Evaluation of Drought Stress on Relative Water Content and Chlorophyll Content of Sesame (Sesamum indicum L.) Genotypes at Early Flowering Stage
In order to evaluate drought stress on relative water
content (RWC) and chlorophyll content of 27 Sesame genotypes, a factorial
experiment based on randomized complete block design with three replications
was conducted in 2006 in Moghan region, Iran. Factors were 27 Sesame genotypes
(Karaj 1, Yekta, Oltan, Moghan 17, Naz takshakheh, Naz chandshakheh, Borazjan
2, Borazjan 5, Darab 14, Varamin 37, Varamin 237, Varamin 2822, Zoodrass
IS, Hendi, Chini, Yellow white, 5089, Panama, Do-1, TF-3 , TKG-21, J-I,
RT-54, Hendi 9, Hendi 12, Hendi 14 and Jiroft) and irrigation levels (full
irrigation and irrigation until flowering stage). Results showed that
Varamin 2822 and Varamin 237 genotypes had the highest RWC of 84.100 and
81.217%, respectively. The most chlorophyll a content was observed in
Hendi 9 genotype of 106.237, the most chlorophyll b in Karaj 1 genotype
of 84.665 and the most chlorophyll total in Hendi genotype of 182.395
mg g-1 leaf fresh weight. It seems that Varamin 2822 genotype
having the highest RWC and Hendi 9 and Hendi genotypes having the most
chlorophyll a and chlorophyll total, respectively, are recommended for
planting in arid and semi-arid conditions.
to cite this article:
M. Hassanzadeh, A. Ebadi, M. Panahyan-e-Kivi, A.G. Eshghi, Sh. Jamaati-e-Somarin, M. Saeidi and R. Zabihi-e-Mahmoodabad, 2009. Evaluation of Drought Stress on Relative Water Content and Chlorophyll Content of Sesame (Sesamum indicum L.) Genotypes at Early Flowering Stage. Research Journal of Environmental Sciences, 3: 345-350.
Chlorophyll content is one of the major factors affecting photosynthetic capacity.
Reduction or no-change in chlorophyll content of plant under drought stress
has been observed in different plant species and its intensity depends on stress
rate and duration (Rensburg and Kruger, 1994; Kyparissis
et al., 1995; Jagtap et al., 1998).
Chlorophyll content in plant is considered as a favorite aspect for plant growth
(Farquhar and Richards, 1984). Chlorophyll content of
leaf is indicator of photosynthetic capability of plant tissues (Nageswara
et al., 2001; Wright et al., 1994).
Flooding irrigation about 1 cm above soil surface led to senescence and decrease
in chlorophyll content of leaves. In this study, severe drought stress resulted
in increase in chlorophyll content and then, remained constant (Mensah
et al., 2006). De-Souza et al. (1997)
reported that soybean plants grown at the greenhouse and were subjected to drought
stress from early seed filling stage to maturity stage, rapidly lost their leaf
chlorophyll content than control plants.Schlemmer et al.
(2005) stated that drought stress had no significant effect on chlorophyll
content of maize leaf and concluded that decrease in turger pressure caused
by water deficit, resulted in change in amount of far red radiation passed through
the leaf and this reason, read of chlorophyll meter device was changed. In other
words, light reflection from leaf was increased with increasing drought stress.
Barry et al. (1992) reported chlorophyll destruction
in barley as affected by water deficit. Xian-He et al.
(1995) stated the same results in wheat. Also, Fotovat
et al. (2007) found that by exerting severe drought stress on wheat,
chlorophyll content of leaf significantly decreased.
In mid 80s, RWC was introduced as a best criterion for plant water status which,
afterwards was used instead of plant water potential as RWC referring to its
relation with cell volume, accurately can indicate the balance between absorbed
water by plant and consumed through transpiration. Schonfeld
et al. (1988) showed that wheat cultivars having high RWC, are more
resistant against drought stress. Generally, it seems that osmoregulation is
one of the main mechanisms preserving turger pressure in most plant species
against water loss from plant so, it causes plant to continue water absorption
and retain metabolic activities (Gunasekera and Berkowitz,
1992). Zlatko Stoyanov (2005) found that by exerting
drought stress for 14 days and reaching soil water potential to -0.9 MPa, osmotic
potential and turger pressure in first leaf of bean strongly was decreased.
Ramos et al. (2003) stated that RWC of bean leaves
under drought stress significantly was lesser than control. Lazacano-Ferrat
and Lovat (1999) subjected bean plant to drought stress and after 10, 14
and 18 days after irrigation was withholded, they evaluated RWC of stem and
found that RWC was significantly lower comparing with control plants. Gaballah
et al. (2007) applied antitranspirant maters on two Sesame cultivars
named Gize 32 and Shanavil 3 and observed that this matters by preventing water
transpiration from leaves, led to in crease in RWC in these cultivars.
The objective of this research was to determine RWC and chlorophyll content
of Sesame leaves under drought stress in Moghan region, Iran.
MATERIALS AND METHODS
In order to evaluate drought stress on relative water content (RWC) and
chlorophyll content of 27 Sesame genotypes, a factorial experiment based
on randomized complete block design with three replications was conducted
in 2006 in Moghan region, Iran. Factors were 27 Sesame genotypes (Karaj
1, Yekta, Oltan, Moghan 17, Naz takshakheh, Naz chandshakheh, Borazjan
2, Borazjan 5, Darab 14, Varamin 37, Varamin 237, Varamin 2822, Zoodrass
IS, Hendi, Chini, Yellow white, 5089, Panama, Do-1, TF-3, TKG-21, J-I,
RT-54, Hendi 9, Hendi 12, Hendi 14 and Jiroft) and irrigation levels (full
irrigation and irrigation until flowering stage). In order to calculate
leaf chlorophyll content, 1 g punched fresh leaf sample was grinded along
with 40 mL acetone 80% (v/v) until it was well smoothed.
Resulted green liquid was transferred through Whatman paper No. 2. Eventually,
final liquid volume using acetone 80% reached to 100 mL. Thereafter, chlorophyll
extract light densities were read using Spectrophotometer at 645, 663 and 652
mn wavelengths. Chlorophyll a, b and total as mg g-1 leaf fresh weight
were calculated according to Dhopte and Manuel (2002):
Mg chlorophyll a = [12.7(D663) -
2.69 (D645)]xV/1000 w
Mg chlorophyll b = [22.9(D645) -
Mg chlorophyll total = [20.2(D645)
+ 8.02(D663)]xV/1000 w
where, D is the chlorophyll extract light density, V is final volume of chlorophyll
extract in acetone 80% and w is leaf fresh weight as gram. Also, in order to
calculate RWC, leaf fresh weight samples were weighed, then were submerged in
distilled water and finally were dried at 70 °C for 48 h and were weighed
again. RWC was calculated according to Dhopte and Manuel (2002):
where, FW is fresh weight, DW is dry weight and TW is turger weight of
RESULTS AND DISCUSSION
Change of Leaf Chlorophyll
Effects of irrigation was significant (p<0.01) on leaf chlorophyll
content. Chlorophyll a content significantly was higher (Table
1) in irrigation treatment than stress. Its value in irrigation and
stress conditions was 80.039 and 77.239 mg g-1 leaf fresh weigh.
Based on the results, it was revealed that genotypes with lowest yields,
had the highest chlorophyll a content so that, Hendi 9 genotype which
is classified in low yielding genotypes, significantly had the highest
chlorophyll a. Chlorophyll b content under irrigation and stress treatments
was obtained of 74.626 and 85.862 mg g-1 leaf fresh weight.
The highest chlorophyll b was belonged to Karaj 1 genotype of 100.513
mg g-1 leaf fresh weight. Unlike the chlorophyll a, it is clear
that the genotypes with the lowest yields had the lowest chlorophyll b
contents. Also, chlorophyll total like the chlorophyll b content, significantly
was higher (p<0.01) in irrigation treatment than stress. The highest
chlorophyll total was observed in Hendi genotype of 182.395 mg g-1
leaf fresh weight.
|| Mean comparisons of main effects of genotypes and irrigation
levels on measured traits
|Numbers with the same letters, have no significant difference
to each other
Results showed that the genotypes with the lowest yield had the lowest chlorophyll
total and vice versa. Water deficit can destroy the chlorophyll and prevent
making it (Lessani and Mojtahedi, 2002). Also, some researchers
have reported damages to leaf pigments as a result of water deficit (Montagu
and Woo, 1999; Nilsen and Orcutt, 1996). Mensah
et al. (2006) found that subjecting Sesame to drought stress caused
leaf chlorophyll was increased and then remained unchanged.
Beeflink et al. (1985) reported increase in chlorophyll in onion
under drought stress. Mentioned results are in accordance with this results
confirming increase in chlorophyll b and total under drought stress. Ramalho
et al. (2000) stated that ratio of chlorophyll a/b in late summer
is less than spring of 2.6 units which may be attributed to more precipitations
in spring. A reason for decrease in chlorophyll content as affected by water
deficit is that drought or heat stress by producing reactive oxygen species
(ROS) such as O2¯ and H2O2, can lead to
lipid peroxidation and consequently, chlorophyll destruction (Mirnoff,
1993; Foyer et al., 1994). Also, with decreasing
chlorophyll content due to the changing green color of the leaf into yellow,
the reflectance of the incident radiation is increased (Schlemmer
et al., 2005). It seems that this mechanism can protect photosynthetic
system against stress. According to the Lawlor and Cornic
(2002) reduction of carbon assimilation confronting water deficit, is due
to limitation of Rubisco synthesis and ATP storage. Studies done as in vivo,
showed that water deficit resulted in destruction of D1 protein of photosystem
2 (Xian-He et al., 1995) but the reason have not
been known, yet.
Change of Relative Water ContentMensah
Irrigation and genotypes significantly (p<0.01) affected RWC (Table
1). In full irrigation, RWC was 81.69% and in stress, it was 73.90%. Moghan
17, Darab 14 and Varamin 237 genotypes had the highest values of 86.56, 88.45
and 88.48%, respectively. Hendi 12 genotype had the lowest RWC of 68.02%.
Mensah et al. (2006) reported that with decreasing irrigation, RWC
in Sesame decreased from 79.8 to 66.5%. Leaf RWC is of the best growth/biochemical
indices revealing the stress intensity (Alizadeh, 2002).
The rate of RWC in plants with high resistance against drought is higher than
others. In other words, plant having higher yields under drought stress should
have high RWC. So, based on the results, mentioned genotypes which are classified
as high and medium yielding genotypes, should be of high-content RWC. Decrease
in RWC in plants under drought stress may depend on plant vigor reduction and
have been observed in many plants (Liu et al., 2002).
Under water deficit, cell membrane subjects to changes such as increase in penetrability
and decrease in sustainability (Blokhina et al., 2003).
Microscopic investigations of dehydrated cells, revealed damages including cleavage
in the membrane and sedimentation of cytoplasm content (Blackman
et al., 1995). Probably, in these conditions, ability to osmotic
adjustment is reduced (Meyer and Boyer, 1981). It seems
that concentration of appropriate solutes to preserve membrane is not sufficient
in this case.
Relations Between RWC and Chlorophyll Content
As shown in Table 2, RWC had the positive and significant
correlations with chlorophyll b and total but non-significant and negative
correlation with chlorophyll a. Also chlorophyll a had the negative and
significant correlation with chlorophyll b and had non-significant correlation
with chlorophyll total. In addition, chlorophyll b had non-significant
correlation with chlorophyll total, as well.
|| Correlations between measured traits
|ns, * and ** are non significant, significant at p<0.01
and significant at p<0.05, respectively
As shown, drought stress making mechanisms inside the plant, leads to
decrease in chlorophyll a but increase in chlorophyll b and total. Also
leaf RWC was decreased as affected by drought. The highest chlorophyll
a, b and total was belonged to Hendi 9, Karaj 1 and Hendi genotypes, respectively
which two latter ones were of high and medium yielding genotypes. So,
this indicates that Sesame genotypes with high yields include high chlorophyll
b and total under drought conditions. Moreover, Moghan 17, Darab 14 and
Varamin 237 genotypes which were among the high and medium yielding genotypes,
had the highest RWC. So, mentioned genotypes (because of retaining chlorophyll
and RWC against drought along with the high yields) in order to planting
as dry-farming, are recommended.
This study was supported by the Central Laboratory of Agricultural Faculty,
University of Mohaghegh Ardabili. Valuable experimental support by Aziz
Jamaati-e-Somarin and Assad Gholizadeh is greatly appreciated. This study
was extracted from M.Sc. Thesis of Mohammad Hassanzadeh.
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