3.2. Expression levels of genes involved in LHCI and LHCII in
response to drought stress.
Six genes which are responsible for coding pigment binding proteins were
studied to find out different transcriptional responses to different
level of drought Stress in two synthetic genotypes (SD-28 and SD-32) and
two conventional wheat genotypes (Chirya-1 and Opata). As shown by
semi-quantitative RT–PCR, that the expression pattern was different
among the studied genes in response to different level of drought
stress, and different level of genes expression was observed. However it
is observed that expression of each genes were related to drought stress
condition and the genotypes.
The expression level of genes which are encoding proteins for LHCI,
namely TaLhca1, TaLhca2 and TaLhca3, showed different
level of expression in SD-28 genotype as shown in (Fig 5). TheTaLhca1 gene show down regulation in drought stress condition
while TaLhca2 gene show up regulation, similarly TaLhca3are down regulated in 80% FC but in severe drought stress condition
show high level of expression. Similarly the genes which are involved in
LHCII namely, TaLhcb1, TaLhcb4 and TaLhcb6 also show
distinct level of expression as shown in (Fig 6). The TaLhcb1show down regulation under drought stress condition and expression level
was decreased as the drought level was increased. The TaLhcb4show up regulation in both drought stress level 80% FC and 60%
capacity while the expression of TaLhcb6 show down regulation
under 80 FC but the expression was induced in severe drought stress
condition 60% FC.
The expression level of genes involved in LHCI, in genotype SD-32 were
not affected by drought stress condition as shown in (Fig 7). TheTaLhca1 genes slightly affected by drought stress and show low
level of expression as compare to control condition, while the
Expression level of TaLhca2 showed up regulation under 80% and
60% FC. Similarly TaLhca3 gene was also not affected by
drought stress and show up regulation. The expression level of genes
which are responsible for LHCII show similar expression pattern with
those involved in LHCI as shown in (Fig 8). The expression level ofTaLhcb1, TaLhcb4, and TaLhcb6 was not affected by drought
stress and showed up expression.
The expression level of genes which are responsible encoding proteins
for LHCI in drought sensitive wheat genotype Opata showed distinct level
of expression as shown in (Fig 9). The TaLhca1 genes were down
regulated and expressions level decreased slowly as drought condition
were increased. Similarly TaLhca2 gene expression was not significantly
affected by drought stress condition, whileTaLhca3 did not
decrease significantly and still remained high at severe drought stress
condition under 60% FC. The expression level of genes which are
responsible for LHCII also showed different level of expression as shown
in (Fig 10). TaLhcb1 genes show down regulation under drought
stress condition while Talhcb4 genes were highly sensitive to
severe drought stress condition but not affected under 80% FC. TheTaLhcb6 gene also shows up regulation and not affected by drought
stress condition. The results indicate that Opata genotype is drought
sensitive as compare to synthetic derivatives SD-28.
The expression level of genes which encode proteins for pigment binding
molecule LHCI showed highly significant results in Stay-Green Chirya-1
genotype as shown in (Fig 11). All the genes which involved in LHCI,
namely The TaLhca1, TaLhca2 and TaLhca3 show higher level of expression
and their expression is not effected by drought stress condition.
Similarly the genes which involve in LHCII, namely TaLhcb1, TaLhcb4 and
TaLhcb6 also show similar results like those which involved in LHCI as
shown in (Fig 12). The expression levels of these genes were not
significantly affected by drought stress condition which is and evident
that Stay-Green Chirya-1 genotype is drought resistant as compared to
Opata and Synthetic derivatives genotypes. The studied morphological
parameters are also evident that Chirya-1 Varity performs well under
drought stress condition.
3. DISCUSSION
The four selected wheat genotypes under different drought level showed
significant difference regarding physiological parameters. Chlorophyll
“a” and chlorophyll “b” is one of the events which are used for
showing of water stress. The genotypes and stress level show different
results regarding chlorophyll content. Data concerning Chlorophyll “a”
and “b” presented in Table 1 demonstrated that there were significant
differences in chlorophyll “a” and “b” after different level of
drought stress. The data regarding total chlorophyll presented in (Table
1) revealed that drought stress affect the total chlorophyll content.
Similar results under different drought level were observed by (Kumaret al. , 2013) that chlorophyll content of leaf was demolished
under drought stress treatment and also stops it from making. A number
of investigators have observed that harm to chlorophyll content of leave
as a result of drought stress (Arjenaki et al. , 2012; Nilsen and
Orcutt, 1996). The cause for decrease in chlorophyll content of leaves
as affected by water scarcity is that due to drought treatment reactive
oxygen species (ROS) such as O2- and H2O2, was produced in which an
escort to lipid peroxidation and as a result, chlorophyll demolition
(Saeidi et al. , 2015; Foyer et al. , 1994; Schlemmeret al. , 2005) also reported that drought stress highly affect
chlorophyll content in which changing the green color of leaf into
yellow color, the reflectance of the event radiation is enlarged.
Relative water content is the relation between fully turgid water
content and actual water content of plant tissues when they are
subjected to drought stress condition. Therefore leaf relative water
content indicates the ability of plants to keep their water status
adequate enough to sustain water stress. In the current research the
RWCs declined during water stress in all the studied wheat genotypes.
Similar results were reported by (Siddique et al. , 2001) that
drought stress condition considerably reduced the leaf potential and
relative water content and transpiration rate with an associated raised
in leaf temperature. This current result was also supported by the
statement of (Almeselmani et al. , 2011) that drought regime lead
to decrease status of water during the growth of crop, soil moisture
potential and plant osmotic potential for water and nutrient uptake
which finally moderate leaf turgor pressure as results metabolic
activities of crop was disturbed.
Membrane stability and integrity is one of the significant selection
measurements of non-irrigation stress charitable genotypes (Tripathyet al. , 2000). Because under water deficit environment membrane
stability and integrity sure water scarcity resistance (Bewley, 1979).
Analysis of variance (ANOVA) Water stress caused water loss from plant
tissues which seriously impair both membrane structure and function
(Cave et al. , 1981). Our results in agreement with (Vasquez-Telloet al. , 1990) that electrolyte leakage was correlated with
drought tolerance. Our results also support the finding of (Sayaret al. , 2008) that they reported drought stress highly effect the
membrane stability of the plant.
The results indicate that proline content was increased under drought
stress condition as compared to control condition. As drought condition
were increased the proline content were also increased. Our current
experimental work was also supported the finding of (Parida et
al. , 2007) that they reported that proline are highly accumulate in
drought stress condition.
Relative expression of six genes which encode proteins for LHCI and
LHCII were studied to check the effect of drought stress at molecular
level. As shown by semi-quantitative RT–PCR, that the expression
pattern was different among the studied genes in response to different
level of drought stress, and different level of genes expression was
observed. However it is observed that expression of each genes were
related to drought stress condition and the genotypes. The results
revealed that the Chirya-1 genotype perform well under water stress
condition followed by Synthetic derivatives genotypes. The results
regarding level of gene expression were related with the observation of
(Zhao et al. , 2007) who reported that in drought stress condition
the photosynthesis in the chloroplast is the most sensitive region. In
the previous work it was observed that expression level of genes in
Stay-Green was found to be greater than that of the wild type under
drought condition (Tian et al. , 2012). The genes involved in
LHCII namely TaLhcb1, TaLhcb4 and TaLhcb6 show higher
level of gene expression in Stay-Green genotype and similar results was
also observed by Tian et al . (2013) they observed higher level of
gene expression in Stay-Green Genotype as compare to wild type wheat
genotype. Our results revealed that LHCI genes TaLhca2,
TaLhca3 and LHCII genes TaLhcb4 and TaLhcb6 show up
regulation in SD-28, Opata and Chirya-1 and their expression level is
not affected by drought stress condition but TaLhca1 andTaLhcb1 are the most sensitive genes to drought stress condition.
In comparison the expression level of genes is more affected in SD-32
followed by Opata wheat genotype. The overall results regarding level of
genes expression is in general agreements with (Oksman-Caldentey and
Saito, 2005; Reinders and Sickmann, 2007) who reported that the levels
of regulation based on post-transcriptional and post-translational
mechanisms are involved in the abiotic stress response.