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*Corresponding author: E-mail: igali@mautch.edu.ng, igali@mautech.edu.ng;
Asian Plant Research Journal
5(2): 34-46, 2020; Article no.APRJ.56829
ISSN: 2581-9992
Biotechnology and Drought Stress Tolerance in
Plants
Gali Adamu Ishaku
1*
, Daniel Thakuma Tizhe
1
, Raji Arabi Bamanga
1
and Elizabeth Toyin Afolabi
2
1
Department of Biotechnology, School of Life Sciences, Modibbo Adama University of Technology,
Yola, Nigeria.
2
Department of Crop Production, School of Agriculture and Agricultural Technology, Modibbo Adama
University of Technology, Yola, Nigeria.
Authors’ contributions
This work was carried out in collaboration among all authors. Authors GAI and DTT Designed the
study, wrote the protocol and wrote the first draft of the manuscript. Authors RAB and ETA managed
the literature searches. All authors read and approved the final manuscript.
Article Information
DOI: 10.9734/APRJ/2020/v5i230104
Editor(s):
(1)
Dr. Suleyman AVCI, Eskisehir Osmangazi University, Turkey.
Reviewers:
(1) Yin Feng Xing, China.
(2)
Manju Sharma, Amity University, India.
Complete Peer review History:
http://www.sdiarticle4.com/review-history/56829
Received 05 March 2020
Accepted 12 May 2020
Published 22 June 2020
ABSTRACT
Drought stress in plants has become one of the major abiotic stress that limits the growth and
development of plants which also contributes to low yields. Biotechnology which has new and
emerging techniques can be use to solve the problem of drought stress in plants. This review aimed
at identifying drought stress tolerance in plants at different stages, how plants respond to drought
stress using different methods and the application of different biotechnology methods to improve
drought tolerance in plants. Some important parameters about drought stress in plants such as
drought tolerance mechanisms, plants responses to drought stress, gene regulation for drought
stress tolerance in plants, effects of drought stress at different stages of plant growth and
biotechnology methods in developing drought tolerance in plants was reviewed. The use of
biotechnology methods such as classical breeding, use of genetic manipulation, genes from
resurrection plants and Protoplast fusion was discussed. Drought stress affects our plants seriously
and it leads to wilts, reduction of yields and death of plants at different developmental stages.
Plants have developed different mechanisms to respond to drought stress but these mechanisms
Review Article
Ishaku et al.; APRJ, 5(2): 34-46, 2020; Article no.APRJ.56829
35
are not sufficient enough without the application of biotechnology to greatly improve the growth,
development and increase yield in pants. The use of biotechnology greatly improves plants ability to
tolerate drought stress depending on the plant species and period of exposure. The use of
biotechnology methods has become very vital in improving plants drought stress so as to overcome
the major problems of plants which includes increase in population and climatic change.
Keywords: Biotechnology; classical breeding; genetic manipulation; plant drought stress; protoplast
fusion and resurrection plants.
1. INTRODUCTION
Drought is the water deficit that impairs plants
growth, development and yield compared with
the normal water supply required for optimum
growth. The drought which is an abiotic factor is
one of the most common stresses that greatly
hampered plants growth and development
compared to other types of plant stresses [1,2].
Drought induces metabolic changes in plants,
such as increased levels of free sugars and free
essential amino acids, which according to the
"Plant stress hypothesis" causes the plant to
have a higher nutritional value for herbivores and
can play an important role in herbivore outbreaks
[3]. Drought stress is usually said to be an
extremely dry condition beyond a threshold level
which causes damage to plants. When plants
lack adequate water supply, the resulting drought
stress normally reduces growth more than all
other plant abiotic stresses. Plant responds to
lack of water by reducing the activities of
photosynthesis and other plant processes. When
plants experience drought stress and water loss
progresses, leaves of some plant species appear
to change colour (usually to yellow-brown) and
drought stress also reduces crop productivity or
yield [4,5]. Drought stress also plays a vital role
in determining the availability of most plants
species across different locations in the world.
Naturally, drought stress in plants varies from
species to species, a period of exposure and
some environmental parameters. Plants
tolerance to drought stress is a relevant issue
that requires new improve techniques like
biotechnology to enhance stress-tolerant [6]. The
most common factors that influence plants
tolerance to drought stress includes; the
physiology of the plant, the extent of the plant
stress, the growth stage, gene expression, the
specie of the plant, etc [7].
In this review, some important parameters about
drought stress in plants such as drought
tolerance mechanisms, plant responses to
drought, gene regulation for drought stress
tolerance in plants, effects of drought stress at
different stages of plant growth and
biotechnology methods in developing drought
tolerance in plants was discussed.
2. DROUGHT TOLERANCE
MECHANISMS IN PLANTS
Plants exposed to drought stress can tolerate
(adapt) to the stress depending on the plant
species and period of exposure which the plants
may survive under drought stress through the
induction of diverse biochemical, physiological or
morphological factors [8]. Phenotypic and
morphological changes that often occur in plants
are influenced by a spectrum of physiological
and molecular interactions developed to
acclimate to drought stress [9]. Drought stress
tolerance is the ability of a plant to grow, develop
and thrive with displayable economic yield and
value under limiting or no water supply [8].
Drought stress affects not only the water
relations of plants at cellular and tissue levels but
also at organ levels, which may result in explicit
and/or relatively ambiguous interactions that can
damage or acclimatize the plant [10].
Plants often respond to abiotic stresses through
the expression of stress-regulated genes and
protein production. The available data on stress-
related genes is still limited as their functions
have not been thoroughly established [7].
However, it has been established that plants'
ability to tolerate drought stress is a complex
event that involves a combination of some of the
genes to express synergistically. The expression
of genes may be triggered by stress-induced
events or result from injury responses to the
plant [8]. With the advent of genomics, some
genes are known to be expressed when plants
are drought-stressed to produce relevant drought
stress-related proteins and enzymes including
dehydrins (polypeptide), invertase, glutathione S-
transferase, and late embryogenesis abundant;
also, the expression of Abscisic acid (ABA)
genes which is an essential phytohormone that
regulates growth, development and adaptation to
drought stress and the synthesis of
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36
macromolecules such as rubisco, helicase,
proline, and carbohydrates are the molecular
basis of drought tolerance [7]. A polypeptide
(dehydrins) was observed to be the
most abundant among the accumulated
macromolecules in response to loss that leaves
water content in some plants (pea, maize, barley,
arabidopsis, etc) and under drought-induced
stress LEA proteins plays the protective role of
plants. In extreme cases even though they are
not plant specific, LEA proteins has been
associated with cellular desiccation tolerance.
Osmotin which is also a stress-responsive
antifungal protein accumulates under both biotic
and abiotic stress in several plant species [11].
Macromolecule such as phospholipids and
glycolipids are the lipid components of the plant
membrane layer, while triglycerides are primarily
used to store CH4 and CO2 during the
developmental stages of plants [12]. 70%-80% of
the total protein and lipid composition of leaf
tissue are found in the chloroplasts. Lipids, which
are one of the major components of the
membrane, are likely to be affected by water
stress [13].
3. PLANT RESPONSES TO DROUGHT
3.1 Physiological and Morphological
Responses
Plant growth and development is a process that
is usually accomplished through certain
physiological and morphological complex
interactions such as cell division, cell
enlargement, and differentiation, as well as
genetic interactions. The growth of a plant is
regulated by these activities as well as the
presence of organic and inorganic compounds
required for the development of new protoplasm
[14]. The quality and yield of plant growth to a
reasonable degree depend on these complex
interactions which can be greatly reduced by
drought stress [8].
The physiological response of plants to drought
stress can include; interference with
photosynthetic activity, stomatal regulation,
oxidative stress which eventually leads to
damage of the plant, generation of toxic
metabolites which can cause plant death [15],
water-retention level of leaf decreases, impaired
growth rate, decrease in CO
2
concentration, etc.
Cell growth and differentiation alongside other
physiological events are one of the most drought-
sensitive physiological events due to a decrease
in turgor pressure which is one of the major plant
responses to drought stress [16]. Water is
important in the maintenance of the turgor
pressure which is necessary for cell
enlargement, growth and for maintaining the
plant as a whole. Turgor is equally vital in
stomatal regulation and the motility of various
differentiated plant structures [17]. In extreme
drought stress, cell differentiation and elongation
of some plants are repressed through the
ongoing interference of water and minerals flow
from the vascular tissues to the other
components of elongating cells [18]. Severe
drought stress mostly is accompanied by
increased salt concentration which [14] defined it
as osmotic adjustment. Osmotic adjustment
occurs when solutes gradually accumulate in the
elongating cells of developing the plant as the
water retention level decreases over time.
Osmotic adjustment is one of the most essential
events in plant acclimatization to water-limitation,
for the reason that it maintained vascular tissue
metabolic activity and enables re-growth upon
water availability which of course varies greatly
from specie to specie [19].
3.2 Biochemical Responses
For decades, the complex interactions of
biochemical pathways that arise by drought
stress have become relevant [20]. Reactive
oxygen species are produced in different
compartments of the plant cell, both under
normal and stressful conditions. When plants are
stressed by drought or other abiotic stresses,
reactive oxygen species are generated as a
result of the inhibition of photosynthesis and the
preeminence of photorespiration. The generation
of reactive oxygen species is one of the earliest
biochemical responses of eukaryotic cells to
biotic and abiotic stresses. The production of
reactive oxygen species in plants, known as the
oxidative burst, is an early event of plant defense
response to water-stress and acts as a
secondary massager to trigger subsequent
defense reaction in plants. Reactive oxygen
species, which include oxygen ions, free radicals,
and peroxides, form as a natural byproduct of the
normal metabolism of oxygen and have an
important role in cell signaling. However, during
environmental stress such as drought, reactive
oxygen species levels increase dramatically
resulting in oxidative damage to macromolecules
such as proteins, DNA and lipids [21]. Being
extremely reactive, reactive oxygen species can
severely damage plants by increasing lipid
peroxidation, protein denaturation, nucleic acid
fragmentation and finally cell death. Drought
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37
stress induces oxidative stress in plants by a
generation of reactive oxygen species. Drought-
induced high production of reactive oxygen
species and it increases the content of
malondialdehyde. The content of
malondialdehyde has been considered as an
indicator of oxidative damage [22].
Reactive oxygen species are found to have a
dual function in plants: they are needed as
signaling molecules, but a high concentration it is
detrimental. High reactive oxygen species
concentration is therefore, a symptom of stress
and plants have to maintain the reactive oxygen
species within a certain level that is required for
normal cellular homeostasis. Reactive oxygen
species concentration in the cell is maintained by
the antioxidant system, which is made up of the
antioxidant molecules ascorbate, glutathione,
and α-tocopherol in addition to the antioxidant
enzymes peroxidases, catalases, and
dismutases [23]. In plants, reactive oxygen
species are discharged through certain
antioxidant molecules, polar and lipid-soluble
molecule [24], and the most effective antioxidant
being the process that counteracts oxidative
stress [8]. Most plants that are exposed to severe
environmental stresses notably as drought have
developed a mechanism to reprogram their
metabolic pathways to tolerate the impending
stress which often result in changes in the
production and utilization of available
metabolites. The advent of metabolomics has
uncovered how plants subjected to abiotic
stresses invest in the synthesis of essential
macromolecules and metabolites that contribute
to palliate stresses as osmoregulators,
antioxidants and defense compounds. Drought-
induced stress can also alter the available
content and composition of plants
macromolecules such as proteins which
eventually causes proportional changes of
structural and soluble proteins [25].
3.3 Gene Regulation for Drought Stress
Tolerance in Plants
The advent of whole-genome sequencing has led
to several drought-related candidate genes been
discovered and these genes have been
characterized [26]. The sequencing of model
plants such as Arabidopsis thaliana and Oryza
sativa marked a new era in plant biotechnology.
This post-genomic era is geared towards
establishing the functions of the entire genes
thought to be found in plants and hence, their
expression profiles. Genetic manipulation
associated with drought tolerance and other
abiotic stresses has become possible. Some
genes thought to be induced by abiotic stresses
have been reported [27] and some of these
drought-responsive genes were cloned and
characterized by a range of plant species [28].
The expression of these drought-responsive
genes to stress can be subjected to regulation
and coordination by modifying a gene for
tolerance under stress [29]. For efficient
tolerance and restoration of cellular activities in
plants under abiotic stresses, a gene that
encodes a stress-inducible transcription factor
that regulates other genes should be considered
[30]. The recent candidate genes for abiotic
stress used in plant genetic modification switch
on transcription factors for regulation and
expression of a range of genes for stress
tolerance [28]. These transcription factors
interact with cis-acting elements in the promoter
region of related genes and act synergistically to
enhance plant tolerance to a range of
environmental stresses. Majority of these
transcription factors that are induced by stress
can be broadly categorized into these families,
AP2/ERF, bZIP, NAC, MYB, MYC, Cys2His2,
zinc-finger and WRKY [31] DREB2s and
DREB1A are the largest subgroups of genes that
are involved in two different ABA-independent
pathways [32,33] involved in drought-responsive
gene expression in a transgenic plant.
4. EFFECTS OF DROUGHT STRESS AT
DIFFERENT STAGES OF PLANT
GROWTH
4.1 Seed and Seedling
Drought stress is one of the environmental
stresses in tropical regions that have a severe
limitation on plants growth, development and
yield. Plant responses to stress have become
one of the most research fields [52]. Studies
revealed that the most sensitive stage for
drought stress in a plant is the seed germination
and seedling stages [53] Drought stress has
been reported to greatly interfere with
germination and seedling phase [8]. Research on
physiological and biochemical responses under
water-limiting stress in the stages of seed
germination and early seedling growth becomes
relevant in full degree in reconciling and
identifying trends in early-stage and, to a certain
extent, in understanding the interior reasons for
low seedling establishment under natural
conditions [54]. These early growth stages are
important considering the effect of drought
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38
stress. The germination of the viable seed
depends to a large extent on the level of
moisture available in the soil for a physiological
and metabolic activity to breakdown the
dormancy of the dry seed. In plants, the
developmental stages which may involve
germination, seedling establishment, vegetative
growth and development of reproductive growth
stages can easily be impaired by limited water
supply [55]. Eck and Musick 1979 [56] reported
the effect of drought stress exposure on irrigated
sorghum seed at different stages of development
such as early boot, heading, and early grain
filling. According to their study, 35-42 days of
water stress exposure at boot stage significantly
decreased yield by 43% and 54% respectively.
Inuyama et al. [57] in a separate study for a
period of 16 days and 28 days under water
stress reported 16% and 36% reduction in yield
respectively at the vegetative stage of sorghum
development. Poor water supply reduces the
viability of seed and is directly linked with
seedling and post seedling crisis in plants [58].
The duration and exposure to drought stress are
directly linked with poor moisture intake,
germination and seedling establishment in maize
[55]. Roots and shoots elongations are elements
of seedling and their proliferation are subject to
drought stress [59]. Drought stress at seedling
stage will reduce seed endosperm weight, the
growth of the coleoptile, mesoctyl, radicle, shoot,
and root of sorghum [60]. Rizza et al. [61]
reported that drought stress can be related to
early maturity, small plant size and reduced leaf
area.
4.2 Growth and Development of Plant
Growth is an irreversible increase in size,
volume, and/or weight, which often involves the
spectrum of stages such as cell division, cell
elongation, and proliferation and cell
differentiation [62]. Growth and development of
plants may be greatly affected under drought
stress as a result of inhibition of enzyme
activities, reduced cell size and cell division,
reduced water potential and gradual decline in
energy supply [63]. The growth and development
of plants is vital for establishing proper and
normal plant structure that can carry out effective
physiological and metabolic interactions which
ultimately determines and give potential yields of
plants [22]. Water limitation severely interferes
with plant phenology where the plant phases of
growth are considerably reduced with a few
exceptions. Prolong drought stress initiate a
signal to cause an early switch from normal plant
developmental stages to vegetative reproduction
Table 1. Some drought-related responsive genes in plants
Gene
Gene expression
Plant
Nature
Reference
Adc Production of polyamine Rice Drought resistance [34]
AtTPS1 Trehalose-6-phosphate synthase Tobacco Drought resistance [35]
betA Choline dehydrogenase Maize Drought resistance [36]
mt1D Mannitol synthesis Wheat Drought and salinity
tolerance
[37]
P5CS Proline synthesis Petunia Drought resistance
and high proline
[38]
P5CS Proline synthesis Soybean Drought resistance [39]
PPO Polyphenol oxidases
suppression
Tomato Drought resistance [40]
HVA1 LEA protein Rice Drought and salinity [41]
ME-leaN4 LEA protein Chinese
cabbage
Drought and salinity
resistance
[42]
Apx3 Ascorbate peroxidase Tobacco Drought resistance [43]
ABF3 Transcription factor Rice Drought resistance [44]
Alx8 APX2 and ABA Arabidopsis Drought resistance [45]
AREB1 ABRE-dependent ABA signaling Arabidopsis Drought resistance [46]
DREB Transcription factor Arabidopsis Drought tolerance [47]
DREB1 Transcription factor Rice Drought, salt and
cold tolerance
[48]
DREB1A Transcription factor Tobacco Drought and cold
tolerance
[49]
DREB2A Transcription factor Arabidopsis Drought tolerance [50]
OsDREB1A
Transcription factor Arabidopsis
Drought, salt and
freezing tolerance
[51]
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39
Table 2. Effects of drought stress in some selected crop plants
Crop
Growth of stage
Reduction in yield %
References
Rice Reproductive 50–91 [65]
Rice Grain filling 60 [8]
Rice Reproductive 23–85 [66]
Maize Vegetative 23–60 [8]
Maize Reproductive 70–47 [8]
Maize Reproductive 63–88 [67]
Maize Grain filling 79–81 [8]
Sunflower Reproductive 60 [8]
Cowpea Reproductive 60–11 [8]
Soybean Reproductive 46–72 [68]
Barley Seed filling 49–57 [69]
Sunflower Reproductive 60 [8]
Potato Flowering 13 [70]
stage which generally results to reduce yield [63].
In Table 2, yield reduction in crops as a result of
drought stress which depends upon the degree
and period of stress has been reported.
McMaster and Wilhelm 2003 [64] report that
growth period of barley (Hordeum vulgare L.) and
wheat (Triticum aestivum L.) get reduced under
drought stress which ultimately affects yield.
5. BIOTECHNOLOGY METHODS IN
DEVELOPING DROUGHT
TOLERANCE PLANTS
5.1 Use of Classical Breeding
In light of critical global scenarios related to water
availability for agricultural purposes, techniques
such as conventional breeding and marker-
assisted selection are employed to develop
drought tolerance in crop plants for human
consumption [71].
Conventional breeding for developing drought
tolerance in plants involves the art of hybrid
cross to develop new and improved cultivars.
Retrospectively, filed crop breeding approaches
have increased yields through selection and
combination of identifiable characteristics. The
breeding program requires the identification of
genetic variants to drought stress and other
abiotic stress among crop cultivars where the
different genetic traits are introduced into
varieties with the required features [72]. This
method has been used for ages in breeding
programs of cereal crops. Due to the existence of
tolerance variability to a large extent among
plants to environmental stress, the existence of
stress regulatory genes in plants to abiotic and
biotic stress has been long accepted worldwide.
Traditional breeding techniques have
demonstrated the fact that heritable traits
conferring stress tolerance are regulated by a
spectrum of genes expression synergistically,
which may explain why genetic engineering of
plants with drought tolerance are cumbersome
[71]. The expression of single gene encoding
functional proteins like late embryogenesis
abundant proteins, antifreeze proteins, and
molecular chaperones, would normally confer
some level of tolerance to stress but do not
completely give sustained tolerance to the
majority of environmental stresses. Nevertheless,
as the plants develop and evolve, a composite of
molecular interactions may lead to their
sustenance in water limitation alongside other
environmental stresses and in this way, a set of
regulatory genes encoding regulatory proteins
have been established. The expression of
regulatory proteins among others is central to the
expression of genes for defense [73].
Marker-assisted selection is also a technique
used in improving drought stress
tolerance/resistance. In this technique, relevant
quantitative trait locus for drought stress traits
are usually added into plants with high yielding
potential and thus developed mutant enhanced
varieties that have only the major quantitative
trait locus. Commonly known molecular markers
such as random amplified polymorphic DNA
(RAPD) and restriction fragment length
polymorphism has helped to bring about the
development of drought tolerance traits that their
expression is independent of environmental
effects [72].
5.2 Use of Genetic Manipulation
The response of a plant to drought stress has
been studied at different levels such as the
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40
ecological, cellular, physiological and molecular
levels and research in these areas has
established a bone technological basis now in
use for developing plants with drought tolerance
through genetic engineering. The limiting factor
to this novel approach of plant modification for
improvement is the availability of relevant genes
and regulatory elements directly involved in
tolerance to drought stress [71]. Increasing crop
yield and value that are exposed to abiotic stress
requires novel techniques to augment classical
approaches which are often unable to a large
degree prevent damage to a crop [26]. One such
novel approach is genomics where a whole
genome sequence is analyzed to discover novel
and functional genes. Loosely, with the aid of
microarrays, 130 genes that are sensitive and
may respond to drought stress have been
established [74] and these genes are directly or
indirectly involved with transcription modulation,
ion transport, transpiration control, and
carbohydrate metabolism. With the advent of this
technique, genes have been uncovered and
functional genes for stress tolerance are
established [26]. The discovery paves room for
another novel technique known as recombinant
DNA technology where the genetic makeup of
plants can be modified with relevant genes to
tolerate environmental stress. Plant transgenesis
in contrast with conventional breeding
approaches ensures the incorporation of genes
of interest into the target plant. de Campos et al.
reported the transgenic ‘Swingle’ citrumelo
induced with P5CSF129A gene that encode the
key enzyme for proline biosynthesis and
accumulation that is crucial in promoting drought
tolerance in crops with higher osmotic
adjustment [75]. With the era of recombinant
DNA technology, the development of genetically
engineered plants with improved value seems to
be a viable approach of crop improvement in
contrast to classical or marker-assisted breeding
approaches [73]. The development of
transformation methods has resulted in an
efficient generation of genetically modified plants
to sustain crop productivity against abiotic
stresses [76].
5.3 Through the Genes from Resurrection
Plants
Resurrection plants are unique in that they can
survive almost complete dehydration from their
vegetative parts. They shut down their metabolic
systems to tolerate dehydration and the plants
are lifeless [77]. Plants species whose seeds and
vegetative parts can survive severe water loss or
are desiccation-tolerant are regarded as
resurrection plants (poikilohydric), as opposed to
dehydration sensitive plants (homohydric)
[78,79]. Resurrection plants make up an
outstanding group within the flowering plants.
The plants have a unique ability to withstand
thorough dehydration of their vegetative
components [80]. The changes in water levels
and cellular responses associated with
dehydration in seeds are shown to be similar in
resurrection plants that are exposed to metabolic
stresses as a result of severe water loss [81]. For
plants to successfully withstand complete
dehydration needs the concerted expression of
thousands of genes that involved 63 metabolic
pathways and the utilization of 64 biochemical
defense mechanism to protect cellular biological
integrity. The gene family of early light-induced
proteins (ELIPS) is generally over-expressed
during dehydration in all studied resurrection
plants and may play a central role in
safeguarding against photo-oxidative stress of
the photosynthetic machinery during extreme
dehydration [82]. One such dehydration
associated gene (dsp-22) in resurrection plant
Craterostigma plantagineum codes for a mature
21 kDa protein which accumulates in the
vegetative parts and contrasts to other
dehydration associated genes, light is crucial in
regulating the expression level of dsp-22 [83].
Systemic studies of drought stress in the
resurrection plant involve identifying a larger
number of genes, metabolites, and proteins that
usually respond to desiccation or drought stress.
Some of these mechanisms that help cellular
protection during extreme dehydration are
peculiar to desert species [84]. VanBuren et al.
[85] Reported that desiccated plant evolves from
a combination of gene duplications and network-
level rewiring of existing seed desiccation
pathways.
5.4 Through Protoplast Fusion
Protoplasts are cells without cell walls and
cytoplasmic membrane forms the outermost
layer in such cells. They can be obtained through
the activity of some specific lytic enzymes such
as cellulose, pectinase or macerozyme to
degrade cell wall [85]. Through protoplast fusion,
scientists can circumvent mating type and
incompatibility group limit to investigate
mitochondrial genetics, performed inter-generic
protoplast fusion [86]. The fusion of isolated plant
protoplasts by electrical stimulation has been
studied and routinely employed as an
experimental method. Nevertheless, the user of
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41
this method is faced with constraints by the
composition of the suspension medium [87]. The
protoplast fusion technique has remarkable
possibilities for genetic variability and strain
enhancement [88]. Hennig et al. [89] Reported
the use of protoplast fusion lines of poplar
hybrids under drought stress. Protoplast
technology is one of the promising techniques
that can be used by plant breeders to improve
crop varieties [90]. Hawkes [91] Reported the
use of protoplasts fusion to develop drought
tolerance in explant-derived tissue cultures of
Colt cherry (Prunus avium x pseudocerasus)
5.5 In vitro Selection Technique
The in vitro tissue culture approach which
employ the use of a selective medium containing
selective agents to select and improve plants
with specific features. The technique has offer
opportunity to regenerate and induce stress
tolerance in plants through the use of selective
agents such as NaCl, polyethylene glycol or
mannitol, etc which allow preferential growth and
survival of desirable features [92-94]. The
explants are either exposed in a stepwise
manner with gradual increase in the
concentration of the these selecting agents or
are exposed to shock treatment where the
culture medium contain high concentration of the
agents [95]. Plants that survived such
environmental exposure are eventually selected.
These approach induces genetic variation among
the exposed explants in cultured medium and
regenerated plants called somaclonal variation
which can result in genetically stable traits useful
in crop improvement [96,97]. In vitro selection
technique for explants demonstrating increased
drought tolerance has been reported.
Polyethylene glycol (PEG) has been utilized to
induce drought stress in plants and the
determination of plants that withstand water
stress is based on accumulation of consistent
solutes primarily proline as well as the presence
of antioxidative enzymes such as peroxidases,
catalases, and dismutases [95].
6. DISCUSSION
The development of plants with the ability to
establish and withstand/tolerate water limitation
and remain productive in marginal soils is one of
the major goals of crop and forage breeding
programs worldwide [98].
In a world where population growth exceeds food
supply, overcoming environmental stresses that
affect crop yield and quality becomes relevant.
Drought is the most important abiotic stress that
can affect plant growth and development and
efforts have been recorded down the line to
improve crop yield under water–limiting state.
The drought tolerance mechanism is a complex
process that involves a wide range of
physiological, morphological and biochemical
interactions at various levels of plant growth and
development which may include stomatal
regulation, synthesis of osmoprotectants,
generation of osmolytes, reduction in water loss
and increased water uptake, etc. Understanding
the effect of drought stress like other abiotic
stresses becomes relevant to ensure food
supply.
7. CONCLUSION
Plant drought stress is a major problem in the
growth and development of plants. One of the
major challenges of the plant biotechnologist is
solving the problem of plant drought stress so
that it can combat the problem of climatic change
and increase in population growth. Recent
advances in plant biotechnology has seen
remarkable progress in molecular markers
selection processes and in developing transgenic
plants with increased drought stress tolerant.
These approaches have facilitated our
understanding of underlying processes in plant
responses to drought induced stress. Through
plant genetic engineering and molecular marker
techniques, drought stress induced genes have
been identified and cloned.
It therefore means that the applications of
biotechnological and molecular approaches such
as genomics, proteomics, and transcriptomic that
can enhance a better understanding of plant
water use efficiency and tolerance to improve
yield under drought stress is very promising.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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