma radiation, causes the number of SCEs to
change significantly. The effect of gamma rays on DNA
is well understood, and their ability to induce sister
chromatid exchanges in a dose-effect manner has
been described previously [19]. These findings have
been confirmed in our previous studies. The ability to
increase the frequency of SCEs in conditions of viral
pathogenesis is indicative of the genotoxic effect of the
pathogen involved. Genotoxic effects have also been
observed in infection by some animal viruses, such as
hepatitis B virus or hepatitis C virus [20]. BSMV appears
to have genotoxic effects, as evidenced by an increase
in sister chromatid exchanges, the rate of which, in most
cases, is dependent on multiple exchanges.
4. Discussion
Various factors, predominantly chemical agents, have
been shown to inhibit mitosis in crop plants, including
barley. A decrease in mitotic index has been reported in
barley plants exposed to sulfur dioxide [21], oxygenated
compounds [22], and some insecticides and fungicides
[17]. It is believed that variation in the mitotic index
values directly reflects the intensity of physiological and
biochemical reactions whereas the rhythm of variation
is dependent on the rate of enzymatic reactions [23].
A decrease in value of mitotic index with exposure to
various factors attests to the mitodepressive nature of
these factors, which inhibit cell divisions [24]. Hidalgo
and coworkers [25] explain the antimitotic effect of
herbicides (propham and chlorpropham) in Allium cepa
as inhibiting the activity of enzymes, including DNA
polymerase. A reduction in mitotic index may result
from inhibition of DNA synthesis in S phase of the cell
cycle [26] or cell blocking in the G1 period [27]. Inhibition
of mitosis may also result from retention of cells in G2
[16]. According to Yi et al. [21], a decline in proliferation
processes occurring in barley roots exposed to sulfur
dioxide may also be due to DNA degradation. The effect
of mitodepressive factors on mitoses is believed to be
stronger during S phase of the cell cycle [6].
Sister chromatid exchanges (SCEs) were first
described in plants by Kihlman and Kronborg [28]
by employing the Giemsa staining technique [29].
According to many reports, SCEs are brought about by
irreparable double-strand breaks occurring during DNA
replication, as has already been suggested by Wolff and
coworkers [30]. SCEs can also arise from disturbances
in the double-strand break repair process [31]. SCE
genesis is considered to be conditioned by DNA
replication events, in particular, those of replicative fork
formation during which sister chromatid recombination
may occur [32]. According to the replication model of
sister chromatid exchange proposed by Painter [33],
replication and repair of DNA double-strand breaks
occurring at the boundary of two replicon clusters
proceeding asynchronously. A similar situation may
result from changes in the rate of replication process
as well as from modifications in the structure of the
DNA molecule. A study of SCEs in Saccharomyces
cerevisiae revealed three mechanisms involved in the
generation of chromatid exchanges: induction of DNA
double-strand breaks, decline in the replication process,
and reduction of DNA-polymerase activation processes
[34]. In cells exposed to UV rays, X-rays, 4-nitroquinoline
1-oxide or methyl methanesulfonate, activation of genes
RAD55, RAD57 and RAD54 involved in repair of DNA
breaks has been observed. This phenomenon does not
occur spontaneously, contrary to the observation that
under normal conditions some chromatid exchanges
do occur. Results indicate that different mechanisms
are responsible for spontaneous and induced SCE
generation. Although the mechanism of SCE generation
is still unclear [35], it is well established that SCE
genesis is associated with DNA lesions.
According to many reports, plant viruses are
capable of inducing various genetic effects [36-40],
including modification of the sister chromatid exchange
rate [36,41]. SCE analyses have demonstrated the
mutagenic effect of the bean common mosaic virus in
bean plants that varies according to the stage of viral
pathogenesis. In the case of natural virosis occurring
in later stages of ontogenesis, this effect has not been
statistically confirmed [36]. The SCE test has also been
used to analyze the mutagenic activity of the maize
rough dwarf virus in some maize lines sensitive to this
pathogen [41].
Results indicate that BSMV infection separately or in
combination with gamma radiation causes a decline in
the mitotic process (produces a mitodepressive effect),
thus inhibiting the cell proliferation process.Cell division
blocking is accompanied by mitotic abnormalities,
such as micronuclei and C-metaphases. The effects of
gamma irradiation are represented by a sinusoidal curve
where complexity is specific to the genotype analyzed.
A similar nonlinear effect was observed by Geraskin
and coworkers [42] upon irradiation of barley seeds with
low doses of gamma rays (10–1,000 mGy). The impact
of radiation on genetic material is well understood.
Rogakou and coworkers [43] explain the genesis of
double-strand breaks under the influence of radiation
as being the direct result of histone H2A phosphorylation
at the level of serine, while suggesting the existence of
other centers sensitive to this factor. Gamma irradiation
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Genotoxicity of barley stripe mosaic virus in infected host plants
of stem cells deficient in the protein kinase Chk1 gene
disrupts the G2/M transition checkpoints [44].
Data from cytogenetic analysis of mitotic divisions
regarding the induction of DNA damage have been
confirmed through assessment of chlorophyll mutations.
It is worth noting that albino plantlets were not observed
in any of the treatments. Chlorophyll mutations,
manifesting themselves as lack of chlorophyll pigments,
were predominantly observable in barley plants of
cv. Unirea in the plot involving viral infection alone or
in combination with gamma irradiation at a dose of
150 Gy. The possibility of inducing chlorophyll mutations
in barley plants using various treatments have been
described previously [42].
BSMV infection produces effects similar to those
induced by gamma rays. It appears the effect of viral
infection is comparable to irradiation doses of 150 or
250 Gy, depending on the genotype analyzed. Combining
viral infection with radiation treatment has demonstrated
nonlinear effects, determined by the interaction of the
three factors of genotype, infection, and radiation dose.
Viral infection has also been found to be involved in
the induction of abnormalities associated with division
spindle aberrations, such as C-mitoses, which reflects
the aneugen nature of the pathogenic agent under
study. A cytological study of mitotic divisions in infected
barley roots indicates a mitodepressive effect of viral
infection and genotoxicity of BSMV.
Acknowledgements
The authors extend their sincere thanks to Mr. G.K.
Lakhman for translating the manuscript into English.
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