INFLUENCE-OF-SEED-TREATMENT-WITH-UV-C-ON-SALINE-STRESS-TOLERANCE-IN-GREEN-BEANS-Phaseolus-vulgaris-L

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INFLUENCEOFSEEDTREATMENT
WITHUV-CONSALINESTRESS
TOLERANCEINGREENBEANS
(Phaseolus...
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INFLUENCE OF SEED TREATMENT
WITH UV-C ON SALINE STRESS
TOLERANCE IN GREEN BEANS
(Phaseolus vulgaris L.)
Journal
J. Biol. Chem.
Environ. Sci., 2014,
Vol. 9 (2): 391- 414
www.acepsag.org
Aboul Fotouh, M.M., F.G. Moawad, H.A. ElNaggar, M.A. Tag El-Din, H.A. Sharaf Eldeen
Agricultural Biochemistry Dept., Fac. Agric., Ain Shams
Univ., Shoubra Elkhema Cairo, Egypt
ABSTRACT
In the present investigation, germinated green bean seeds were
exposed to UV-C (254 nm) for periods of 7, 15, 30 and 60 min, then
grown plants were subjected to saline stress (50 mM NaCl) as a
challenge. Tolerance to saline stress was evaluated by determination of
fresh weight and dry weight of both shoots and roots. Also, biochemical
changes associated with UV-C induced resistance were investigated by
determination of lipid peroxidation, proline concentration and antioxidant
enzymes activities (SOD, CAT, G-POD and APX) in leaves and roots.
Results showed that plants grown from UV treated seeds were less
affected by saline stress which was obvious in increased fresh and dry
weights of shoots and roots as compared with control. However, MDA
showed higher levels in leaves and roots of plants grown from UV treated
seeds. Also, UV seed treatments led to significant increases in proline
concentration in leaves and roots of grown plants under saline or non
saline conditions which contributed to protection from osmotic shock.
Antioxidant enzymes (SOD, CAT, G-POD and APX) exhibited
higher activities in leaves and roots of plants grown from UV treated
seeds. Such effect was more pronounced in roots than leaves. Generally,
it could be concluded that treatment of green bean seeds with UV-C
induced plant tolerance to saline stress via activation of antioxidant
system.
Keywords: UV radiation, Saline stress, Lipid peroxidation, Green bean,
Antioxidant system.
392 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
Abbreviations: ROS, Reactive oxygen species; MDA, Malodialdehyde;
SOD, Super oxide dismutase; CAT, Catalase; G-POD,
Guaiacol peroxidase; APX, Ascorbate peroxides, PVP,
Polyvinyl pyrrolidone.
INTRODUCTION
Due to stratospheric ozone depletion which led to a significant
increase in UV radiation reaches the Earth’s surface, many studies
have focused on the deleterious effect of UV-B on plant growth,
development and productivity Bancroft et al., (2007); Mahdavian et
al., (2008). However, a little number of investigations considered the
possible effect of UV on induced resistance in plant against biotic and
abiotic stress Teklemariam and Blake, (2003); Stevens et al.,
(2004). Also, little information is available on the effect of UV-C seed
treatment on the enzymatic antioxidant system in plant and its impact
on plant stress tolerance. Hence, Challenging plants grown from UVC treated seeds with saline stress as an environmental stress was the
focal point of our investigation.
Saline stress is one of the most limiting factors on agricultural
production. Approximately 20% of the world’s cultivated land and
nearly half of all irrigated lands are affected by salinity Zhu, (2001).
When plants are subjected to saline stress, they suffer from both water
deficit and ionic toxicity causing deficiency in other nutrients Munns,
(2002).
Saline stress leads to accumulation of ROS (O2˙, superoxide
radicals; OH˙, hydroxyl radical; H2O2, hydrogen peroxide and 1O2,
singlet oxygen), causing an oxidative stress. ROS are mainly
generated in chloroplast and mitochondria due to electron transport
processes Chernyak et al., (2006); Schwarzländer et al., (2009);
Xing et al., (2013).
In normal conditions, ROS are produced as byproducts in
metabolic pathways; however there is a balance between ROS and the
antioxidant system in the cell. When plants suffer from biotic or
abiotic stress such as salinity, ROS are excessively produced which
unbalances the cellular redox in favor of oxidized forms, thereby
creating oxidative stress that can damage DNA, inactivates enzymes
and causes lipid peroxidation Gill and Tuteja, (2010).
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
393
Tolerant plants have evolved mechanisms to overcome these
harmful alterations. The results of most studies have shown that
resistance to abiotic stresses is usually correlated with a more efficient
antioxidant system Meratan et al., (2008). Also, proline accumulation
is considered as a biomarker for plant tolerance to drought and salt
stresses due to its osmoprotective function Huang et al., (2009).
Therefore, majority of studies concerned about improvement of saline
stress tolerance by activation of the antioxidant system in plant
Gholizadeh and Kohnehrouz, (2010).
Therefore, the present investigation aimed:
1. To evaluate the ability of UV-C seed treatment to induce saline
stress tolerance in green bean as a model for salt sensitive plants.
2. To study the effect of different doses of UV-C on the antioxidant
systems in green bean and correlate between the biochemical changes
and the level of saline stress tolerance.
MATERIALS AND METHODS
1. Plant material
Green bean seeds (Phaseolus vulgaris, L. cv. paulista, dwarf
French bean) were obtained from Bakker brothers, Holland.
2. UV-C Treatment
Green bean seeds were firstly germinated in petri dishes using
distilled water, then germinated seeds were exposed to 254 nm UV-C
radiation from an artificial source (lamp TUV 15W G158T8 UV-C
long life, Holland Philips special) which was situated at 20 cm over
the seeds. Durations of exposure time were 7, 15, 30 and 60 min.
After treatment, petri dishes containing the germinated seeds were
covered with aluminum foil until sowing to minimize any possible
photoreactivation processes Stevens et al., (1998) and Liu et al.,
(1993).
3. Growth conditions
Treated seeds were sown in polyethylene bags (4×8×13 cm)
containing 700 g acid washed sandy soil (2 seeds/bag) irrigated with
Hoagland nutrient solution for 15 days. After the emergence of the
first trifoliate leaf, plants of each group of UV treatments were divided
into two subgroups: the first subgroup was irrigated with Hoagland
394 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
nutrient solution, the second subgroup was irrigated with the nutrient
solution containing 50 mM NaCl as a source of saline stress. Plants
(45 days-old) were collected and separated to shoots and roots for
determination of growth measurement parameters. Also, other plants
were separated to leaves and roots and stored at -20 ºC for
biochemical analyses.
4. Plant growth measurements
Shoots and roots of plants were separated and analyzed for fresh
weight. Also, dry weight of shoots and roots were determined by
drying at 70 ºC to a constant weight and values were calculated as
gram per plant.
5. Biochemical analysis
5.1. Lipid peroxidation (LPO)
Lipid peroxidation was estimated by measuring the
concentration of malondialdehyde (MDA) according to Heath and
Packer (1968). The MDA concentration was expressed as nmol
MDA.g-1 FW using the extinction coefficient of ε =155 mM-1cm-1.
5.2 Determination of proline concentration
Proline concentration was measured using a ninhydrin
colorimetric method of Troll and Lindsley (1955) as modified by
Petters et al. (1997). Proline concentration was expressed as μg
proline.g-1 Fresh weight (FW).
5.3. Enzymes assays
5.3.1. Enzyme extraction
Frozen tissues of roots and leaves were ground using cold mortar
and pestle and homogenized with cold sodium phosphate buffer
(100mM, pH= 7) containing 1% (w/v) polyvinylpyrrolidone (PVP)
and 0.1 mM EDTA. The extraction ratio was 4 ml extraction buffer
for each one gram of plant tissues. The homogenate was centrifuged at
4500 rpm at 4 ºC for 15 min. The supernatant was used for
measurement of guaiacol peroxidase (G-POD), catalase (CAT),
polyphenol oxidase (PPO), superoxide dismutase (SOD), ascorbate
peroxidase (APX) and phenylalanine ammonia lyase (PAL) activities.
Also, proteins concentration was quantified in the crude extract by the
method of Lowry et al. (1951) using bovine serum albumin as a
standard.
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
395
5.3.2. Superoxide dismutase (SOD) assay
Superoxide dismutase (SOD) (EC 1.15.1.1) assay was based on
the method described by Beyer and Fridovich (1987). The enzyme
activity was expressed as unit.mg-1 protein.
5.3.3. Guaiacol peroxidase (G-POD) assay
Guaiacol peroxidase (EC1.11.1.7) activity was quantified by the
method of Hammerschmidt et al. (1982). The enzyme activity was
expressed as unit.mg-1 protein.
5.3.4. Catalase (CAT) assay
Catalase (CAT) (EC 1.11.1.6) activity was determined according
to the method of Chance and Maehly (1955) as modified by
Cakmak et al. (1993). CAT activity was measured by monitoring the
decrease in absorbance at 240 nm following the decomposition of
H2O2 for 1 min using spectrophotometer (UV-Vis spectrophotometer
UV 9100 B, LabTech). The enzyme activity was expressed as unit.
Mg-1 protein.
5.3.5. Ascorbate peroxidase (APX) assay
Ascorbate peroxidase (APX) (EC 1.11.1.11) activity was
measured according to method of Nakano and Asada (1981). By
monitoring the decrease of absorbance at 290 nm following the
ascorbate oxidation for 3 min using spectrophotometer (UV-Vis
spectrophotometer UV 9100 B, LabTech). The enzyme activity was
expressed as unit.mg-1 protein.
6. Statistical analysis
The data are presented as mean ± SE from three replicates. Data
were subjected to two-way ANOVA to study the effect of seed
treatment with different doses of UV-C radiation on the grown plants
and the effect of saline stress on plants grown from UV-C treated
seeds.
Levels of significance are represented by *P ≤ 0.05, **P ≤ 0.01,
***P ≤ 0.001, and ns (not significant). The means were compared by
the Duncan’s multiple-range test at P ≤ 0.05. Statistical analyses were
performed using SPSS statistical software (IBM SPSS Statistics,
version 20).
396 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
RESULTS AND DISCUSSION
1. Plant growth measurements
Treatment of germinated seeds with UV-C for 30 and 60 min
significantly enhanced shoot fresh weight of grown plants by 33.9 and
82.5% respectively (Fig. 1). Also, there was a positive relationship
between UV doses and root fresh weight values. The highest root
fresh weight (5.913 g) was obtained at the dose of 60 min with an
increase of 94.3% over the control (Fig. 1). Under saline conditions,
all UV treatments except for 60 min failed to cause a significant
difference compared to control in shoot and root fresh weights.
Treatment of germinated seeds with UV-C for 60 min
significantly increased shoots and roots fresh weights of grown plants
by 50.1 and 86.5% respectively over the stressed control.
Analysis of variance test for dry weight showed significant
variations due to UV-C seed treatments, saline stress and their
interaction (Table 1). UV treatments improved shoot dry weight with
increments in a range of 45.9-61.8% over the control (Fig. 1).
Similarly, root dry weight of plants grown from treated seeds
significantly increased. The maximum value (0.480 g) was given at
the dose of 60 min. UV treatments alleviated the deleterious effects of
saline stress on shoot and root dry weights. The greatest shoot dry
weight (0.485 g) was given at the dose of 30 min with an increment of
115.5% over the stressed control (Fig. 1).
Also, it is worth to mention that root dry weight of plants grown
from UV treated seeds enhanced by 74% at the dose of 15 min as
compared with stressed control (Fig. 1).
According to the obtained results it could be concluded that seed
treatment with UV-C improvd plant growth under stressful and non
stressful conditions. These results are consistent with results of
Kacharava et al. (2009) in kidney bean where authors found that
plant height, fresh weight and dry weight increased as a result of 60
and 90 min UV pre-sowing treatment for seeds.
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
397
Table 1. Level of significance of two-way ANOVA test for growth
measurements of shoot and root of Phaseolus vulgaris at UV,
salinity treatments and their interaction.
Figure 1. Effect of green bean seeds treatment with UV-C on fresh
and dry weight (g) of plants grown under saline
conditions (means ± SE). Different letters refer to
significant differences at (P ≤ 0.05).
398 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
Also, similar results were observed in cabbage Brown et el.,
(2001), where the treatment of dry seeds with a hormetic dose of UVC resulted in the heaviest cabbage heads as compared to their control.
These results also appear to support the UV hormesis suggested in the
model of Luckey (1980), who proposed that application of the
optimal doses of UV-C should cause repairable damage or DNA
lesions and this slight shock should activate the repair mechanisms for
radiation induced DNA damage.
Such effect may stimulate vital processes inside the cells like
over compensation of normal metabolic processes, stimulation of the
basic physiological functions that had previously been repressed and
directing the homeostasis of the plant to a positive change which leads
to growth augmentation.
2. Biochemical analysis
2.1. Lipid peroxidation (LPO)
Under non saline conditions, MDA concentration in leaves of
green bean was not significantly affected by UV treatment for seeds.
Among all doses, 15 and 30 min UV treatments elevated MDA level
in leaves with increments of 19.5 and 48.1% over the control
respectively (Fig. 2). However, it seems that the growth of plants in
this group was not affected by the oxidative damage caused by UV
treatment. Also, no significant increase in root MDA levels was
detected as a result of seed irradiation with UV-C except for the dose
of 15 min. The increment was 57.7% over the control (Fig. 2).
In addition, it is noteworthy that MDA concentration was
significantly reduced in roots at the dose of 7 min (Fig. 2).
Interestingly, MDA levels in roots and leaves contrasted with fresh
and dry weight results in plants at the dose of 30 min for leaves and
dose of 15 min for roots. This observation was previously found in
leaves of Arabidopsis challenged with the fungus Botrytis when MDA
levels were correlated with the survival of tissues. It was suggested
that trienoic fatty acids (the major precursors of MDA) contribute to
ROS control via non enzymatic oxidation Mène-Saffranè et al.,
(2009). Furthermore, MDA is not necessarily generated as a result of
lipid peroxidation. It was observed that Arabidopsis mutants lacking
trienoic fatty acids (TFAs) contained 25% of MDA pool present in
wild type plants, referring to existence of other origins for MDA
Weber et al., (2004).
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
399
Under saline conditions, no significant increase in leaf MDA
concentration was detected in almost all treatments as a result of salt
stress. However, plants grown from UV treated seeds for 60 min showed
a considerable elevation in leaf MDA levels as compared to unstressed
plants of the same treatment. On the contrary, MDA levels were
significantly affected by UV seed treatment (Table 2 and Fig. 2). A
gradual increase was observed in leaves of plants grown from UV treated
seeds as compared with stressed control.
Contrary to leaves, the effect of saline stress on MDA concentration
was more pronounced in roots. Saline stress resulted in significant
increases in MDA levels as compared to unstressed plants (Table 2 and
Fig. 2). Also, treatment of germinated seeds with doses of 30 and 60 min
significantly increased MDA concentration as compared with stressed
control with increments of 44.2 and 40.9% respectively (Fig. 2).
Table 2. Level of significance of two-way ANOVA test for Lipid
peroxidation (LPO) and proline concentration in leaves and roots of
Phaseolus vulgaris at UV, salinity treatments and their interaction.
400 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
The results together indicated that treatment of seeds with UV-C
did not reduce MDA concentration in leaves and roots of green bean
under saline conditions. However, rise in MDA levels did not reflect
the enhanced growth of plants grown from UV treated seeds under
saline conditions.
MDA is a secondary product of lipid peroxidation, therefore it
can be used as an index for the oxidative damage accompanied by
biotic and abiotic stress in plant cells Hodges et al., (1999). In
addition, MDA is a highly reactive molecule and reacts rapidly with
DNA and proteins, causing modification to their structures
Refsgaard, et al., 2000; Marnett, (2002). However, it was found that
the expression of 26 genes was altered as a response to application of
exogenous MDA. The expression of these genes was directed towards
the genes that have roles in abiotic stress like SODFE gene which
encodes for SOD Weber et al., (2004). Such response suggests an
important role that MDA plays under environmental stresses.
Moreover, it was stated by more than evidence that MDA exists
also in healthy tissues. For instance, Mène-Saffranè et al. (2007)
found that part of MDA pool was concentrated in meristematic cells
(cell division region) of the root of Arabidopsis seedlings and the
majority of this MDA was not derived from TFAs. Thus, the enhanced
growth in spite of high MDA levels in the present investigation may
be attributed to the vital role of MDA in directing cells to induce
survival programs.
2.2. Proline concentration
Treatment of green bean seeds with UV-C did not affect
markedly proline levels in leaves (Fig. 3). Also, proline levels in roots
were not influnced by treatment of germinated seeds with UV-C.
Under salt stress, foliar proline concentration increased in all
treatments as compared to unstressed plants in the same group. For
instance, the increment in stressed control plants was 51.7% over the
unstressed plants (Fig. 3).
Plants grown from UV treated seeds exhibited higher proline
concentrations as compared with stressed controls. All UV treatments
except for 60 min attained a significant increase over the stressed
control. The maximum increment (47.5 %) was observed at the dose
of 15 followed by doses of 7 and 30 min with increments of 46.2 and
43.0 % respectively over the stressed control (Fig. 3).
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
401
Similarly, roots responded to salt stress by increasing proline
concentration in control and all treatments. Nevertheless, UV seed
treatment at the doses of 15 and 60 min drastically elevated proline
concentration as compared with stressed control plants. The
increments were 130.4 and 107.5% respectively (Fig. 3).
Generally, it could be concluded that UV seed treatment nonsignificantly increased proline levels in most cases in both leaves and
roots. Individual treatment of saline stress led to a significant increase
in proline in leaves and roots. The effect of interaction between UV
seed treatment and saline stress on increasing proline levels was
higher than individual treatment of both. These results are in
agreement with Rajabbeigi et al. (2013) as they found that UV treated
plants showed no significant change in proline contents, while proline
levels dramatically increased as a result of drought stress. Moreover,
the combined effect of UV and drought stresses revealed a
pronounced increase in proline content more than the individual
treatments of both stresses. In conclusion, seed treatment with UV
enhanced plant tolerance against saline stress by increasing proline
synthesis in leaves and roots.
Apart of being an osmoregulator Ambikapathy et al., (2002),
proline also protects proteins from damage and enhances enzymes
activities Sharma and Dubey, (2005); Mishra and Dubey, (2006);
Huang et al., (2009). Moreover, proline was found to act as a ROS
scavenger Siripornadulsil et al., (2002). In addition, high levels of
proline synthesis maintains NADP+/NADPH ratio in the cell as it is in
the normal conditions Hare and Cress, (1997).
402 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
2.3. Enzymes assays
2.3.1. SOD activity
No significant change was observed between SOD activities in
leaves of control and plants grown from UV-C treated seeds at the
dose of 7 min. Also, treatment of germinated seeds with the dose of 15
min was effective to enhance SOD activity by 20.6%. In contrast,
doses of 30 and 60 min significantly reduced SOD activity by 23.4
and 58% respectively (Fig. 4). In roots, exposing germinated seeds to
UV-C did not affect SOD levels at the doses of 7,30 and 60 min,
whereas 15 min treatment led to a considerable decrease by 21.2%
(Fig. 4).
Under saline conditions, SOD activities exhibited a gradual
decrease by increasing UV doses in leaves. Also, Fig. 4 shows that
saline stress had an inhibitory effect on SOD in roots of control plants
and plants grown from UV treated seeds. Furthermore, SOD levels in
roots of plants grown from UV treated seeds were lower than control
except for plants grown from treated seeds at the dose of 7 as there
was no significant change between this treatment and control. Also, it
is worth mentioning that similar to leaves, SOD activity in roots of
plants grown from treated seeds decreased gradually with increasing
doses of UV under saline conditions (Fig. 4). Such observation may
explain the elevation of MDA levels in plants at higher doses of UVC.
Moreover, according to to Rybus-Zając and Kubiś (2010), it
was expected that plants grown from UV treated seeds should elevate
SOD in leaves and roots of grown plants. However, the effect of UVC treatment on SOD activity varied (from inhibition to induction) with
different doses. Also, the impact of UV treatment on SOD levels
varied in different organs. Therefore, it could be observed that SOD
activity in leaves was higher than control at the dose of 15 min, while
there were no significant differences between SOD activities in
control roots and the roots of plants grown from UV treated seeds at
the doses of 7, 30 and 60 min. In addition, UV treatment at the dose of
60 min suppressed SOD in leaves of plants grown from germinated a
seed which was not observed in the roots.
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
403
The effect of UV on SOD activity in plants was inspected by
many investigators and the results were different. Strid et al. (1994)
noticed that chloroplastic SOD transcripts were reduced as a result of
exposure of pea seedlings to UV. Also, Chen (2009) demonstrated
that elevated UV enhanced MDA concentrations and reduced SOD
activities in Isatis indigotica seedlings. On the other hand, SOD levels
were increased in Abelmoschus esculentus L. (Okra) plants as after
exposure to UV-B Kumari et al., (2009).
Other studies showed that UV treatment did not change SOD
activity Vyšniauskienė and Rančelienė, (2014). Moreover, factors
like temperature and the seedlings age should be taken in
consideration in interpreting the effect of UV on SOD activity in
plants Takeuchi et al., (1996).
Table 3. Level of significance of two-way ANOVA test for
antioxidant enzymes activities in leaves and roots of Phaseolus
vulgaris at UV, salinity treatments and their interaction.
404 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
2.3.2. CAT activity
Treatment of green bean seeds with UV-C led to a significant
reduction in CAT activity in leaves of plants at all treatments. The
reductions were in a range of 11.6% at the dose of 15 min treatment
for germinated seeds to 43.5% at the dose of 60 min (Fig. 5).
In contrast, opposite results were observed in roots. UV-C seed
treatment induced CAT in roots of grown plants at the doses of 7, 15
and 60 min. The greatest increment (3.5-fold increase) was observed
at the dose of 60 min followed by dose of 15 min which led to a 1.6fold increase over the control (Fig. 5).
Saline stress stimulated CAT activity in control leaves with
increment of 23.2% over unstressed plants. Nevertheless, it was
observed that CAT activity showed a noticeable increase over stressed
control at the doses of 15 and 30 min under saline conditions. The
increments were 49.4 and 42.4% for doses of 15 and 30 min
respectively (Fig. 5). Similarly, all UV treatments attained a
significant increase over stressed control in CAT activity in roots
under saline conditions. The increments were in a range of 58.3 to
258.3%.
According to the obtained results, it could be concluded that the
effect of UV-C treatment on CAT induction was more pronounced in
roots. In addition, CAT was repressed in leaves of plants grown from
UV treated seeds. These results are concomitant with decreased SOD
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
405
activities. The balance between SOD and CAT or APX activity is
crucial for conserving steady state levels of H2O2 Mittler, (2002).
Also, it should be noticed that there is integration between APX
and CAT activities particularly at the dose of 7 min as APX
compensated for the CAT inhibition. Such observation was previously
reported in Trigonella after exposure to irradiation stress Al-Rumaih
and Al-Rumaih, (2008).
In the presnt study, seed treatment with UV-C led to a dramatic
increase in CAT activity under saline conditions in roots. Yasar et al.
(2008) reported that CAT activity increased in salt-tolerant cultivar of
Phaseolus vulgaris under salt stress conditions with a rate greater than
salt-sensitive cultivar. Thus, increased CAT activity in roots of plants
grown from UV treated seeds provided better protection from salt
stress.
2.3.3. G-POD activity
Treatment of germinated seeds led to significant reductions in
leaves of grown plants under non saline conditions at the doses of 7,
15, 30 min. By contrast, UV treatment at the dose of 60 min
significantly increased G-POD activity by 59.1% over the control
(Fig. 6). Furthermore, G-POD showed 1.1-fold increase in roots of
plants grown from UV treated seeds at the dose of 60 min when
compared with control (Fig. 6).
Under saline conditions, G-POD activities in leaves were
elevated at all treatments except for dose of 60 min. Moreover, GPOD activity fluctuated with increasing doses of UV and the highest
activities were observed at the doses of 7 and 30 min with increments
of 22.6 and 8.6% respectively (Fig. 6).
Also, saline stress elevated G-POD in roots of plants at all
treatments. Similarly, UV treatment of germinated seeds raised GPOD in roots at all doses when compared with stressed control. The
increments ranged from 31.9% at the dose of 7 min to 384.1% at the
dose of 15 min (Fig. 6).
406 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
In the present investigation, although plants grown from UV
treated seeds exhibited lower G-POD activities under non saline
conditions in leaves and roots, their response to salt stress with regard
to G-POD activity was higher than control. Such effect may be
attributed to priming effect which makes plants response to abiotic
stress more rapid and stronger.
One of the hypotheses proposed to explain priming is
accumulation of inactive proteins that play important roles in signal
amplification then challenging with abiotic stress should activate these
dormant signaling proteins, leading to signal amplification initiation
more rapidly and robustly than unprimed plants Conrath, (2011).
In this context, Kubiś and Rybus-Zając (2008) reported that UVpretreated cucumber seedlings exhibited higher antioxidant enzyme
activities under drought stress and suggested that one of the stresses
reduced the adverse effects of the other. Also, results show that roots were
affected by UV seed irradiation more than leaves under saline stress.
2.3.4. APX activity
Exposure of germinated seeds to UV-C for 7 min led to a
significant increase in APX activity in leaves of grown plants with an
increment of 7.8% over the control. By contrast, APX activity
decreased gradually with increasing UV doses, exhibiting lower
activities than control (Fig. 7). In roots, opposite results were observed
as APX exhibited higher activities at the doses of 7, 30 and 60 min
J. Biol. Chem. Environ. Sci., 2014, 9 (2), 391-414
407
when compared with control. The increments were 69.2, 19.5 and
73.4% over the control respectively (Fig.7).
Also, APX showed higher activity in leaves as response to saline
stress in control plants. By contrast, APX activity was negatively
affected by saline stress in leaves of plants grown from UV treated
seeds at the doses of 7 and 15 min, whereas opposite results were
noticed at the doses of 30 and 60 min. Generally, treatment of seeds
with UV led to a gradual decline in APX activity in leaves under
saline conditions when compared with control (Fig. 7).
In roots, saline stress resulted in elevating APX activity in
control and most treatments. Also, application of UV-C on germinated
seeds was effective in inducing APX activity in roots under saline
conditions. The increments were significant in comparison with
stressed control at the doses of 15, 30 and 60 min. The maximum
activity (0.328 Unit.mg-1 protein) was given at the dose of 15 min with
an increment of 43.2% over the control (Fig. 7).
Induction of APX as a result of UV treatment in leaves at the
dose of 7 min and in roots at almost all doses under non saline
conditions is consistent with results of Zacchini and de Agazio
(2004) who reported that exposure of tobacco callus to UV-C led to an
enhancement in antioxidant enzymes (APX and G-POD) after 24 h
from the treatment. On the contrary, Nottaris et al. (1997) reported
that APX activity decreased in sugar beet calli after exposure to UV-C
which agrees with the observed results of APX activity at doses higher
than 7 min under saline or non saline conditions.
408 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS
In this context, Feng et al. (2009) declared that plant responses
to enhanced UV with regard to APX levels depend on genetic
backgrounds and developmental stage.
Under saline conditions, APX levels increased in both control
and plants grown from UV treated seeds. However, the increment was
higher in control leaves, whereas roots of plants grown from UV
treated seeds exhibited greater APX levels. However, it was found that
CAT and G-POD activities compensated for APX activity decrements
in leaves under saline conditions.
According to the obtained results, it could be concluded that the
exposure of green bean seeds to UV-C enhanced their tolerance to
saline stress via activation of the antioxidant system and accumulation
of proline in leaves and roots which lessened the effect of osmotic
stress. However, this effect varied among the applied doses. Also, it
could be concluded that the optimal dose for green bean seeds was at
60 min which achieved the best growth in shoots and roots of grown
plants under saline or non saline conditions.
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‫‪414 INFLUENCE OF SEED TREATMENT WITH UV-C ON SALINE STRESS‬‬
‫ﺗﺄﺛﻴﺮ ﻣﻌﺎﻣﻠﺔ اﻟﺒﺬور ﺑﺎﻷﺷﻌﺔ ﻓﻮق اﻟﺒﻨﻔﺴﺠﻴﺔ ﻋﻠﻰ ﺗﺤﻤﻞ اﻹﺟﻬﺎد اﻟﻤﻠﺤﻰ ﻓﻰ‬
‫اﻟﻔﺎﺻﻮﻟﻴﺎ اﻟﺨﻀﺮاء‬
‫ﻣﺤﻤﺪ ﻣﺤﻤﻮد أﺑﻮ اﻟﻔﺘﻮح – ﻓﺎروق ﺟﻨﺪى ﻣﻌﻮض – ﺣﻤﺪى ﻋﻠﻰ اﻟﻨﺠﺎر –‬
‫ﻣﻤﺪوح أﺑﻮ ﻣﺴﻠﻢ ﺗﺎج اﻟﺪﻳﻦ – هﺎﻧﻰ ﻋﺒﺪ اﻟﺨﺎﻟﻖ ﺷﺮف اﻟﺪﻳﻦ‬
‫ﻗﺴﻢ اﻟﻜﻴﻤﻴﺎء اﻟﺤﻴﻮﻳﺔ اﻟﺰراﻋﻴﺔ – آﻠﻴﺔ اﻟﺰراﻋﺔ – ﺟﺎﻣﻌﺔ ﻋﻴﻦ ﺷﻤﺲ – ﺷﺒﺮا اﻟﺨﻴﻤﺔ –‬
‫اﻟﻘﺎهﺮة – ﻣﺼﺮ‬
‫ﻓ ﻰ ه ﺬﻩ اﻟﺪراﺳ ﺔ ﺗ ﻢ ﺗﻌ ﺮﻳﺾ اﻟﺒ ﺬور اﻟﻤ ﺴﺘﻨﺒﺘﺔ ﻟﻨﺒ ﺎت اﻟﻔﺎﺻ ﻮﻟﻴﺎ اﻟﺨ ﻀﺮاء ﻟﻸﺷ ﻌﺔ ﻓ ﻮق‬
‫اﻟﺒﻨﻔ ﺴﺠﻴﺔ )‪ (UV-C‬ﻟﻤ ﺪة ‪ 60 ،30 ،15 ،7‬دﻗﻴﻘ ﺔ ﺛ ﻢ ﺗ ﻢ ﺗﻌ ﺮﻳﺾ اﻟﻨﺒﺎﺗ ﺎت اﻟﻨﺎﻣﻴ ﺔ ﻟﻈ ﺮوف‬
‫اﻹﺟﻬﺎد اﻟﻤﻠﺤ ﻰ )‪ 50‬ﻣﻴﻠﻠﻴﻤ ﻮﻟﺮ آﻠﻮرﻳ ﺪ اﻟ ﺼﻮدﻳﻮم(‪ .‬ﺗ ﻢ ﺗﻘﻴ ﻴﻢ ﺗﺤﻤ ﻞ اﻟﻨﺒﺎﺗ ﺎت ﻟﻺﺟﻬ ﺎد اﻟﻤﻠﺤ ﻰ‬
‫ﺑﺘﻘﺪﻳﺮ اﻟﻮزن اﻟﻄﺎزج و اﻟﺠﺎف ﻟﻜﻞ ﻣﻦ اﻟﻤﺠﺎﻣﻴﻊ اﻟﺨﻀﺮﻳﺔ و اﻟﺠﺬرﻳﺔ‪ .‬آﻤﺎ ﺗﻢ ﻗﻴ ﺎس اﻟﺘﻐﻴ ﺮات‬
‫اﻟﻜﻴﻤﻴﺎﺋﻴ ﺔ اﻟﻤ ﺼﺎﺣﺒﺔ ﻟﻠﻤﻘﺎوﻣ ﺔ اﻟﻤ ﺴﺘﺤﺜﺔ ﺑﺎﻷﺷ ﻌﺔ ﻓ ﻮق اﻟﺒﻨﻔ ﺴﺠﻴﺔ ﻣ ﻦ ﺧ ﻼل‪ :‬ﺗﻘ ﺪﻳﺮ أآ ﺴﺪة‬
‫اﻟﻠﻴﺒﻴ ﺪات – ﺗﺮآﻴ ﺰ اﻟﺒ ﺮوﻟﻴﻦ ‪ -‬ﻗﻴ ﺎس ﻧ ﺸﺎط اﻹﻧﺰﻳﻤ ﺎت اﻟﻤ ﻀﺎدة ﻟﻸآ ﺴﺪة )ﺳ ﻮﺑﺮ أآ ﺴﻴﺪ‬
‫دﻳ ﺴﻤﻴﻮﺗﻴﺰ – آﺘ ﺎﻟﻴﺰ – ﺟﻮاﻳﻜ ﻮل ﺑﻴﺮوآ ﺴﻴﺪﻳﺰ – أﺳ ﻜﻮرﺑﺎت ﻳﺮوآ ﺴﻴﺪﻳﺰ( ﻓ ﻰ اﻷوراق و‬
‫اﻟﺠﺬور‪ .‬أوﺿﺤﺖ اﻟﻨﺘﺎﺋﺞ أن اﻟﻨﺒﺎﺗﺎت اﻟﻨﺎﻣﻴﺔ ﻣﻦ اﻟﺒﺬور اﻟﻤﻌﺎﻣﻠﺔ ﺑﺎﻷﺷﻌﺔ ﻓ ﻮق اﻟﺒﻨﻔ ﺴﺠﻴﺔ آﺎﻧ ﺖ‬
‫أﻗﻞ ﺗﺄﺛﺮا ﺑﺎﻹﺟﻬ ﺎد اﻟﻤﻠﺤ ﻰ و ذﻟ ﻚ آ ﺎن واﺿ ﺤﺎ ﻓ ﻰ ارﺗﻔ ﺎع اﻟ ﻮزن اﻟﻄ ﺎزج و اﻟﺠ ﺎف ﻟﻜ ﻞ ﻣ ﻦ‬
‫اﻟﻤﺠ ﺎﻣﻴﻊ اﻟﺨ ﻀﺮﻳﺔ و اﻟﺠﺬرﻳ ﺔ ﺑﺎﻟﻤﻘﺎرﻧ ﺔ ﺑ ﺎﻟﻜﻨﺘﺮول‪ .‬و ﻣ ﻊ ذﻟ ﻚ ﻓ ﺈن ﻣ ﺴﺘﻮﻳﺎت اﻟﻤ ﺎﻟﻮن داى‬
‫أﻟﺪهﻴﺪ أﻇﻬﺮت ارﺗﻔﺎﻋﺎ ﻓﻰ أوراق و ﺟ ﺬور اﻟﻨﺒﺎﺗ ﺎت اﻟﻨﺎﻣﻴ ﺔ ﻣ ﻦ اﻟﺒ ﺬور اﻟﻤﻌﺎﻣﻠ ﺔ ﺑﺎﻷﺷ ﻌﺔ ﻓ ﻮق‬
‫اﻟﻨﻔ ﺴﺠﻴﺔ‪ .‬أﻳ ﻀﺎ أدت ﻣﻌﺎﻣﻠ ﺔ اﻟ ﺬور ﺑﺎﻷﺷ ﻌﺔ ﻓ ﻮق اﻟﺒﻨﻔ ﺴﺠﻴﺔ إﻟ ﻰ زﻳ ﺎدات ﻣﻌﻨﻮﻳ ﺔ ﻓ ﻰ ﺗﺮآﻴ ﺰ‬
‫اﻟﺒﺮوﻟﻴﻦ ﻓﻰ أوراق و ﺟﺬور اﻟﻨﺒﺎﺗﺎت ﺗﺤﺖ اﻟﻈﺮوف اﻟﻤﻠﺤﻴ ﺔ و ﻏﻴ ﺮ اﻟﻤﻠﺤﻴ ﺔ و اﻟ ﺬى أﺳ ﻬﻢ ﻓ ﻰ‬
‫ﺣﻤﺎﻳﺘﻬﺎ ﻣﻦ اﻹﺟﻬﺎد اﻷﺳﻤﻮزى‪ .‬آﻤﺎ أﻇﻬﺮت اﻹﻧﺰﻳﻤﺎت اﻟﻤﻀﺎدة ﻟﻸآﺴﺪة ارﺗﻔﺎﻋ ﺎ ﻓ ﻰ ﻧ ﺸﺎﻃﻬﺎ‬
‫ﻓ ﻰ أوراق و ﺟ ﺬور اﻟﻨﺒﺎﺗ ﺎت اﻟﻨﺎﻣﻴ ﺔ ﻣ ﻦ اﻟﺒ ﺬور اﻟﻤﻌﺎﻣﻠ ﺔ ﺑﺎﻷﺷ ﻌﺔ ﻓ ﻮق اﻟﺒﻨﻔ ﺴﺠﻴﺔ‪ .‬و آ ﺎن ه ﺬا‬
‫اﻟﺘ ﺄﺛﻴﺮ ﻣﻠﻤﻮﺳ ﺎ أآﺜ ﺮ ﻓ ﻰ اﻟﺠ ﺬور ﻋ ﻦ اﻷوراق‪ .‬ﻋﻤﻮﻣ ﺎ ﻓﺈﻧ ﻪ ﻳﻤﻜ ﻦ اﺳ ﺘﻨﺘﺎج أن ﻣﻌﺎﻣﻠ ﺔ ﺑ ﺬور‬
‫اﻟﻔﺎﺻﻮﻟﻴﺎ اﻟﺨﻀﺮاء ﺑﺎﻷﺷﻌﺔ ﻓﻮق اﻟﺒﻨﻔﺴﺠﻴﺔ أدى إﻟﻰ ﺣﺚ اﻟﻨﺒﺎﺗﺎت ﻋﻠﻰ ﺗﺤﻤﻞ اﻹﺟﻬﺎد اﻟﻤﻠﺤ ﻰ‬
‫ﻣﻦ ﺧﻼل ﺗﻨﺸﻴﻂ اﻟﻨﻈﺎم اﻟﻤﻀﺎد ﻟﻸآﺲ‪.‬‬
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