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Adaptation of plants to environmental stress conditions

Conference Paper · March 2020

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 CONTENTS
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1. FULL-TEXT PAPERS 1

1.1. ORAL PRESENTATIONS 1

1.2. POSTER PRESENTATIONS 879

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 Adaptation of plants to environmental stress conditions
Radia ABDOURAHMAN1* 2

1*
2

Turkey

Corresponding author e-mail: diaabdi@hotmail.com

Abstract: The main point of this study is to evaluate the mechanisms of adapation of plant to environmental
stresses. Environmental stress conditions are defined as abiotic stresses such as, drought, high soil salinity,
heat, cold, oxidative stress and heavy metal toxicity are the common adverse environmental conditions. Those
influencing stresses are the already present growth parameters in the environment that changed into a harmful
way. Vegetables are grown world-wide in almost 200 countries. A world vegetable survey indicated 392
vegetable crops cultivated worldwide. Plants are fixed living organisms and thus their chance to immigrate
whenever the weather, the soil or the air quality are not good is inexistent; due to that property vegetables
always tend to adapt their organisms to the given environmental situation by resisting the effects of the stress.
Unfortunately not all plants can win against all stress so they are called susceptible plants and die even sooner
than expected. Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen;
ROS has changed because they also participate in developmental processes of plants by acting as signaling
molecules when the plant is exposed to an abiotic or biotic stress. But if their amount in the plant surpasses a
certain amount they become very toxic for the plant and may even lead to their destruction. Plants are very
clever living organisms and always respond to disadvantageous conditions by first using physicals barriers if
not enough they express concerned genes and synthesize defensive chemicals in order to survive.Knowing that
plants have always been widely used by humans, first as nutritive sources, but also as materials, decorative
objects and for their effects (toxic or beneficial) on th
Co2 pollution problems, by supplying oxygen and absorbing CO2 which explains the importance of large
forests, especially tropical.
Keywords: abiotic stress, adaptation, resistance, susceptible, reactive oxygen species.

INTRODUCTION
As sessile organisms, plants are continually exposed to disadvantageous environmental conditions of varying
intensity and scales, including attack by pathogens, wounding by insects which is defined as biotic stress or
exposure to ultraviolet radiation, and decrease in water and nutrient availability, a high concentration of salt
and a very high or low temperatures that are considered as abiotic stress. It is very remarkable that despite the
instability of their environment plants are able to adapt, overcome, and continue to grow, develop, and most
importantly remain productive (Wang 2016). World population is growing at a very alarming rate and for
2030, the UN announces a World population of 8.5 billion which should stabilize at 11.5 billion inhabitants
(Anonymous, 2015) On the other hand, agricultural productivity is not increasing at a required or necessary
rate to keep up with the food demand. The reasons for this are water shortages, dying and not low quality soil
fertility and mainly various abiotic stresses (Venkateswarlu and Shanker, 2011). Optimal growth conditions
are a fundamental and obligatory principle in biology since living organisms cannot control environmental
conditions, they were forced to evolve and cope with the instability of the present environmental growth
conditions. In order to avoid further potentially injurious strains, plants adopted two major strategies for
surviving adverse environmental conditions; stress avoidance or stress tolerance. The avoidance mechanism is
mostly observed in the kingdom of animals, when they simply emigrate from the region of stressful stimuli.

complex biochemical, molecular and genetic mechanisms to avoid stress; else ways, tolerance mechanisms
mainly involve biochemical and metabolic functions which are in turn regulated by genes. Understanding plant
responses to abiotic stresses is crucial because this is the mandatory for developing approaches and tools to
improve plant stress tolerance.
 Figure 1. Biotic and abiotic stresses.

Effects of abiotic factors to plants

Gathered fruits and vegetables can be potentially exposed to numerous abiotic stresses during production,
handling, storage and distribution (Hodges, 2003). Some of these stresses can meaningless and not alarming,
resulting in no quality or productivity loss, in some cases, in quality improvement (Hodges et al., 2005) during
distribution. However, when the abiotic stress is moderate or severe scale, quality and crop productivity losses
almost always are incurred (Toivonen, 2003a; Toivonen, 2003b). It is primordial to understand the relationship
between preharvest (before the gathering of the ripen crops)
and postharvest (after the harvest of ripen crops) abiotic stresses that the fruit or vegetable is exposed after
harvest and during storage and distribution, since the solution to these different problems will be best resolved
by focusing on preharvest or postharvest abiotic stress amelioration, respectively. Moderate levels of
preharvest stress can potentially work towards enhancing stress resistance of a fruit or vegetable through up-
regulating genes and pathways which renders the tissues cross-tolerant to many stresses (Lesham and Kuiper,
1996; Bowler and Fluhr, 2000) which may occur subsequently in postharvest handling, storage and
distribution. Drought, plant nutrition, extreme temperatures, salinity and light are the widely occurring
preharvest abiotic stresses; extremes temperatures, low O2 and high CO2, desiccation are the known postharvest
stresses (Venkateswarlu and Shanker, 2011).

Effects of drought

The occurrence of drought stress during production of plants is becoming more frequent with climate change
year after year (Whitmore, 2000). Drought is the absence of rainfall or supplemental irrigation for a period of
time sufficient to deplete soil moisture, resource of groundwater and injure plants. Drought stress is observed

water content is reduced enough to interfere with normal plant processes. As we know water is a very important
biological component that plays an important role in the realisation of very vital biochemical processes .
CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage due to heat that comes
along the dry and disturbed activity of various enzymes that demand optimal temperature in order to function,
especially those of CO2 fixation and transportable energy synthesis. Drought stress decreases CO2 assimilation
rates due to reduced stomatal conductance. It reduces leaf size, stems extension and root proliferation, disturbs
plant water relations and reduces water-use efficiency. It disrupts photosynthetic pigments and reduces the gas
exchange leading to a reduction in plant growth and productivity. Pushes metabolite flux through the
photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen
species which are cytotoxic elements and inhibits photosynthesis. Injury caused by reactive oxygen species to
biological macromolecules under drought stress is among the major deterrents to growth (Farooq et al., 2009).
Under environmental stresses such as drought, a rapid ROS accumulation including singlet oxygen (O 2 ),
superoxide ( O2), hydroxyl (OH ) and hydrogen peroxide (H2O2) may occur, leading to negative impact on
antioxidant metabolism, and consequently cell peroxidation damage (Smirnoff, 1993).
Mechanism of resistance to drought

Drought triggers a wide variety of plant responses, ranging from cellular metabolism to changes in growth
rates; aspects of drought induced changes are morphological, physiological and biochemical changes in
plants. During prolonged water stress plants must be able to survive with low water content and maintain a
minimum amount of water, through water uptake and retention. To cope with prolonged drought stress plants
respond with energy demanding processes that alter the growth pattern, chemical content of the plants and
the up or down regulation of genes; when plants suddenly encounter drought it is important to respond as
quickly as possible. A faster drought response means that less water is lost and the survival rate of the plants
is increased.

Long term response

Biochemical and growth changes occur in long term response, when the water availability is reduced in long
term, plants change their biochemistry to be able to sustain as much water as possible and take up whatever
water they can. During water stress plants produce and accumulate compatible solutes or Osmoprotectants
they are small organic molecules with neutral charge and low toxicity at high concentrations that act as
osmolytes and help organisms survive extreme osmotic stress such as sugars, polyols and amino acid to lower
the osmotic potential in the cells to facilitate water absorption, uptake and retention (Xiong and Zhu, 2002).
Some of the compatible solutes also contribute to maintaining the conformation of macromolecules by
preventing misfolding or denaturation (Xiong and Zhu, 2002). A group of proteins called late embryogenesis
abundant like (LEA) proteins are also produced during water stress. These LEA-like proteins are highly
hydrophilic and highly soluble and have been found to be regulated by ABA (Xiong and Zhu, 2002). The LEA-
like proteins are thought to act as chaperones, protecting enzymatic activities (Reyes et al., 2005) and
preventing misfolding and denaturation of important proteins (Xiong and Zhu, 2002). Some of the LEA-like
proteins have similar features as ribosomal proteins and are thought to interact with RNA (Garay-Arroyo et
al., 2000). Many antioxidant systems, both enzymatic and non-enzymatic, are up-regulated in response to the
increased reactive oxygen species levels during water stress. These antioxidants scavenge the reactive oxygen
species and reduce the oxidative damage. The enzymatic antioxidants, such as superoxide dismutase,
peroxidase, ascorbate peroxidase, catalase, polyphenol oxidase and glutathione reductase can detoxify reactive
oxygen species (Prochazkova et al., 2001; Jaleel et al., 2009b). Drought causes cells to lose turgor pressure
and shrink, the loss of turgor pressure in the cells inhibits turgor dependent activities such as cell expansion,
which affects the growth of the whole plant. Some studies show that ABA can function as a signal to reduce
leaf growth. In some cases drought can lead to the abscission of leafs in order to lessen the water lose surface
and increase the root growth and by that teh area of water uptake become larger and deeper water resource can
be attained.

Short term response

A faster drought response means that less water is lost and the survival rate of the plants is increased. The most
important quick response is stomatal closure. Stomata consist of two guard cells surrounding the stomatal pore.
When the stomata are open water is transpired and CO2 enter the leaf through the stomatal pore. During water
stress the stomatal pore can be closed to reduce water loss. By closing the stomatal pore the water use efficiency
is increased (Farooq et al., 2009).
 Figure 2. Plant responses to water stress

Effect of extreme temperature

Temperature is one of the main factors affecting the rate of plant development and crop productivity today as
the climate change is getting more and more unpredictable. Every kind of plant species requests their own
optimal and favorable temperature for their very ongoing biochemical ad vital processes. High temperature
and low temperature have different effects on plant ant their growth but according to the plant species, whether
yes or not the plant is resi
temperatures; the effects as well as the plant responses are going to remain different. High light and heat stress
most commonly come across a plant simultaneously since their occurrence require the same kind of
environment, heated and dry with heavy sun lights, they both cause denaturation of vital biologic components,
membrane damages and photorespiration that leads to ROS accumulation, apparition of necrosis, apparition of
dark spot on leaves and stems, diminution of the amount of Nitrate Reductase enzyme in the roots; seed
germinations are also inhibited. Cold or freezing stress is the result of very low temperatures that goes under
0o nsform into its solid for by condensation while forming crystals that gets
bigger and larger, those crystals cause growth inhibition, negatively affects plasma and membrane properties,
dehydration and frost that damages the plant. Living organisms can be classified into three groups, subject to
the preferred temperature of growth (Figure 3). There are (a) Psychrophilic: which grow optimally at low

10 a

Plant response to heat stress

Under heat stress conditions, plants evolve multiple mechanisms for surviving which include long-term
adaptations and short-term avoidance. Long-term adaptation or tolerance are heritable modification to increase
-term response are very temporary non-heritable physiological and biochemical gene
expression. Avoidance mechanisms include processes such as changing leaf orientation, transpirational
cooling, or alteration of membrane lipid compositions. Closure of stomata and reduced water loss, increased
stomatal and trichomatous densities, and larger xylem vessels are common heat induced features in plant
(Srivastava et al., 2012). Plants growing in a hot climate avoid heat stress by reducing the absorption of solar
radiation. This ability is supported by the presence of small hairs (tomentose) that form a thick coat on the
surface of the leaf as well as cuticles, protective waxy covering and reflecting the surplus and harmful light
amount. In such plants, leaf blades often turn away from light and orient themselves parallel to sun rays
(paraheliotropism); Solar radiation may also be reduced by rolling leaf lamina and decreasing the absorption
area. When a plant uses the avoidance response her ultimate objective is to inhibit growth and focus more on
the defensive matters while heat tolerance is generally defined as the ability of the plant to grow and produce
economic yield under high temperature. They include short term avoidance/acclimation mechanism or long
term evolutionary adaptations. Some major tolerance mechanisms, including ion transporters, late
embryogenesis abundant (LEA) proteins, osmoprotectants, antioxidant defense, and factors involved in
signaling cascades and transcriptional control are essentially significant to counteract the stress effects
(Rodrigez et al., 2005).

Plant response to cold stress

The expression of cold-responsive genes is induced during cold exposure. During this process, plants increase
their tolerance to cold stress by synthesizing numerous protective substances (e.g. soluble sugars, proline) and
proteins (e.g. LEA, AFP, CSP), Soluble sugars, prol
osmolytes to protect plants from damage caused by cold stress (Ruelland et al., 2009). The accumulation of

PROTEINS (AFPs) and COLD SHOCK PROTEINS (CSPs) during cold acclimation is important for freezing
tolerance in plants (Ruelland et al., 2009). Several other LEA proteins were identified in different plant
species, and proved that they are important factors in regulating plant chilling or freezing tolerance
(Houde et al., 2004; Qiu et al., 2014; Sasaki et al., 2014; Liu et al., 2015).

Figure 3. Fundamental response of plant to cold stress

Effects of salinity stress

Salinity is one of the most serious factors limiting the productivity of agricultural crops, with adverse effects
on germination, plant vigour and crop yield (Munns and Tester, 2008), major processes such as photosynthesis,
protein synthesis and energy and lipid metabolism are affected; high salinity affects plants in two main ways:
high concentrations of salts in the soil decreases the capacity of roots to extract water, and high concentrations
of salts within the plant itself can be toxic, leading to the inhibition of many physiological and biochemical
processes such as nutrient uptake and assimilation (Hasegawa, et al., 2000; Munns, 2002; Munns, et al., 1995;
Munns and Tester, 2008). When plant are present in favourable environmental conditions the water potential
of the plant is higher than the potential hydrique of the soil which let the plant easily pump water from the soil
but once the soil salinity increase they tend to restrain the uptake capacity of roots to uptake the quantity of
necessary water. Thus salt stress causes osmotic and ionic disturbs which leads to ROS production and
accumulation and decreases nutritive mineral uptake by the pant. The salt-induced inhibition of the uptake of
important mineral nutrients, such as K+ and Ca2+, further reduces root cell growth (Larcher, 1980). Na+
accumulation turns out to be toxic especially in old leaves, which are no longer expanding and so no longer
diluting the salt arriving in them as young growing leaves do. If the rate at which they die is greater than the
rate at which new leaves are produced, the photosynthetic capacity of the plant will no longer be able to supply
the carbohydrate requirement of the young leaves, which further reduces their growth rate (Munns and Tester,
2008). In photosynthetic tissues, in fact, Na+ accumulation affects photosynthetic components such as
enzymes, chlorophylls, and carotenoids (Davenport et al., 2005).

Salt tolerance

The mechanisms of genetic control of salt tolerance in plants have not yet fully understood because of its
complexity, given this situation elaborate explanations will be very hard to be proposed but we will try to
apprehend the mechanisms that plants actives when exposed to high salinity. Osmotic tolerance is a path of
ought aspect of salinity stress and to maintain leaf
expansion with their turgor and stomatal conductance (Rajendran et al., 2009). It was demonstrated in a study
of genetic variation in tolerance to osmotic stress. Another essential mechanism of tolerance involves the
ability to reduce the ionic stress on the plant by minimizing the amount of Na+ that accumulates in the cytosol
of cells, particularly those in the transpiring leaves. This process involves up and down regulation of the
expression of specific ion channels and transporters, allowing the control of Na+ transport throughout the plant
(Munns and Tester, 2008; Rajendran et al., 2009). Separately stockage of Na + and Cl at the cellular and
intracellular level to avoid toxic concentrations within the cytoplasm is also a mechanism of tolerance,
especially in mesophyll cells in the leaf (Munns and Tester, 2008) and synthesis and accumulation of
compatible solutes hin the cytoplasm. Compatible solutes or osmoprotectants play a role in plant
osmotolerance by various ways, protecting enzymes from denaturation, stabilizing membrane or
macromolecules or playing adaptive roles in mediating osmotic adjustment (Ashraf and Foolad, 2007).

Figure 4. Chemical structures of some important osmoprotectants

RESULTS AND DISCUSSION

Unlike animals plants are sessile living be

whenever a lethal stress condition occurs. According to many proprieties such as the concerning species, its
aptitude to cope with certain extreme environmental factors, stress effect and the plant response will be
different. Some plants are halophyte while others are glycophytes, high salinity will cause toxic effects to the
glycophytes plants while halophyte plants keep their growth rate increasing, in the other way halophyte plants
will struggle in soil with low salt concentration while glycophyte plants will find their optimum conditions.
The same logic goes for the rest of abiotic stresses. Some species are naturally resistance while other avoids
any growth process while being confronted to stresses; susceptible plants rather die due to lack of responses
mechanisms. Abiotic stresses are significant determinants of quality and nutritional value of fruits and
vegetables during harvest, handling, storage and distribution to consumer. Further research is required to
determine the key genes and molecular pathways that underpin the best tolerance responses crop genotypes to
the common abiotic stresses. Important are the mechanisms that control water loss, high temperature and
elevated salinity. This ability is especially important during stress confrontation, when loss of water can have
serious consequences for the plants. Water stress can cause reduced growth and in severe cases plant death.
To minimize the negative effects of water stress the plants respond by changing their growth pattern, producing
stress proteins and chaperones, up-regulation of anti-oxidants, accumulation of compatible solutes, increasing
the amount of transporters involved in water and ion uptake and transport and by closing the stomata. Stress
signalization pathways which involve ROS envolment lead to stress-responsive gene expression and
physiological changes that gave to the plant tolerance aspect.

CONCLUSION
The development and survival of all living things relies on the ability of organisms to perceive and respond
to their environment. Responses to internal and external signals are frequently elicited by hormones,
receptors and facteurs of transcription through a complex pathway of transductible signals. Once the signal is
set out on to path of the nucleus, defensive responsible genes are then expressed with high rates and genes
that are rather coding for not defensive purposes see their expression decreasing. As plants are exposed to
diverse stresses their ability to overcome it gives to human being hope that even with the ever-changing
climate there is always a solution for a stress effects and by that exposing to elite crops controllable stress
effects will be benefic for plants to even evolve and be more prepared in the future; plant breeding which is
the purposeful manipulation of plant species in order to create desired genotypes and phenotypes for specific
purposes. This manipulation involves either controlled pollination, genetic engineering, developing hybrid
species can be the solution for the distribution and propagation of the newly developed and wanted resistance
characters.

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