Hindawi Publishing Corporation
The Scientific World Journal
Volume 2013, Article ID 610721, 12 pages
http://dx.doi.org/10.1155/2013/610721

Review Article
Drought Tolerance in Wheat
Arash Nezhadahmadi, Zakaria Hossain Prodhan, and Golam Faruq
Institute of Biological Sciences, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
Correspondence should be addressed to Golam Faruq; faruq@um.edu.my
Received 29 July 2013; Accepted 6 September 2013
Academic Editors: R. S. Boyd and N. Rajakaruna
Copyright © 2013 Arash Nezhadahmadi et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Drought is one of the most important phenomena which limit crops' production and yield. Crops demonstrate various
morphological, physiological, biochemical, and molecular responses to tackle drought stress. Plants' vegetative and reproductive
stages are intensively influenced by drought stress. Drought tolerance is a complicated trait which is controlled by polygenes and
their expressions are influenced by various environmental elements. This means that breeding for this trait is so difficult and new
molecular methods such as molecular markers, quantitative trait loci (QTL) mapping strategies, and expression patterns of genes
should be applied to produce drought tolerant genotypes. In wheat, there are several genes which are responsible for drought
stress tolerance and produce different types of enzymes and proteins for instance, late embryogenesis abundant (lea), responsive
to abscisic acid (Rab), rubisco, helicase, proline, glutathione-S-transferase (GST), and carbohydrates during drought stress. This
review paper has concentrated on the study of water limitation and its effects on morphological, physiological, biochemical, and
molecular responses of wheat with the possible losses caused by drought stress.

1. Introduction
Drought is one of the most common environmental stresses
that affect growth and development of plants. Drought
continues to be an important challenge to agricultural
researchers and plant breeders. It is assumed that by the
year 2025, around 1.8 billion people will face absolute water
shortage and 65% of the world's population will live under
water-stressed environments. Tolerance to water stress is
a complicated parameter in which crops' performance can
be influenced by several characteristics [1]. Tolerance can
be divided into two parts including drought avoidance
and dehydration tolerance [2]. Drought avoidance includes
root depth, reasonable use of available water by plants,
and changes in plants' lifestyle to use rainfall. Dehydration
tolerance consists of plants' capability to partially dehydrate
and grow again when rainfall continues [3]. Adaption of
plants to drought stress is a vital issue to develop new
improve methods for increasing stress tolerant plants [4].
Many factors can affect plants' responses to drought stress
such as plant genotype, growth stage, severity and duration of
stress, physiological process of growth [5], different patterns
of genes expression [6], different patterns of the activity

of respiration [7], activity of photosynthesis machinery [8],
and environmental factors [4, 9]. Drought stress can have
effects on genes expression, and detection of genes during
water stress is crucial to observe their responses. In this
regard, various drought responsive genes were distinguished
[1]. Ouvrard et al. [10] believed that the role of genes can be
distinguished by expression of a gene to high resistance levels
among varieties. Drought stress can also influence plants in
terms of protein changes, antioxidant production, osmotic
adjustment, hormone composition, root depth and extension,
opening and closing of stomata, cuticle thickness, inhibition
of photosynthesis, decrease in chlorophyll content, reduction
in transpiration, and growth inhibition [11–14] to stand with
some osmotic changes in their organs. Drought can also
cause pollen sterility, grain loss, accumulation of abscisic
acid in spikes of drought-susceptible wheat genotypes, and
abscisic acid synthesis genes in the anthers [15]. In many
biochemical studies, the role of reactive oxygen species (ROS)
has been identified. Dat et al. [16] claimed that increase in
ROS can be caused by drought stress in which oxidative
balance of the cell is changed. A rise in the generation of ROS
prompts to the generation of ABA (abscisic acid) which is a
general signal under drought [17–20] and can consequently

2
regulate the antioxidant genes expressions by producing
superoxide dismutase (SOD) and catalase (CAT) [21]. Several
physiological studies have been completed on the impact of
drought stress on wheat. Rosenberg et al. [22] observed that
transpiration decreased significantly under drought stress;
then heat can slowly be lost from the leaves and leaf
temperature can be increased. As a result, CO2 concentrations and photosynthesis are increased which affect plant's
growth and finally, water use efficiency can be improved.
The same studies demonstrated that plants' development
can be promoted more with CO2 [23–26]. A respiratory
terminal oxidase, alternative oxidase (AOX), plays important
roles in optimizing photosynthesis and protecting chloroplast
under drought stress [27]. Ribas-Carbo et al. [7] suggested
that the increase in AOX pathway under water stress could
be prompted by the inhibition of cytochrome pathway. In
this review paper, an attempt is made to explore different
research information on wheat drought tolerance in various
aspects, namely, morphological, physiological, biochemical,
and molecular responses.

2. Physiological Derivations of Drought
Tolerance in Wheat
Physiological responses include closure of stomata, decrease
in the activity of photosynthesis, development of oxidative
stress, alteration in the integrity of cell wall, production of
metabolites which are toxic and cause plants' death [28],
signal recognition of roots, turgor loss and adjustment of
osmosis, reduction in water potential of leaf, decrease in
stomata conductance to CO2 , reduction of internal CO2
concentration, and reduction of growth rates. According to
researchers, there is a relationship between different physiological responses of crops and their resistance functions
under drought such as high amount of relative water and
potential water [29, 30] and integrity of membrane [31,
32]. For measuring drought tolerance, various scientists
considered maintenance of membrane integrity and its role
under water stress [33, 34]. Sink strength can be reduced
in drought stress during early grain filling which results
in reducing endosperm cell number and metabolic activity
[35]. Grudkowska and Zagda´ ska [36] indicated that cysteine
n
proteinase plays an imperative function in plant signalling
pathways, growth and development, and in the response
to various kinds of stress. Cysteine is expressed in wheat
leaf organs and its contribution in proteolysis activity rises
under drought [37]. Wi´niewski and Zagda´ ska [38] also
s
n
observed that the role of cysteine was improved, but its role
was negatively related to the degree of drought tolerance
of ten lines of spring wheat. Transpiration efficiency (TE)
is indispensable phenomenon in plants. Various researchers
proposed that TE can be influenced by cultivar and drought
[39, 40]. So, the selection of high TE crops is the most
important action to produce drought tolerant plants. Growth
is one of the physiological processes which is sensitive to
drought and can be affected by reduction in turgor pressure.
Because of low turgor pressure, water stress quenches cell
expansion and growth. However, when turgor pressure is

The Scientific World Journal
Table 1: Yield losses at vegetative growth stages under drought in
wheat.
Vegetative stage
Early season stress
Midseason stress
Booting stage
Tillering stage
1000-grain weight (vegetative stage)
Earlier stages
Spike length (vegetative stage)
Number of spikelets per spike
(vegetative stage)
Grains number (vegetative stage)
Grain yield (vegetative stage)

Yield loss (%)

Reference

22
58
20.74
46.85
38.67
79.7
16.90

[48]
[48]
[49]
[49]
[50]
[51, 52]
[50]

28.63

[50]

72.51
61.38

[50]
[50]

Table 2: Yield losses at reproductive growth stages under drought
in wheat.
Reproductive stage
Higher grain protein content, fewer
days to physiological maturity,
smaller kernel weight and diameter,
less grain yield
Less grain yield (drought-tolerant
variety)
Less grain yield (drought-sensitive
variety)
1000-grain weight
1000-grain weight (anthesis stage)
Biological yield
Maximum grain yield
Decreased seed number
Grain formation stage
Grain formation stage
Number of spikes
Number of spikes (anthesis stage)
Spike length (anthesis stage)
Number of spikelets per spike
(anthesis stage)
Grains number (anthesis stage)
Grain yield (anthesis stage)

Yield loss (%)

Reference

Not applicable

[53]

43

[54]

26

[54]

18.29
5
38.67
10
22
64
101.23
65.5
19.85
15.79
16.90

[1]
[3]
[50]
[1]
[1]
[3]
[49]
[51, 52]
[50]
[50]
[50]

26.20

[50]

72.51
64.46

[50]
[50]

bigger than the cell wall yield, cell expansion can occur
[41, 42]. Osmotic adjustment is a remarkable part of plants'
physiology by which they respond to water deficits [5, 43–
47]. Yield losses at vegetative growth and reproductive stages
under drought in wheat are provided in Tables 1 and 2.

3. Biochemical Derivations of Drought
Tolerance in Wheat
A reduction in efficiency of photochemical, reduced Rubisco
efficiency, gathering of stress metabolites (glutathione,

The Scientific World Journal
MDHA, glybet, and polyamines), antioxidative enzymes
(superoxide dismutase (SOD), peroxidase (POD), catalase
(CAT), ascorbate peroxidase (APX), glutathione reductase
(GR), glutathione-S-transferase (GST), glutathione peroxidase (GP)), monodehydroascorbate reductase (MDHAR),
and reduced ROS accumulation are biochemical responses
of plants to water stress. Tolerance to drought correlates with
a positive response of plants' antioxidant system. According
to the study of Li and Staden [55], in drought condition,
some reactive oxygen species (ROS) such as hydroxyls (OH),
superoxide (O2 − ), peroxide hydrogen (H2 O2 ), and oxygen
which is singlet (1 O2 ) are created. These ingredients may
initiate disturbing lipid peroxidation, chlorophyll, protein
oxidation, and nucleic acids [56]. Changes in activity of these
enzymes are crucial for the resistance of various plants to
drought stress [57]. Evidences suggest that drought causes
oxidation damage from increased production of ROS with
deficit defense system of antioxidant in plants [54, 58–61].
Osmotic regulators include small molecules (Pro), ions
(K+), and soluble sugar, which help crops to absorb water in
drought environments. In wheat, various studies exhibited
that wheat genotypes with higher osmotic regulators and
lower malondialdehyde (MDA) content have better tolerance
to drought [5, 43, 47, 60, 62–66]. Polyamines (PAs) have
a role in the completeness of membranes and nucleic acid
under water stress environments [11]. Malabika and Wu [67]
mentioned that higher levels of polyamines can make crops
have higher growth under water stress conditions [18, 68, 69].
CAT is one of the most rapidly reversible proteins in leaf
cells especially in stress conditions and its activity is reduced
in drought condition [70].

4. Morphological Derivations of Drought
Tolerance in Wheat
According to the study of Deˇ ci´ et al. [71], wheat is
n c
paid special attention due to its morphological traits during
drought stress including leaf (shape, expansion, area, size,
senescence, pubescence, waxiness, and cuticle tolerance) and
root (dry weight, density, and length). Shi et al. [72] expressed
that drought can affect vegetative and reproductive stages.
Therefore, understanding plants' responses to drought at
every life stage is crucial to progress in genetic engineering
and breeding. Rizza et al. [50] observed that early maturity,
small plant size, and reduced leaf area can be related to
drought tolerance. Lonbani and Arzani [73] claimed that the
length and area of flag leaf in wheat increased while the width
of the flag leaf did not significantly change under drought
stress. Leaf extension can also be limited under water stress
in order to get a balance between the water absorbed by
roots and the water status of plant tissues [74]. According to
the study of Rucker et al. [75], drought can reduce leaf area
which can consequently lessen photosynthesis. Moreover, the
number of leaves per plant, leaf size, and leaf longevity can
be shrunk by water stress [76]. Singh et al. [53] observed
that leaf development was more susceptible to water stress in
wheat. Root is an important organ as it has the capability to
move in order to find water [77]. It is the first organ to be

3
induced by drought stress [78]. In drought stress condition,
roots continue to grow to find water, but the airy organs are
limited to develop. This different growth response of shoots
and roots to drought is an adaptation to arid conditions
[79, 80]. To facilitate water absorption, root-to-shoot ratio
rises under drought conditions [81, 82] which are linked to
the ABA content of roots and shoots [83]. The growth rate
of wheat roots was diminished under moderate and high
drought conditions [84]. In wheat, the root growth was not
markedly decreased under drought [85]. Plant biomass is a
crucial parameter which was decreased under drought stress
in spring wheat [86]. The same outcomes were observed in
previous studies in wheat and other crops [86–88]. In winter
wheat, the yield was decreased or changed under drought
and, in contrast, the water use efficiency was boosted [89, 90].

5. Molecular Responses of Drought
Tolerance in Wheat
Some genes are known to be drought influenced and produced different types of drought stress related proteins and
enzymes including dehydrins [91], vacuolar acid invertase
[92], glutathione S-transferase (GST) [93], and late embryo
abundant (LEA) protein [94]; expression of ABA genes and
production of proteins like RAB, rubisco, helicase, proline,
and carbohydrates are molecular basis of drought tolerance.
Plants respond to stress environments with altering their gene
expressions and protein productions. In contrast, available
information on drought-responsive genes is still limited as
their roles have not been thoroughly determined [28]. In
wheat seedling stage, a lot of studies are done in gene
expression, but it is the junction stage that is susceptible to
drought [72]. This is because junction phase is the linkage
point in the vegetative and flowering growth stages and it is
important for development and reproduction [72]. Sivamani
et al. [52] indicated that HVA1 gene assists to increase wheat
growth under drought stress. HVA1 gene produce a kind
of protein which is in group 3 LEA and has 11 amino acid
motifs in nine repeats. Proline is a crucial protein that has
a vital function in water stress tolerance. It can be created
from pyrroline-5-carboxylate synthetase or P5CR, and the
responsible gene for this enzyme has been distinguished in
some crops, namely, petunia, soybean, and tobacco [95–97].
Hong-Bo et al. [98] investigated the role of proline as a wheat
antidrought defence protein under drought. In photosystem
II (PS II) reaction center, psbr has an indispensable task
in oxidation of water [99], and in Calvin cycle, rubisco
is the key enzyme under drought stress [100]. Some plant
proteins can be over-expressed including late embryogenesis
abundant (LEA) that are saved in vegetative tissues during
desiccation of seeds under drought stress. LEA proteins
are influenced by drought stress and their size in wheat
reaches 200 kDa (Wcs200) [101]. These proteins have been
detected through their sequence of amino acid [102] and
they help other proteins retrieve after denaturation during
water stress [103]. There have been a lot of works during
the last two decades to engineer LEA producing genes
for promoting crop water stress resistance. For instance,

4
wheat LEA genes, PMA1959 (encoding group one of LEA
protein) and PMA80 (encoding LEA protein's second group)
improved water deficit resistance in rice [104]. In wheat,
protein contents of groups one, two, and three of LEA have
been detected. The Em gene of wheat which encodes LEA
protein first group has been vastly researched [105–107].
Group three of LEA protein has also been distinguished
in seedlings of wheat [108, 109]. In durum wheat, protein
of groups two (dehydrins) and four of LEA proteins were
studied by Ali-Benali et al. [110]. Td27e, Td29b, and Td16 gene
transcripts were saved late in embryogenesis and throughout
seed development. Transcripts of Td11 gene were presented
whereas no transcripts of Td25a gene were detected in seeds
[110]. Vacuolar H+ -translocating pyrophosphatase (V-PPase)
is an important enzyme linked to plant development as
well as resistance to abiotic stress. Wheat V-PPase genes,
TaVP3, TaVP2, and TaVP1 were investigated by Wang et al.
[111]. Kam et al. [112] also detected the responsible genes
in wheat for water stress. They observed that TaRZF70 as
a RING-H2 zinc finger gene presented various responses
to drought stress which was upregulated in the leaf and
downregulated in the root [113]. TaRZF38 and TaRZF70 were
expressed in the wheat root while TaRZF74 and TaRZF59
were expressed in embryo and endosperm at the highest
level. TACCGACAT, the 9-bp consensus sequence, was first
distinguished in the promoter of Arabidopsis rd29A/lti78 and
presented to be vital for drought induction in abscisic acid
absence [114]. Then, this element could be bent by a family
of transcription elements and therefore named DRE-binding
(DREB) proteins [115]. Lucas et al. [116] used a sequence of
putative DREB labelled DREB3A from wheat (TaDREB3A,
Gen bank ID: AY781349) to seclude a DREB from wild wheat
(T. turgidum ssp. dicoccoides) and to detect its function in
higher drought resistance. They also concluded that DREB
proteins are numerous and vastly upregulated in reaction to
drought in root tissue rather than leaf [116]. Drought stress
influences RD gene (responsive to desiccation) [117, 118]. This
gene has been divided into two major parts. The first group
includes expression of regulatory gene and signal direction
during the crops' reaction to stress, and the second group
involves proteins which directly protect cells from stresses
[119]. In wheat, among 265 genes detected at the junction
phase and 146 genes distinguished at the seedling stage in
response to drought stress, more than half of them were
thought to be involved in abiotic or biotic stress responses
[72].

6. Breeding for Drought Tolerance
through Conventional and
Biotechnological Breeding Methods
Conventional breeding needs the detection of genetic variability under drought between plant genotypes, or between
sexually compatible cultivars, and introduction of tolerance
line with proper agronomic traits. Although conventional
breeding for water stress resistance has had some prosperity,
it is a slow process which is limited by the availability of
proper genes for breeding. In traditional breeding, crosses are

The Scientific World Journal
partially uncontrolled and breeders select parents to cross,
but at the genetic approach, the outcomes are unpredictable
[120]. Conventional breeding strategies are labour-intensive
which requires great efforts to separate undesirable traits
from desirable traits, and this is not economically suitable.
For instance, crops must be back-crossed again over lots
of growing seasons to breed undesirable traits generated by
random mixing of genomes [120]. On the other hand, the
improvement of resistant plants through genetic engineering
needs detection of important genetic dominants to respond as
stress resistance crops by transferring novel genes into plants.
Drought affects the activity of a vast number of genes, and
gene expression experiments have detected various genes that
are induced and repressed under drought stress [121]. The
nature of drought tolerance makes the management difficult
in traditional breeding techniques. Novel biotechnological
strategies have increased information on crop responses to
drought at whole crop and molecular levels [122]. A lot of
drought stress-induced genes were detected and cloned. Crop
genetic engineering and molecular-marker methods make
the improvement of drought-resistant germplasm possible
[122]. Transgenic crops are also being improved to manage water stress. Structural and regulatory genes including
dehydration-responsive, element-binding (DREB) factors,
zinc finger proteins, and NAC transcription factor genes
are already being applied [122]. Agrobacterium and particle
gun techniques for transgenes related to drought resistance
were applied in different crops such as rice, wheat, maize,
sugarcane, tobacco, Arabidopsis, groundnut, tomato, and
potato. Drought-tolerant genetically modified (GM) plants
are being produced and molecular markers are used to detect
drought-related quantitative trait loci (QTL) which were
successfully transferred into rice, wheat, maize, pearl millet,
and barley [122].

7. Breeding for Drought Tolerance through
Molecular Markers in Wheat
Nowadays, molecular markers are widely used to detect
the location of drought-induced genes. Different molecular
marker are currently available for genome mapping and
tagging of different traits which is useful for Marker-assisted
breeding (MAB) technique in wheat in stress conditions
[123]. It is intensively used to create stress-tolerant lines
in different crops. Marker-assisted selection (MAS) refers
to selection by DNA markers linked to QTLs that are
very powerful. Thus, DNA markers can track presence of
QTLs for drought tolerance [124, 125]. For development of
drought tolerance in plants through molecular linkage maps,
marker-assisted selection (MAS) is the best procedure. In
winter wheat, with the use of amplified fragment length
polymorphism (AFLP) and simple sequence repeat (SSR)
markers, QTL mappings for senescence of flag leaf (FLS) in
normal and water-stressed environments have been studied.
The responsible gene for this characteristic is revealed and
the QTL is also detected on chromosome 2D associated with
better performance under drought [126]. In another study by
Quarrie et al. [127], DNA markers like restriction fragment

The Scientific World Journal
length polymorphism (RFLP), AFLP, and SSR have been used
to tag QTLs for drought stress in wheat. During the last few
decades, molecular markers such as SDS-protein, isozymes,
and DNA sequences have assisted to select quantitative traits
especially drought tolerance. These molecular markers are
used in wheat to evaluate diversity of genes and identify
genotype and genetic mapping [128–130]. Some markers in
durum wheat are linked to grain yield and morphophysiological characteristics for drought tolerance [131]. Leaf water
potential, canopy temperature, chlorophyll inhibition, and
proline content showed strong relationships with molecular
markers [131]. Ashraf et al. [132] prepared various DNA
markers to estimate inheritance of stress tolerance such as
PCR indels, RAPDs, RFLPs, CAPS, AFLPs, microsatellites
(SSRs), SNPs and sequences of DNA. In cereals, RAPDs with
the use of DNA primer were vastly used [133, 134]. ISSRs
were used in mapping of genome in wheat and other crops
[135, 136]. Milad et al. [48] identified RAPD and ISSR markers
related to flag leaf senescence gene in wheat under drought
stress. RAPDs were found to be helpful in hexaploid wheat
as genetic markers [134, 137]. When the correlation between
a molecular marker and a trait is greater than the heritability
of the trait, marker assisted selection may be advantageous.
These results suggest the usefulness of molecular markers
to enhance drought tolerance in durum wheat in drought
condition [131].

8. Mapping of QTL for Drought
Tolerance in Wheat
Quantitative trait loci (QTL) is a location from where some
genes influence a phenotype of quantitatively inherited trait.
Genetic variations of a crop can be explored through QTL
mapping (polygenes) [132]. Mapping of QTL allows the
estimation of the places, quantity, size of effects for the
phenotype, and gene activity pattern [138]. In 2005, the
first activity was conducted for cloning QTL [139] to know
and operate the characteristics which are responsible for
drought resistance [51, 140, 141]. QTL mapping for water
stress resistance traits has been done in wheat and other
crops [142–147]. In wheat, due to drought stress, the place
of genes which had influence on ABA concentration was
detected [142]. It is detected that 5A chromosome transports
gene(s) for ABA concentration. Quarrie et al. [127] conducted
mapping of QTLs for drought resistance in hexaploid wheat
placed on chromosomes 1A, 1B, 2A, 2B, 2D, 3D, 5A, 5B,
7A, and 7B. Double haploid populations serve as a permanent source of QTL mappings. Recombinant inbred lines
from crossing of drought-resistant and drought-susceptible
cultivars were used to create mapping populations for QTL
analysis regulating yield under drought [148]. QTL analysis
is so important to target genes and for doing this some steps
are required. Firstly, phenotypic evaluation of relatively large
population for markers which are polymorphic is needed.
Secondly, genotyping of the population is important. Thirdly,
there is a need for statistical analysis to detect the loci that
are influencing the target trait. On the other hand, QTL
for drought tolerance has some drawbacks like genetic and

5
environmental interactions, numerous numbers of genes,
and using of mapping populations which are wrong. These
have limited plans for mapping of QTL for high yield under
drought condition [149].

9. Drought Management
9.1. Drought-Tolerant Varieties. In the past decade, there
have been several efforts to generate drought-tolerant wheat
through breeding methods. Cross-breeding among wild
wheat species at the International Centre for Agricultural
Research in the Dry Areas (ICARDA) created germplasm
that creates higher yields under drought. In wheat breeding
programs, seeking for increased yield has been a priority
to improve drought tolerance of plants. However, before
successful genetic manipulation can be made, it is important
to characterize the physiological parameters of droughttolerant or -sensitive cultivars [150]. Analysing physiological
determinants for yield which responds to water stress may
also be helpful in breeding for higher yields and stability of
genotypes under drought conditions. Traits to select either
for stress escape, avoidance or tolerance, and the framework
where breeding for drought stress is addressed will depend on
the level and timing of stress in the targeted areas. However,
selecting for yield itself under stress-alleviated conditions
appears to produce superior cultivars, not only for optimum
environments, but also for those characterized by frequent
mild and moderate stress conditions [150]. This implies that
broad avoidance/tolerance to mild/moderate stresses is given
by constitutive traits also expressed under stress-free conditions [151]. Keeping in view the importance of identifying
water-stress tolerant wheat genotypes, water stress conditions
can be imposed to wheat at various stages of crop growth and
development. The stresses can be given at tillering, booting,
and grain forming stages. Root system size (RSS) of wheat
can be a selection target for drought tolerance. During dry
periods, crops expand their roots to deeper soil regions
and they are able to alter their morphology. For instance,
the airy organ mass is decreased but the mass of roots is
increased. Wheat genotypes with good water management
are able to bear high yields in drought conditions [152].
Genotypes with proper water management could be used
to create new breeding lines and cultivars with developed
drought resistance.
9.2. Agronomic Practices. Drought stress includes different
agronomic, soil, and climatic factors which vary in the
time of occurrence, duration, and intensity. It has effect
on yield and can also diminish benefits of crop handling
performances including management of fertilizer or pest
and disease [49]. Drought management strategies are very
important and have to concentrate on extraction of available
soil moisture, crop establishment, growth, biomass, and grain
yield. There are many agronomical ways to manage drought
stress such as control of field irrigation methods (surface or
furrow, sprinkled, and drip) and identification of drought
resistance sources through developing screening methods
under environmental conditions. So, for drought screening,

6

The Scientific World Journal

Table 3: Research scenario of physiological traits under drought
stress in wheat.

Table 5: Research scenario of morphological traits under drought
stress in wheat.

Traits
Physiological
Stomata closure
Cell wall integrity
Synthesis of metabolites
Oxidative stress
Photosynthesis
Turgor pressure
CO2 concentration
Growth rate
Osmotic adjustment
Stomata conductance
Relative water content
Membrane integrity
Transpiration
Water use efficiency
Transpiration efficiency
Total biomass
Alternative oxidase (AOX)

Traits
Morphological

Reference
[16]
[16]
[16]
[16]
[16, 45, 62, 115]
[64, 71]
[30, 46, 73, 84]
[92]
[21, 42, 62, 81, 88, 89, 97]
[62]
[26, 110]
[36, 72, 102, 119]
[115]
[13, 69, 153]
[121, 124]
[13, 154, 155]
[108, 156]

Reference

Small plant size
Leaf area

[112]
[112, 116]

Root extension
Roots dry weight, density, and length
Early maturity

[75, 135, 143, 160, 161]
[35]
[112]

Yield
Leaf extension
Leaf size

[69, 90, 128, 153]
[95]
[133]

Leaf number
Leaf longevity

[133]
[133]

Root-to-shoot ratio

[88, 91]

Table 6: Research scenario of biochemical traits under drought
stress in wheat.
Traits

Reference

Biochemical
Table 4: Research scenario of molecular traits under drought stress
in wheat.
Traits

Reference

Molecular
CAT gene expression
SOD gene expression
Proline
Dehydrins
Vacuolar acid invertase
Glutathione S-transferase (GST)
Late embryo abundant (LEA)
DRE-binding proteins
Rd29A/Lti78
Psbr
Rubisco
QTL mapping
Molecular markers

[66]
[66]
[57, 114, 157]
[2, 27]
[150]
[5]
[17, 40, 98]
[78]
[158]
[142]
[43]
[8, 9, 12, 19, 44, 103, 122, 123, 125,
126, 145, 146, 149, 151, 152, 159]
[9, 44, 146]

not only analysing sources of replications, variation among
plots, and repeated experiments are needed, but also sprinkler irrigation, rainout shelters, and evaluation of drought
susceptibility index (DSI) are important [49]. In drought
management strategies, increasing biomass and seed yield,
crop establishment, and maximum crop growth have to be
considered. For example, to improve yield in drought-prone
area, these steps are essential: frequency of drought stress
occurrence in the target environment, matching phenology
of crop (sowing, growth period, flowering, and seed filling)
with period of soil moisture and climatic regimes, developing
a way for the better use of irrigation, and increasing soil
water to crop through agronomic management practices.

Chlorophyll content
Superoxide Dismutase (SOD)
Catalase (CAT)
Polyamines (PAs)
Reactive oxygen species (ROS)
Abscisic acid (ABA)

[75, 100, 127, 143, 160, 161]
[66]
[59, 66]
[4, 14, 82, 136, 143]
[22, 24, 31, 32, 56, 76, 96,
107, 127, 132, 136, 139, 162]
[32, 56, 96, 136]

Furthermore, good knowledge of what type of stress is
more frequent in target environment is essential in drought
breeding. Yield stability under water shortage condition and
crop water productivity should be the goal. In drought
stress condition, the aim is to preserve the source of water.
These sources include snow, rain, and irrigation water. Water
conservation can be achieved by surface residue during the
growing season. Todd et al. [163] claimed that wheat residue
diminished the evaporation rate during the season. Residue
also slows movement of water and allows much time for the
water to penetrate into the soil. Rotation of crop can preserve
the total water needs by irrigation. In winter wheat, it can be
decline requirements for irrigation. Schneekloth et al. [159]
claimed that with irrigation for 6 inches, corn following wheat
produced 8 percent more than corn following corn. Rotation
of crops also makes the irrigation season to have much
time frame in comparison with a single crop. In breeding
for drought resistance, productions of biomass and water
use efficiency (WUE) are imperative elements of agronomy
[155]. There is a risen interest in improving WUE of plant
genotypes so that plants can develop and bear better under
drought condition [154, 164]. Figure 1 shows the effects of
drought stress on different wheat traits. Detailed information
on physiological, molecular, biochemical, and morphological
traits under drought stress in wheat is demonstrated in Tables
3, 4, 5, and 6.

The Scientific World Journal

7

Water stress
Morphological changes
- Small plant size
- Early maturity
- Reduced leaf area
- Reduced yield
- Limited leaf extension
- Diminished leaf size
- Decreased number of leaves
- Reduced leaf longevity
- Increased root-to-shoot ratio
- Reduced total shoot length
- Decreased plant height

Physiological changes
- Stomata closure
- Diminish in photosynthesis
- Increase in oxidative stress
- Cell wall integrity changes
- Leaf water potential reduction
- Decrease in stomata
conductance
- Internal CO2 concentration
reduction
- Diminished growth rates
- Decline in transpiration
- Developed water use
efficiency
- Enhance of AOX
pathway
- Reduced relative water
content

Biochemical changes
- Reduction in rubisco
efficiency
- Declined photochemical
efficiency
- Produced reactive oxygen
species (ROS)
- Oxidation damage
- Antioxidant defense
- ABA generation
- Diminished Chlorophyll
content
- Proline production
- Polyamines generation
- Increase in antioxidative
enzymes
- Carbohydrates production
- ABA accumulation

Overcome
- Classical genetic methods
- Responsible genes detection and transgenic plants production which lead to overexpression of
compatible solutes in transgenic plants to improve stress tolerance
- Manipulation of genes
- Improved plant breeding techniques (water extraction efficiency, water use efficiency, hydraulic
conductance, osmotic and elastic adjustments, and modulation of leaf area)
- Appropriate agronomical practices

Figure 1: The effect of drought stress on wheat. The information are provided from the observations of Powel et al. [128], Lawlor and Cornic
[13], Shiran and Wan [15], Karthikeyan et al. [41], and Russell et al. [129].

10. Conclusion
Detection of genomic responses of plants to water stress
is so important. Firstly, it prepares intensive information
about transcriptional reactions of plants to drought stress.
Secondly, it makes possible to know functions of genes
in stress environments. Thirdly, it assists to distinguish
promoters which react to stress and related cis-elements,
which are both crucial for primitive studies and crop engineering [165]. Rapid improvements can be performed in
drought resistance by manipulating the genes which are
responsible for the plant growth regulators, antioxidants,
proteins, and transcriptional factors [149]. QTL analysis and
molecular mapping are also proper methods which have
been done for qualitative and quantitative characteristics
including resistance for stress. But, there are some limitations
in this issue. For example, there is a challenge for QTL
detection, for instance, interaction between genotype and
environment, inconsistent repeatability, numerous genes that
regulate yield, and use of wrong populations for mapping.
Furthermore, other elements also limit the efficiency of QTL
for genetic development of a parameter because of improper
interaction epistasis, it is difficult to carry the influences
of an allele to extract substance [156, 166]. Moreover, in
several circumstances, QTL does not present marked impacts
and stop thoroughly in various groundwork, even in similar
growth conditions [153, 156]. This high variability in the
nature of water stress and inadequate information about its

complicatedness have caused it to be hard to identify specific
physiological traits needed for improved crop performance.

Acknowledgment
The authors wish to express their gratitude to the University
of Malaya, Kuala Lumpur, Malaysia, for providing IPPP Grant
no. PV0138-2012A for this paper.

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