Advances in Environmental Biology

Advances in Environmental Biology, 8(17) September 2014, Pages: 1082-1087
AENSI Journals
Advances in Environmental Biology
ISSN-1995-0756
EISSN-1998-1066
Journal home page: http://www.aensiweb.com/AEB/
The Effect of Salinity and Drought Stress on Seed Germination, Seedling Growth
and Biochemical Changes in Borago
Mahboubeh Ahmadi and Mehrab Yadegari
Department of Agronomy and Medicinal Plants, Faculty of Agriculture, Islamic Azad University, Shahrekord Branch, Shahrekord, Iran
ARTICLE INFO
Article history:
Received 25 September 2014
Received in revised form
26 October 2014
Accepted 25 November 2014
Available online 29 December 2014
Keywords:
Borago officinalis L.,
Environmental stress,
Growth
ABSTRACT
Seed germination is one of the sensitive stages in plant growth, and reduces the
germination indexes and the seedling growth. In order to investigate the effect of
drought and salinity stress on germination seedling and studying proline changes in
borage seedling in the condition of drought stress (0, -0.2, -0.4, -0.6, -0.8 and -1 MPa)
and salinity (0, -0.2, -0.4, -0.6 and -0.8 MPa) two experiments was completely
conducted in a randomized design with three replication. Results showed that drought
and salinity stress were significantly effective on germination percentage, germination
rate, mean time to germination, normal seedling percentage, rootled length, shoot
length, seed vigor, seedling dry weight, the duration of reaching to 5 (D05), 10 (D10)
and 20 (D20) percentage of germination, and content of proline. Salinity and drought
stresses were significantly reduced in seed germination percentage, germination rate,
normal seedling percentage, rootled length, shoot length, seed vigor, seedling dry
weight and the increase in the duration in reaching to 5 (D05), 10 (D10) and 20 (D20)
and content of proline. The highest germination percent with the average of 77 percent
was related to control condition, but with the increase in the salinity levels to -0.8 MPa
and drought stress to -1 MPa germination percentage was 20 percentage. On the whole,
the highest amount of other measured indexes were related to control condition (nonstress).
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Mahboubeh Ahmadi and Mehrab Yadegari., The Effect of Salinity and Drought Stress on Seed Germination, Seedling
Growth and Biochemical Changes in Borago. Adv. Environ. Biol., 8(17), 1082-1087, 2014
INTRODUCTION
Environmental stresses, especially drought and salinity stress are important factors that result in a
remarkable reduction in germination, growth and the appropriate establishment of plants in all over the world.
The reduction of fertilizable fields, increase in demanding for crop products and also the increase in
consumption of crop products, especially medical plants, for curing the disease and providing the society’s
health and survival are factors that are considered important in a stable development in agricultural portion
[33,40]. Initial stages in plant growth, especially seeds germination, is one of the most sensitive growth stage
that is considerably affected by stress and in other words germination and seedling initial growth stages are
critical stages for establishing plant in salinity stress condition [34]. Survival and plants growth evaluation in
this stage can be somehow the indicator of the amount of tolerance of stress. The ability of seed for accessing to
water is decreased by the reduction of osmotic potential and matric and can cause the disorder in seed
germination [12,39]. Seeds of genotypes that in germination and seedling stages have higher moisturizing stress
tolerance also have this ability in subsequent stages. Increase in levels of drought stress can cause reduction in
the uniformity of germination [41]. Different reports showed that low potential of water in the environment is
the main factor in limiting the germination [8, 9]. Several studies showed that germination and seedling growth
will be decreased in effect of different lifeless stresses like salinity, drought and cold weather [1,2, 4, 5,6, 15, 18,
23,42,43,44]. Drought stress can increase the uniformity and the time of germination onset [14, 32, 41].
Generally, with the increase of drought stress, the ability of suction of water by seeds will be decreased and the
necessary duration for water sucking will be increased and consequently the start of germination processes will
be postponed and in addition there will a disorder in it and the time will be increased until the start of
germination [12].
The plants in environmental stress like drought, salinity, heat, etc. with stocking the osmotic adjusting
material will defeat the stress [5]. Proline is a soluble acid amine in water that will be increased in the
Corresponding Author: Mehrab Yadegari, Department of Agronomy and Medicinal Plants, Faculty of Agriculture, Islamic
Azad University, Shahrekord Branch, Shahrekord, Iran.
Tel: +98 9133814318 Fax: +98 3813361093
E-mail: [email protected]
1083
Mahboubeh Ahmadi and Mehrab Yadegari, 2014
Advances in Environmental Biology, 8(17) September 2014, Pages: 1082-1087
environmental stresses and the increase in its amount is the indicator of plant resistance in opposes to stress
condition. Proline will protect the protein and cell membrane from intense density damage of Ione [25]. The
resistible genotype indicated more and quicker reaction in terms of proline concentration to sensitive Alfalfa
species [27]. Proline concentration in the time of drought stress in other plants like alfalfa [19], corn [28] and
peanut [31] is also reported.
Borage with its scientific name Borago officinalis L. is a biennial or perennial belongs to the species of
Boraginaceae. This species is one of the valuable medical plants that grow wildly in north districts of Iran and
Qazvin province. Knowing the importance of that borage is a medical plant and its increasing process of
consumption in traditional medicine and by knowing the damage that is resulted from intensive beneficiary of
this wild plant in the Flore of Iran, the necessity of sowing this plant in a large amount and commercially is
considered. For most of the medical plants such as borage, the mechanisms of resistance to stresses are not
investigated. Hence, the aim of this study is to examine the effects of drought and salinity stress on the indexes
of germination, growth and changes in the amount of proline.
MATERIAL AND METHODS
In order to examine the effect of drought and salinity stress on germination indexes and changes of proline
amount in borage, two experiments complete randomized design with 3 replication in laboratory of Islamic
Azad University branch of Ahwaz in 2013 were conducted.
The drought stress experiment was conducted in 6 levels with osmotic pressure 0, -0.2, -0.4, -0.6, -0.8 and 1 MPa(Michael Coffman method) and with using PEG (Poly Ethylene Glycol 6000) on Borago seeds.The
salinity stress experiment was conducted in 5 levels with osmotic pressure 0, -0.2, -0.4, -0.6 and -0.8 MPa and
by using NaCl on seeds of Borago.
The seeds at first, sterilized with hypo chloride sodium %3 in 2 minutes and then will be washed 3 times
superficially with distilled water and 50 seeds will be transferred to glass Petri dish with 12 cm diameter and for
the duration of the experiment 5ml solution with different levels was added to each Petri dish and for 14 days
were transferred to a 20±1 ºC temperature with darkness condition and the number of geminated seeds in each
day was counted and recorded.
After the termination of germination term, below indexes were measured in both drought and salinity
conditions: germination rate, germination percentage, mean time to germination, normal seedling percentage,
duration to 5 (D05), 10 (D10), 20 (D20) percent germination rootled and shoot length, the seed vigor and the dry
weight of seedling was measured, and in a larger amount were sowed in tray proline index was conducted based
on Bates et al methods [7].
All data were subjected to ANOVA using the statistical computer package SAS and treatment means
separated using Duncan‘s multiple range test at P<0.05 level.
Results:
The effect of drought stress on germination indexes:
The results of variance analysis showed that the effect of drought stress on germination, germination rate,
time to germination, rootlet and shoot length, normal seedling percentage, duration to 5 (D05), 10 (D10), 20
(D20) percent germination rootled and shoot length, the seed vigor and seedling dry weight and proline in
probable %1 level were significant (table 1). Similar results were obtained by other researchers that in all of
them indexes of germination were significantly affected by different levels of drought stress [10, 11,29].
Table 1: Analysis of Variance of different levels of drought stress on Borage seed germination indexes.
S.O.V
df
GP
GR
MTG
NSP
SL
RL
SVI
SDW
T05
T10
T20
Prolin
Drought
5
1522/13**
47/5**
4/33**
2072/35**
12/52**
32**
581663/2**
0/00001**
9187/43**
12382/4**
24695/33**
0/56**
Error
12
7/11
0/18
0/19
24381
0/13
0/2
1176/32
0/0000001
64/61
50/66
317/11
0/009
C.V %
5/47
7/38
6/37
7/57
12/93
7/3
6/88
7/41
11/84
7/96
12
7/64
**significant at 1% probability level. Gp: germination percentage. GR: germination rate. MTG: mean time of germination. NSP: normal seedling percentage. Sl: rootled length. Rl: shoot
length. SVI: seed vigor. SDW: dry weight of seedling. T05: duration to 5 percent germination. T10: duration to the start of germination. T20: duration to 20 percent germination.
The results of mean comparisons of the effect of different levels of drought stress on seed germination
indexes showed that with the increase in different levels of drought stress, germination indexes such as
germination percentage, germination rate, normal seedling percentage, rootled length, shoot length, the seed
vigor and the dry weight of seedling were significantly reduced and mean time to germination, duration to 5
(D05), 10 (D10) and 20 (D20) percentage of germination and content of proline were significantly increased
(table 2).
The highest seed germination percentage with the means of 77.3 % in the control condition and the lowest
seed germination percentage with the mean of 20.67 % in the drought stress condition -1 MPa was observed
(table 2). The highest germination rate with the mean of 11.08 in day was related to the control condition (table
2). The highest normal seedling percentage with 71.33 and 70.67 %, rootled length with the mean of 5.03 and
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Mahboubeh Ahmadi and Mehrab Yadegari, 2014
Advances in Environmental Biology, 8(17) September 2014, Pages: 1082-1087
4.97 cm, shoot length with the mean of 9.1 and 9.33 cm, seed vigor with the mean of 1007.47 and 1010.87 and
seedling dry weight with the mean of 0.0065 gr were respectively related to control and -2bar stress condition
(table 2).
The lowest mean time to germination, the period of reaching to 5, 10 and 20 percent of germination and
content of proline were respectively with the means of 5.57, 15, 36 and 27.67 hr. and 0.77 were observed in
control condition (table 2). With the increase in levels of drought stress, seed accessing to water was reduced
and the activity of the enzymes which are responsible for changing in germination also diminished. In this way
it is possible that the germination percentage will be reduced [3].
The reduction of seed germination under the effect of drought stress results in the reduction of cell moisture
and its effects on protein construction and hormones release and generally because of the reduction of the
potential of the water of the developing cells, germination percentage and rate most of the plants in the
moisturizing stress condition will be reduced [20]. Drought stress resulted in the reduction in germination
indexes of seeds of Cucurbita pepo L. Nigella sativa L. and Borago officinalis L [10]. The cause of germination
rate and the creation of abnormal seedling is the lack of enough energy for starting the related process of
germination [21]. Maybe the reduction in the normal seedling percentage is because of water shortage in an
intensive stress condition that in which the seedling has not the ability to grow normally. The reduction in the
normal seedling percentage under the condition of stress was reported [2, 3].It is reported about medical plants
that with the increase of drought stress radicle length was significantly reduced [11,24].
With the reduction of water potential rootled and soot length was significantly reduced. It is reported that
one of the factors in reduction of the rootled length in stress condition is the reduction or the lack of
transforming the nutrition from cotyledon to embryo. In addition, the reduction of sucking water by the seed in
stress condition will cause in the reduction of hormone release and enzymes activity and consequently will
cause a disorder in seedling growth [16].The cause of the reduction in seedling growth and subsequently the
reduction in seedling dry weight can be related by the reduction in seed reserve utilization to seedling and
seedling growth and also mentioned that with the increase in levels of stress [2]. The activity of antioxidant
enzymes is increased that the change in the activity of these enzymes is the cause of the increase of damage in
stress condition that can be effective on growth and seedling dry weight. The period for reaching to 10 percent
germination is the indicator of the time for the beginning of germination. With the increase in the stress
intensively, the periods for reaching to 10, 50 and 90 percent of germination were significantly increased [24,
29, 32,33]. Drought stress have significant effects on the amount of proline of shoot and the root of dill [17].
Table 2: Mean comparison of the effects of different levels of drought stress on seeds of Borage.
Drought
GP
GR
MTG
NSP
SL
SL
SVI
SDW
T05
T10
T20
Prolin
Mpa
0
77.33a
11.08a
5.57f
71.33a
5.03a
9.1a
1007.47a
0.0065a
15f
36f
72.67f
0.77f
-0.2
70.67b
8.95b
6.39de
70.67a
4.97a
9.33a
1010.87a
0.0065a
27e
42e
69.33e
0.84e
-0.4
52c
7.35c
6.03e
49.33b
3.73b
7.9b
572.93b
0.0052b
26.67d
40d
96d
1.1d
-0.6
42.67d
3.82d
6.84c
39.33c
1.6c
5.73c
289.73c
0.0034c
74.33c
86c
128c
1.3c
-0.8
28.67e
1.97e
8.33b
22.67d
1.03d
3.37d
99.33d
0.0025d
111b
140b
252b
1.57b
-1
20.67f
1.29f
8.45a
5.33e
0.4e
1.3e
9.2e
0.0003e
153a
192a
272a
1.9a
Gp: germination percentage. GR: germination rate. MTG: mean time of germination. NSP: normal seedling percentage. Sl: shoot length. Rl:
radicle length. SVI: seed vigor. SDW: dry weight of seedling. T05: duration to 5 percent germination. T10: duration to the start of
germination. T20: duration to 20 percent germination.
The effect of salinity stress on germination indexes:
We saw significant differences on seeds of Borago of germination indexes such as germination percentage,
germination rate, mean time to germination, rootled and shoot length, normal seedling percentage, the duration
to 5 (T05), 10 (D10) and 20 (D20) percent germination, seed vigor, seedling dry weight and proline were
significant in 1% probable level (table 3). In different plants also reported that salinity stress has a significant
effects on germination indexes that is similar to the results of this experiment [5, 15, 22].
Table 3: Analysis of Variance of the effects of levels of salinity stress on seeds of Borago.
S.O.V
df
GP
GR
MTG
NSP
SL
RL
SVI
SDW
T05
T10
T20
Prolin
Salinity
4
1840.4**
59.91**
13.77**
2400.26**
9.69**
36.34**
569132.45**
0.00001**
20365.56**
34299.6**
35706.01** 0.22**
Error
10
8.53
0.34
0.31
41803
0.18
0.13
1492.31
0.0000001
650.26
243.2
235.81
0.006
C.V %
5.95
10.23
7.39
6.06
15.26
6.59
8.51
12
22.38
13.35
9.32
11.1
**significant at 1% probability level. Gp: germination percentage. GR: germination rate. MTG: mean time of germination. NSP: normal seedling percentage. Sl: shoot length. Rl: rootled
length. SVI: seed vigor. SDW: dry weight of seedling. T05: duration to 5 percent germination. T10: duration to the start of germination. T20: duration to 20 percent germination.
Mean comparisons of the effects of salinity stress on borago seed germination indexes showed that the
highest percentage of germination with the means of 77.33 % is related to control condition and with the
increase of salinity stress to -0.8 MPa the percentage of germination decreased to 20.67 (table 4). The highest
normal seedling percentage, rootled and shoot length, seed vigor and seedling dry weight is respectively with
means of 71.33%, 5.03 cm, 9.1cm, 1007.47 and 0.0065 gr were related to the control condition and with the
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Mahboubeh Ahmadi and Mehrab Yadegari, 2014
Advances in Environmental Biology, 8(17) September 2014, Pages: 1082-1087
increase in salinity stress levels to -0.8 MPa (table 4). The highest mean time to germination with the mean of
10.88 and the highest period for reaching 5,10 and 20 percent of germination respectively with the means of
206, 292 and 328 hr. was related to -0.8 MPa salinity stress (table 4). The amount of proline will be significantly
increased with the increase of the salinity stress levels, so that the proline in control condition reached from 0.52
ml in fresh tissue under the salinity stress condition of -0.8 MPa (table 4).
Salinity stress can cause reduction in the activity of involved enzymes germination by lowering the water
potential and by doing this can cause the reduction of germination percentage. Salinity stress have an influence
on seed germination via osmotic effects and ion toxicity [13]. Different levels of salinity stress has a significant
effects on germination component and with the increase in salinity the amount of germination indexes were
reduced. Maybe the reason of the reduction in the germination rate in levels upper the salinity stress, the
reduction in water potential and consequently reduction in the rate of sucking water and the toxic effect of
sodium ion was obtained [41]. The reduction in germination indexes under the effects of salinity stress is
attributed to the reduction in the amount of initial sucking of water and also the negative influence of low
osmotic potential and the toxicity of ions on biochemical process of catabolic and anabolic phases [30]. The
reduction in normal seedling percentage with the increase of salinity stress levels attributed by the toxic effects
of ions that influenced the normal seedling growth and in this way, reduction in normal seedling percentage,
seedling length, dry weight and seed vigor was made. Decrease in normal seedling percentage, seedling length
dry weight and seed vigor made by the increase of salinity concentration levels were reported by other
scientists[3, 5, 15, 26, 36,37]. The duration of 10% germination is known as the time to the start of germination
and with the increase in stress levels, the time of germination beginning has been increased and this increase in
the time to the starting of germination can be related of the reduction in germination rate and water sucking.
Generally with the increase of salinity stress the ability of sucking water by the seeds will be reduced and the
needed period for sucking water will be increased, and consequently the beginning of germination process will
be postponed and also there will be a disorder in it [12].
The increase of proline amount in drought and salinity stress reduced the stress damage. Hence, in order to
reduce the amount of damage, the plant increases proline production in the conditions of the high stress levels.
Proline has the assimilation role as the source of carbon and nitrogen. Also proline has the responsibility of
protecting the plant against free radicals damages [35]. With the osmotic tension entrance to the plant and the
disordering the osmotic balance, for surviving and osmotic balancing in stress condition the plant will resist
against the stress by increasing its proline amount and sugar as a kind of mechanism [38].
The content of proline increase with the increases of salinity stress and this is one of the biochemical
mechanisms in reaction to stress. Inside the plant cell the proline will perform as a substantial for preserving the
balance of osmoses between cytoplasm and vacuole [40].
Table 4: Mean comparisons of the effects of different levels of salinity stress on germination indexes of seeds of borago.
Salinity
GP
GR
MTG
NSP
SL
SL
SVI
SDW
T05
T10
T20
Mpa
0
77.33a
11.08a
5.57e
71.33a
5.03a
9.1a
1007.47a
0.0065a
15e
36e
72.67e
b
b
d
b
b
b
b
b
d
-0.2
71.33
9.64
6.41
65.33
3.93
8.27
797.73
0.0042
16.67
38de
84.8d
-0.4
45.33c
5.03c
6.27cd
39.33c
3.24c
5.77c
354.1c
0.00277c
39c
76c
114c
d
d
b
d
d
d
d
d
b
b
-0.6
30.67
2.08
8.23
24.67
1.36
2.8
102.74
0.0012
117
142
224b
-0.8
20.67e
1.03e
10.88a
3.33e
0.7e
0.97e
5.67e
0.0004e
206a
292a
328a
Gp: germination percentage. GR: germination rate. MTG: mean time of germination. NSP: normal seedling percentage. SL: shoot length.
RL: rootled length. SVI: seed vigor. SDW: dry weight of seedling. T05: duration to 5 percent germination. T10: duration to the start of
germination. T20: duration to 20 percent germination.
Conclusion:
Our results showed that the drought and salinity stress were the cause of reduction in germination
percentage, germination rate, normal seedling percentage, rootled and shoot length, seed vigor and seedling dry
weight, and increase in the reaching to 5 (D05), 10 (D10) and 20 (D20) percent germination, content of proline
and the mean time of germination. The reduction in germination indexes can be attributed to the increase of
proline amount in the condition of high levels of drought and salinity stress. The seed vigor index is related to
the normal seedling percentage and seedling length and the reason of the reduction in seed vigor related of the
reduction in rootled, shoot length and seedling percentage under high stress level condition. The reduction in
seedling growth also was cause of reduction in seedling dry weight. The produced seedling under the drought
and salinity stress condition increased proline amount in order to prevent from the intensive damage which can
be a defensive mechanism against stress condition.
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