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© 2017 The Japan Mendel Society Cytologia 82(3): 279 –286
Role of Potassium Nitrate (KNO3) in Alleviation of
Detrimental Effects of Salt Stress on Some Physiological
and Cytogenetical Parameters in Allium cepa L.
Kürşat Çavuşoğlu1*, Sevilay Cadıl1 and Dilek Çavuşoğlu2
1 Department of Biology, Faculty of Arts and Science, Süleyman Demirel University, Isparta 32260, Turkey
2 Department of Food Processing, Atabey Vocational School, Süleyman Demirel University, Isparta 32670, Turkey
Received July 22, 2016; accepted March 15, 2017
Summary In this work, the effects of potassium nitrate (KNO3) on the seed germination, seedling growth
(radicle length, radicle number and fresh weight), mitotic activity and chromosomal aberrations of Allium cepa L.
germinated under both normal conditions and salt stress were studied. The final germination percentages, radicle
lengths, radical numbers and fresh weights of onion seeds germinated in the medium with KNO3 alone were
statistically the same as ones of the control seeds germinated in distilled water medium. In addition, the mitotic
index in root tip meristems of A. cepa seeds germinated in the medium with KNO3 alone demonstrated a decrease
according to ones of the control seeds germinated in distilled water medium, while their frequency of chromo-
somal aberrations showed an increase according to the control. On the other hand, salt stress considerably inhib-
ited the seed germination and seedling growth of A. cepa. Furthermore, it markedly decreased the mitotic index
in root tip meristems of the seeds and increased the number of chromosomal aberrations. The detrimental effects
of salt on the seed germination, seedling growth, mitotic activity and chromosomal aberrations was dramatically
alleviated in varying degrees by KNO3 application.
Key words Chromosomal abnormality, Mitotic index, Potassium nitrate, Salt stress, Seed germination, Seedling
growth.
Accumulation of excess salts in the root zone result-
ing in a partial or complete loss of soil productivity is
a worldwide phenomenon. Approximately 20% of the
worlds cultivated land, which accounts for over 6% of
the world total area, is threatened by salinity. Five hun-
dred thousand hectares of agricultural areas in Turkey
are affected by salinization. Salt-affected soil in Turkey
is especially located in the Central South, Central North
and Mediterranean regions (Haktanır et al. 2004). The
salt-affected soils contain excess salts which affect
plants by decreasing the osmotic potential of the soil so-
lution (osmotic stress), interfering with normal nutrient
uptake, inducing ionic toxicity, and associating nutrient
imbalances (Dudley 1992, An et al. 2003). Processes
such as seed germination, seedling growth and vigour,
vegetative growth, flowering and fruit set are adversely
affected by high salt concentration, ultimately causing
diminished economic yield and also quality of produc-
tion (Sairam and Tyagi 2004).
The most efficient way to minimize the detrimental
effects of salinity on plant breeding is the develop-
ment of varieties with high salinity tolerance. Hence,
researchers have used various plant growth regulators
and vitamins to reduce or eradicate negative effects of
salinity on seed germination (Duan et al. 2008, Emam
and Helal 2008), seedling growth (Çavuşoğlu and Kabar
2007, Çavuşoğlu and Karaferyeli 2015) and mitotic
activity (Tabur and Demir 2009, 2010a). In addition,
most researchers agree that the best way to proceed
with breeding would be via pyramiding different use-
ful physiological traits. However, in spite of substantial
efforts, the outcomes are still disappointingly poor due
to the physiological and genetic complexity of this trait,
the lack of reliable screening tools and most impor-
tantly the lack of a comprehensive understanding of the
mechanisms behind salinity tolerance (Zhu et al. 2016).
Recently, some potassium compounds such as potassium
nitrate (KNO3) have started being used to decrease the
toxicity of salinity (Jabeen and Ahmad 2011, Hamayun
et al. 2014). Potassium (K) acts as a very essential and
important nutrient for plant growth and development. It
is necessar y in plants to improve the efficiently of pho-
tosynthesis and use of water (Ross 2001). Application of
K to plants under saline conditions enhances the growth
of the plants and decreases the effect of salinity (Safaa
et al. 2013).
The Allium test has important advantages (Rank 2003,
Kuras et al. 2006) and has been used for many years in
investigating physical and chemical mutagenesis, pollut-
ant agents, plant extracts, and similar active materials
cytogenetic effects in mitotic cell division. It is stated
* Corresponding author, e-mail: kursatcavusoglu@sdu.edu.tr
DOI: 10.1508/cytologia.82.279
280 K. Çavuşoğlu et al. Cytologia 82(3)
that the Allium test exhibits similar results with mam-
malian test systems (El-Shahaby et al. 2003, Teixeira
et al. 2003). Although there are many published studies
about the effects of KNO3 on the seed germination and
seedling growth under normal conditions (Ramzan et al.
2010, Bian et al. 2013, Lara et al. 2014), unfortunately,
the protective mechanisms of KNO3 on salt stress in
plants is still unknown. The present study was designed
to examine the influences of KNO3 in the reducing of
detrimental effects of salt stress on the seed germina-
tion, seedling growth, mitotic activity and chromosomal
aberrations of Allium cepa L.
Materials and methods
Seeds, salt and KNO3 concentrations
In this study, Allium cepa L. seeds were used. Salt
(NaCl) concentration used was 0.15 M. KNO3 concentra-
tion used in the experiments was 40 mg L1. KNO3 was
obtained from Sigma-Aldrich Company, United King-
dom. KNO3 and NaCl concentrations were determined
in a preliminary investigation conducted by us.
Germination of the seeds
Germination experiments were carried out at a con-
stant temperature (20C), in the dark in an incubator.
Healthy and approximately equal-sized A. cepa seeds
were selected. The seeds were sterilized with 2.5% so-
dium hypochloride solution for 10 min and washed for
24 h in ultra-distilled water. Twenty seeds from each
treatment group were placed into plastic containers. The
seeds were divided into four groups:
➢Group I (control) was treated with distilled water, for
seven consecutive days.
➢Group II was treated with 0.15 M NaCl alone, for
seven consecutive days.
➢Group III was treated with a 40 mg L1 dose of KNO3,
for seven consecutive days.
➢Group IV was treated with a 40 mg L1 dose of
KNO3+ 0.15 M NaCl, for seven consecutive days.
Plastic containers were placed into an incubator for
germination. It was assumed that the radicle should be
10 mm long for germination to take place. At the end of
the seventh day, after determination of the final germi-
nation percentages, radicle numbers were also recorded,
and radicle lengths of the seedlings were measured in
mm, and in addition, the fresh weights in g/seedling
were determined. All experiments were repeated three
times.
Cytological and statistical analysis
Root tips of germinated A. cepa after several days
were excised (1–1.5 cm segment) for cytogenetic analy-
sis. Then, they were pretreated with saturated para-di-
chlorobenzene for 4 h, fixed in solution of ethanol–acetic
acid (3 : 1) overnight at room temperature and stored
at 4C in 70% ethanol until used. The root tips were
hydrolysed in 1 N HCl at 60C for 15 min, stained with
Feulgen for 1–1.5 h, smashed in a drop of 45% acetic
acid and squashed (Sharma and Gupta 1982). After 24 h,
microscopic slides were made permanent by mounting
in balsame. The mitotic phases and mitotic aberrations
were photographed (100) with a digital camera (Olym-
pus C-5060) mounted on an Olympus CX41 microscope.
Mitotic index, i.e., percentage of dividing cells scored
was evaluated by analysing at least 30000 cells per treat-
ment (approx. 10000 per slide). Chromosomal abnormali-
ties were calculated for each concentration as the percent-
age of 2000 dividing cells counted. Statistical evaluation
concerning all parameters was realized by using SPSS
program according to Duncans multiple range test.
Results
Effects of KNO3 on seed germination and seedling
growth
The germination percentage, radicle length, radicle
number and fresh weight of group III seeds treated with
KNO3 statistically showed the same values as group I
(control) seeds germinated in distilled water medium
(Table 1).
Salt exhibited an inhibitive effect on all examined
growth parameters. For example, group I (control) seeds
germinated in distilled water medium displayed 100%
germination on the seventh day while this value became
32% in group II seeds germinated in 0.15 M salinity. In
other words, salt prevented 68% of the germination of A.
cepa seeds. KNO3 application markedly alleviated the
inhibitive effect of salt stress on the seed germination.
Group IV seeds treated with KNO3 demonstrated 80%
germination in the mentioned salt level. Finally, A. cepa
seeds showed a performance such as germinated under
normal conditions, are not in saline conditions (Fig. 1).
KNO3 also continued its success on the seedling growth
parameters such as the radicle length, radicle number
and fresh weight. The radicle length, radicle number and
Table 1. Effect of KNO3 on some growth parameters of Allium cepa
L.
Groups
Growth parameters
Germination
percentage
(%)
Radicle length
(mm)
Radicle
number
Fresh weight
(g/seedling)
Group I *1000.0c72.9 2.4c41.91.0c14.21.4c
Group II 322.8a20.11.1a9.1 0 .1a9.00.0a
Group III 1000.0c68.93.3c39.3 2.3c13.3 0.5c
Group IV 800.0b55.10.4b32.23.9b11.30.9b
* The difference between values with the same letter in each
column is not significant at the level 0.05 (SD). Group I (con-
trol) was treated with distilled water; Group II was treated
with 0.15 M NaCl alone; Group III was treated with a 40 mg L1
dose of KNO3; Group IV was treated with a 40 mg L1 dose of
KNO3+ 0.15 M NaCl.
2017 Physiological and Cytogenetical Effects of KNO3 on Salinity 281
fresh weight of group II seedlings grown in 0.15 M salin-
ity were 20.1 mm, 9.1 and 9.0 g, respectively, while these
values became 55.1 mm, 32.2 and 11.3 g, respectively, in
group IV seedlings treated with KNO3 (Table 1).
Effects of KNO3 on the mitotic index and chromosomal
aberrations
Mitotic activity expressed as mitotic index (MI) de-
creased at 0.15 M salt concentration (group II) as com-
pared to those of group I (control) samples germinated in
distilled water. At the same time, the salt concentration
caused a significant increase of chromosomal aberra-
tions in root tips of A. cepa. For instance, while mitotic
index and chromosomal aberrations were 5.1 and 11.4 at
control (group I), respectively, they were 2.6 and 54.1,
respectively, at 0.15 M NaCl concentration (Table 2).
Mitotic index of group III seeds germinated in the me-
dia with KNO3 alone partly reduced according to group
I samples, and this treatment caused an approximately
four-fold increase of chromosomal aberrations. However,
KNO3+NaCl application (Group IV) showed a perfectly
good performance in ameliorating the negative effects of
salinity on the mitotic index (7.5) and chromosomal ab-
errations (36.2). Statistically, all values mentioned here
are substantially significant (Table 2).
Normal and abnormal mitotic phases observed during
microscopic examination of A. cepa root tip meristem
cells were indicated in Figs. 2 and 3. The most striking
aberrations observed in all applications were micronu-
cleus, irregular prophase, uncoiling chromosome, sticky
chromosome, irregular anaphase, bridge in anaphase,
fault polarization in anaphase, vagrant chromosome in
anaphase, lagging chromosome in anaphase, alignment
anaphase, fault polarization in telophase, and vagrant
chromosome in telophase (Fig. 3a–l). The majority of
chromosomal abnormalities in root tip cells treated with
KNO3 or salt were determined as disorderly prophase
(Fig. 3b), uncoiling chromosome (Fig. 3c) and bridge in
anaphase (Fig. 3f).
Discussion
Physiological and cytogenetical effects of KNO3 under
normal conditions
Unless there are generally stress conditions, there is
no need to add exogenously any plant growth regulator
in germination process. Exogenous growth regulator ap-
plication may cause a positive or negative effect on the
seed germination and seedling growth under non-stress
conditions (Çavuşoğlu and Kabar 2008, Çavuşoğlu and
Bilir 2015, Çavuşoğlu and Ergin 2015). On the other
hand, there are enough studies about the effects of KNO3
on the seed germination and seedling growth under
normal conditions. However, in these studies, it could
not reach a consensus. Thus, we also wanted to test the
effects of KNO3 application on the seed germination and
Fig. 1. The germination situations at the end of the seventh day of Allium cepa L. seeds. Group I (control) was treated with dis-
tilled water; Group II was treated with 0.15 M NaCl alone; Group III was treated with a 40 mg L1 dose of KNO3; Group
IV was treated with a 40 mg L1 dose of KNO3+ 0.15 M NaCl. Scale bar =1 cm.
Table 2. Effect of KNO3 on mitotic index and frequency of chromo-
somal aberrations in Allium cepa L. root tip meristems.
Groups Mitotic index (%) Chromosome aberration (%)
Group I *5.1 0.6c11.4 0.9a
Group II 2.60.6a54.10.7d
Group III 3.80.9b46.80.4c
Group IV 7.50.4d36.2 1.1b
* The difference between values with the same letter in each
column is not significant at the level 0.05 (SD). Group I (con-
trol) was treated with distilled water; Group II was treated
with 0.15 M NaCl alone; Group III was treated with a 40 mg L1
dose of KNO3; Group IV was treated with a 40 mg L1 dose of
KNO3+ 0.15 M NaCl.
282 K. Çavuşoğlu et al. Cytologia 82(3)
seedling growth in non-stress conditions. Our results
revealed that the germination percentage, radicle length,
radicle number and fresh weight of the seeds germinated
in the medium with KNO3 alone statistically showed the
same values as the control seeds germinated in distilled
water medium (Table 1). Abdollahi et al. (2010) reported
that 150 mM KNO3 substantially increased the final ger-
mination percentage, radicle length and fresh weight of
Sanguisorba minor Scop., Pimpinella anisum L., Melis-
sa officinalis L. and Nigella sativa L. seeds germinated
under normal conditions. Gharahlar et al. (2012) deter-
minated that 0.5% KNO3 decreased the radicle length
of Eriobotrya japonica Lindle. seeds germinated in
distilled water medium while it increased fresh weight of
the seedlings. In addition, the same researchers observed
that KNO3 application did not have a meaningful effect
on the final germination percentage and radicle number.
Ghobadi et al. (2012) detected that KNO3 (1%) increased
the final germination percentage and radicle length of
Triticum aestivum L. seeds germinated under normal
conditions. Azimi et al. (2015) stated that the final ger-
mination percentage, radicle length and fresh weight of
Glycine max L. and Brassica napus L. seeds germinated
in different concentrations (from 1% up to 4%) of KNO3
increased according to ones of the control seeds germi-
nated in distilled water medium. Golizadeh et al. (2015)
reported that 10.1 mM KNO3 reduced the final germina-
tion percentage and radicle length of Cannabis sativa
L. seeds germinated under normal conditions while it
increased fresh weight of the seedlings. Although some
of these results were consistent with our findings, some
were not consistent with our findings. It can be said that
KNO3 may show different effects on the seed germina-
tion and seedling growth depending on the plant species
and the concentrations used.
In addition, some growth regulators may particularly
cause mitotic irregularities, cell distortions and chromo-
somal aberrations even without stress conditions (Ünal
et al. 2002, Tabur and Demir 2010b). So far, there is no
extant literature data relating to effects of KNO3 on the
mitotic activity and chromosomal aberrations in non-
stress conditions. Therefore, we have investigated firstly
whether KNO3 is affecting these parameters in normal
conditions or not. The data obtained in the present work
indicated that the mitotic index in root meristems of A.
cepa (group III) seeds exposed to KNO3 application in
normal conditions reduced 25% according to ones of
the group I (control) seeds germinated in distilled water
medium. That is, 40 mg L1 KNO3 application showed a
repressive effect on the mitotic activity by slowing down
cell division. Moreover, frequency of chromosomal aber-
rations was increased four-fold with this dose of KNO3
application. In this case, we can say that some aberra-
tions may result from this stimulator (Table 2).
The most striking abnormalities in the present study
were disorderly prophase, the bridge in anaphase and
uncoiling chromosome. Mitotic irregularities, such as
fault polarization and bridge in anaphase and telophase,
may be mainly the result of spindle dysfunction and con-
stitute a significant portion of chromosomal aberrations.
Fig. 2. Normal mitosis phases in root tips meristems of Allium cepa L. root tip cells. Prophase (a), metaphase (b), anaphase (c),
telophase (d). Scale bar =10 µm.
2017 Physiological and Cytogenetical Effects of KNO3 on Salinity 283
Spindle dysfunction may lead to abnormal segregation
of chromosomes due to defective microtubule–kineto-
chore interaction, and abnormal mitotic segregation of
chromosomes triggers bridge formations (Tabur and
Demir 2010b).
Physiological and cytogenetical effects of KNO3 under
saline conditions
It was reported previously that saline conditions nega-
tively affect growth and development events in general,
even in halophytes. However, the effect mechanism of
salinity has not been completely clarified so far (Al-
Karaki 2001, Ghoulam and Fares 2001). It is well known
that salinity prevents seed germination (Chartzoulakis
and Loupassaki 1997, Hosseini et al. 2002, Demir et al.
2003) and seedling growth (Dash and Panda 2001, El-
Mashad and Kamel 2001, Ashraf et al. 2002). The seed-
ling growth and germination of A. cepa seeds, as expect-
ed, were inhibited under saline conditions (Table 1). Salt
stress can perform its preventive effect in many ways.
It may interfere with seed germination by changing the
water status of the seed so that water uptake is inhib-
Fig. 3. Chromosomal aberrations examined in mitotic phases of Allium cepa L. root tip cells. Micronucleus (a), irregular pro-
phase (b), uncoiling chromosome (c), sticky chromosome (d), irregular anaphase (e), bridge in anaphase (f), fault polar-
ization in anaphase (g), vagrant chromosome in anaphase (h), lagging chromosome in anaphase (i), alignment anaphase
(j), fault polar ization in telophase (k), vagrant chromosome in telophase (l). Scale bar =10 µm.
284 K. Çavuşoğlu et al. Cytologia 82(3)
ited (Ali 2000). Our results showing the decrease in the
fresh weight and water content of the seedlings in saline
medium may be explained by the failure of the roots to
receive sufficient water due to the high osmotic pressure
of the medium (Al-Karaki 2001). The inhibitive effect of
salt on the radicle length and radicle number may result
from reducing cell division (McCue and Hanson 1990),
nucleic acid and protein synthesis (Prakash et al. 1988).
On the other hand, KNO3 treatment markedly re-
moved the inhibitor effect of salt stress on the seed
germination and seedling growth parameters such as the
radicle length, radicle number and fresh weight (Table
1). Unfortunately, there are few studies examining ef-
fects of KNO3 on the seed germination and seedling
growth under saline conditions until now. Zheng et al.
(2008) reported that 6 mM KNO3 application signifi-
cantly relieved the negative effect of salt stress on the
radicle length of wheat seeds. Jabeen and Ahmad (2011)
determined that 250 mg L1 KNO3 increased the fresh
weight of Helianthus annuus L. and Carthamus tinctorius
L. seedlings grown under saline conditions. Hamayun
et al. (2014) observed that 5 and 10 mM KNO3 remark-
ably increased the fresh weight of Glycine max L. seed-
lings grown in saline medium. All of these results are
consistent with our findings. That KNO3 alleviates salt
stress on the seed germination and seedling growth can
be understood from the decrease in the salts osmotic
effects. For example, at 0.15 M NaCl medium, KNO3 ap-
plication significantly increasing the fresh weights of the
seedlings compared to the control indicates this prob-
ability (Table 1). Moreover, it reduced the preventive ef-
fect of salt on the seed germination and seedling growth
by stimulating mitotic activity of the embryo (Table 2).
It could have made a counter-attack against the ABA be-
ing a germination inhibitor whose amount probably in-
creases due to the salt existence. In addition to all these,
KNO3 might have been successful in decreasing the in-
hibitive effect of salt stress on the seed germination and
seedling growth by increasing nucleic acid and protein
synthesis, by providing stabilization of cell membranes
or by raising antioxidant enzyme activities (Zheng et al.
2008, Jabeen and Ahmad 2011, Kazemi 2013, Lara et al.
2014).
The cytotoxicity level of a test compound can be
determined based on the increase or decrease in the
mitotic index (MI), which can be used as a parameter of
cytotoxicity in studies of environmental biomonitoring
(Fernandes et al. 2007). The inhibitory and cytotoxic
effects of salt stress on mitotic activity are known for
a long time (Radic et al. 2005, Tabur and Demir 2009,
2010a, 2010b). According to some researchers, high salt
concentration causes total inhibition of mitotic activity
and chromosomal abnormalities in root-tip cells (Radic
et al. 2005). With the present work, it is worth mention-
ing again that salinity adversely affected the mitotic
activity and chromosome behaviors in root meristem
cells of A. cepa. Our data indicated that salinity accord-
ing to the control decreased 50% the mitotic index and
showed higher number of chromosomal abnormalities.
The frequency of aberrations by salinity increased ap-
proximately five times as compared to the control group.
For example, the frequency of chromosomal aberra-
tions in the root tip meristems of the seeds germinated
in distilled water was 11.4 while it was 54.1 at 0.15 M
salinity. Besides, KNO3+NaCl simultaneous application
could be successful in alleviating the negative effect of
salinity on the mitotic activity. In addition, KNO3+NaCl
simultaneous application showed marked achievement
in decreasing of the detrimental effect of salinity on the
chromosomal aberrations as compared to KNO3 alone.
That is, frequency of chromosomal aberrations was de-
creased 36% by the simultaneous application (Table 2).
These results indicated the repair role of KNO3 against
salt injuries during A. cepa mitosis.
In general, accurate chromosome segregation in mi-
tosis requires that sister kinetochores attach to microtu-
bules emanating from opposite spindle poles. Because
kinetochore attachment is a stochastic process, it is er-
ror prone and can result in chromosome malorientation
(Rieder and Salmon 1998). Mitotic irregularities such
as disorderly prophase and anaphase, fault polariza-
tion, alignment anaphase, vagrant chromosomes and
bridges may be mainly the result from mentioned rea-
sons or spindle dysfunction and constitute a significant
portion of chromosomal aberrations. The formations
of micronucleus are likely the consequence of vagrant
chromosomes and fragments (Briand and Kapoor 1989).
The lagging chromosomes are presumably the result
of a weak mitotic effect. NaCl may lead to the highest
number of laggards. According to Fiskesjö (1997), NaCl
caused c-mitotic effects including lagging chromosomes.
Sticky chromosomes may result from improper folding
of the chromatin fibres (Klasterska et al. 1976). Some
researchers reported that the stickiness reflects highly
toxic effect on chromatin (Fiskesjö and Levan 1993).
The prophase and metaphase cells with uncoiled chro-
mosomes may be the result of disorderly chromosome
contractions. Also, anaphase and telophase bridges could
be the result of inversions (Tabur and Demir 2010b). In
short, KNO3 might function as a stimulator preventing
the synthesis of protein necessary for the normal cell di-
vision and slowing down mitotic cycle.
There is nearly no present literature data related to
effects of KNO3 application in saline conditions on the
physiological and cytogenetical parameters studied here.
Therefore, our results in the present work have reported
for the first time particularly in saline conditions. Conse-
quently, our study indicates that KNO3 may significantly
improve the activations such as the seed germination,
seedling growth and mitotic activity in saline conditions.
However, the mechanisms by which salinity inhibits
growth are complex and controversial. Moreover, they
2017 Physiological and Cytogenetical Effects of KNO3 on Salinity 285
may vary according to species and cultivar. A universal
mechanism has not been established yet. Although the
causes of salinity have been characterized, our under-
standing of the mechanisms by which salinity prevents
plant growth is still rather poor. Therefore, further stud-
ies should be carried out in order to gain more knowl-
edge about effect of KNO3 on molecular metabolism of
germination, cell division and cell cycle. This work may
serve to provide new conceptual tools for designing hy-
potheses of salt tolerance in plants.
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