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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5968_Библиотеки_им_академика_М_И_Перельмана
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affect the cell in various ways, which can affect cell survival. The primary environ-
mental factor that controls PSMs, particularly flavonoids and terpenoids, is temper-
ature. Although a comprehensive mecha nism for SMS accumulation under cold
stress is still unknown. However, cold stress increases the accumulation of
flavonoids and terpenoids in plants in different ways: (1) by increasing the levels
of endogenous plant hormones, such as jasmonic acid and abscisic a
cid; (2) by
altering the expression and activity of key transcription factors, such as the bHLH
and MYB families; and (3) by increasing the activity of enzymes critical to the
biosynthetic pathways of terpenoids and flavonoids; and (4) by post- translational
regulation.
110 C. Singh et al.
7.2.3 Salt Stress
Plants respond to salinity, or salt stress, largely through epigenetic modification. Salt
stress affects DNA methylation and regulates the expression of genes involved in
adaptive responses (Singroha et al.
2022). Histone modifications, such as acetyla-
tion, methylation, and phosphorylation, can also be affected by salt stress. Moreover,
the regulation of gene expression by small RNAs, including microRNAs, is also
affected by salt stress. These epigenetic modifications help plants adapt to salt stress
by providing an efficient mecha nism for altering gene expression without abrupt
changes in underlying gene sequences (Miryeganeh
2021).
7.2.4 Water Deficit Stress
Water deficit stress is a condition in which plants experience a lack of available
water, resulting in decreased growth, an increased risk of disease, and decreased
yields. It can be caused by inadequate rainfall, high temperatures, strong winds, and
evapotranspiration. To minimize the effects of water deficit stress, plants can be
irrigated and mulched, and their roots can be protected from extreme temperatures
and wind. Water scarcity is a major abiotic stressor for plants, with both acute and
chronic consequences. Stomatal closure, changes in ion fluxes, and osmolyte accu-
mulation are the acute effects of a water deficit (Seleiman et al. 2021). However, the
chronic effect of a water deficit leads to epigenetic alterations, such as changes in
DNA methylation and hist one modifications. These epigenetic modifications have
been found to be heritable and may confer increased tolerance to drought-like
conditions (Sun et al. 2021).
7.3 Secondary Metabolites Produced in Plants in Response
to Abiotic Stress
PSMs are the chemical compounds (phenolic compounds, terpenoids, alkaloids, and
flavonoids) produced in plants in response to different stresses, such as temperature,
water, nutrients, pathogen exposure, etc. (Yeshi et al. 2022a) (Fig. 7.1) (Table 7.1).
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7 Revealing the Epigenetic Mechanisms Underlying the Stress Response... 111
Fig. 7.1 Factors affecting epigenetic change in plants resulting from altered secondary metabolite production
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Plant Heritable Reference
––
––
Phenolic compounds are produced by exposure to low temperatures, intense light,
and drought conditions, whereas terpenoids are produced by exposure to ultraviolet
radiation, high salinity, and pathogen attack. Alkaloids are produced in response to
high temperatures, drought, and a lack of nutrients, whereas flavonoids are produced
in response to UV radiation, high salinity, and pathogen attack (Yang et al. 2018;
Zhan et al.
2022). These secondary metabolites help plants defend themselves
against environmental stress, protect them from pests and diseases, and aid in the
uptake of nutrients (Borges et al.
2017). Secondary metabolites protect plants by
acting as herbivore deterrents, pathogen barriers, and oxidative stress mitigators.
Different abiotic factors, such as light, temperature, soil water, and salt stress, have a
strong influence on the accumulation of SMs. Even if other environmental
conditions stay constant, a change in one en vironmental component can alter the
concentration of secondary metabolites in most plants. Abiotic stress-affected plants
could be
a potential alternate source for drug discovery. Plants secrete a variety of
PSMs to protect themselves against cell and tissue damage. Plants can eith er create
novel molecules or elevate the levels of already existing compounds (Yeshi et al.
2022b) (Table 7.2).
112 C. Singh et al.
Table 7.1 Epigenetic studies conducted on medicinal plants
Epigenetic
modification
Environmental
parameter
Medicinal
uses
Taraxacum
officinale
DNA
methylation
Salt stress, low
nutrients, JA
application, SA
application
Yes Anti-
inflammatory
Jeon et al.
(
2008),
Verhoeven
et al. (
2010)
Pinus pinea DNA
methylation
Antioxidant,
antibacterial
Ulukanli
et al. (
2014),
Saez-Laguna
et al. (2014)
Ilex
aquifolium
DNA
methylation
Herbivory – Antioxidant Nahar et al.
(
2005),
Herrera and
Bazaga
(
2008)
Viola
cazorlensis
DNA
methylation
Herrera and
Bazaga
(
2010)
Alternanthera
philoxeroides
DNA
methylation
Water
availability
– Antiviral Nahar et al.
(
2022), Gao
et al. (
2010)
Dactylorhiza
species
DNA
methylation
Water and
temperature
– Dysentery,
diarrhea
Dorjey et al.
(
2022), Paun
et al. (
2010)
Eucalyptus
nitens
DNA
methylation
– Yes
Antioxidant Thumma
et al.
(
2009)
Abioti
c
stress
is
a
maj
or
factor
that
affects
the
production
of
PSMs
(Isah 2019).
These
stresses
can
alte
r
the
product
ion
of
PSMs
in
plants,
which
can
lead
to
changes
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SM Name Class
Reference
in the amount and type of PSMs produced. These changes may lead to altered levels
of protective compounds or compounds with medicinal or nutritional value. Under-
standing the effects of abiotic stress on the production of PSMs can help researchers
better understand how plants adapt to their environment and identify potential
strategies for improving the production of useful compounds. The twentieth century
saw an increase in global temperature of 0.47 °C, leading to a
significant impact on
PSMs production as both high and low temperatures affect plant survival. The plants
cope with heat stresses by enhancing the production of SMs (Karwasara and Dixit
2013). The production of SMs in plants is also affected by the quality of light, such
as photoperiod and intensity (Carvalho et al.
2011).
7 Revealing the Epigenetic Mechanisms Underlying the Stress Response... 113
Table 7.2 Secondary metabolites and their biological activity in various plant species
Plant
Terpenes
Biological
activity
Tanshinone Cannabinoid Salvia
miltiorrhiza
Salt stress Yu et al.
(
2021)
Artemisinin Sesquiterpenes Artemisia
annua L.
Arsenic stress Kumari et al.
(
2018)
Limnoids Triterpenes Citrus fruits Antiherbivore Yu et al.
(
2005)
α-Pinene/β-pinene Monoterpenes Oryza sativa Allelopathy Chen et al.
(
2022), Kaur
et al. (
2022)
Phenolic compounds
Kaempferol Flavonoids Arabidopsis
thaliabna
Oxidative
stress
Likić et al.
(
2014)
Daidzein Flavonoids Glycine max Oxidative
stress
Manikonda
et al. (
2009)
Oleuropein Polyphenolic Olea
europaea
Salt stress Mechri et al.
(
2019)
Quercetin Arabidopsis
thaliabna
Oxidative
stress
Kurepa et al.
(
2016)
Nitrogen-containing SMs
Citrulline Cyanogenicglucoside Sorghum
bicolor L.
Osmotic stress Song et al.
(
2020)
Dhurrin Nonprotein amino
acids
Calliandra
sp.
Antiherbivores O'Donnell
et al. (
2013)
The effects of radiation on PSMs can be either positive or negative, depending on
the type an d intensity of radiation exposure. Exposure to light can trigger the
production of flavonoids and carotenoids, in plants. Light is also necessary for
photosynthesis, which is the process by which plants produce energy and other
essential compounds. UV radiation can be harmful to plants, as it can damage the
photosynthetic machinery and reduce the production of secondary metabolites.
However, some plants have evolved to use UV radiation to their advantage. For
example, certain species of plants can use UV radiation to produce photoprotective
secondary metabolites, such as flavonoids, that can protect them from UV damage.
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Ionizing radiation, such as gamma and X-rays, can be damaging to plants, as it can
damage and destabilize the genetic material. This can lead to mutations as well as the
production of SMS.
114 C. Singh et al.
7.4 Pharmacological Properties of Secondary Metabolites
SMs produced in plants in response to different abiotic stresses have different
pharmacological properties, such as antioxidant, anti-inflammatory, neuroprotective,
cytotoxic, antimicrobial, cardioprotective, etc.
7.4.1 Antioxidant Activity
Secondary metabolites play a crucial role in plant defense and their production can
affect a plant’s antioxidant activity. Secondary metabolites can act as antioxidants
themselves, with some compounds, like flavonoids, being particularly effective at
scavenging reactive oxygen species. Additionally, the production of SMs can
enhance the expression of antioxidant enzymes, such as superoxide dismutase
(SOD) and catalase, which then work to prevent cellular damage caused by oxidative
stress.
7.4.2 Anti-Inflammatory Activity
Secondary metabolites can reduce the inflammation caused by environmental
stressors. Many SMs have been found to possess anti-inflammatory activity, which
means they can help reduce inflammation in the body. This anti-inflammatory
activity can be altered by changes in the production of SMs, induced due to genetic
alterations or environmental stimuli (Lee et al.
2013). For example, some plant
species produce increased amounts of certain secondary metabolites when exposed
to certain environmental stressors, such as drought or cold. This can lead to an
increase in the anti-inflammatory activity of these compounds. Similarly, genetic
modifications lead to changes in SM production, which can alter the anti-
inflammatory activity of the plant (Kowalczyk et al. 2020).
7.4.3 Antimicrobial Activity
PSMs prevent infections by inhibiting the growth of microorganisms. The antimi-
crobial activity of secondary metabolites can be enhanced by altering their structure
and/or concentration or by combining them with other compounds (Allemailem
2021; Othman et al. 2019). This could be done through genetic modification or the
selection of suitable plant varieties with higher levels of these compounds. Another
method of increasing the antimicrobial potential of SMs is through the selection of
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suitable plant varieties that naturally produce higher levels of these compounds. This
can be done through conventional breeding or the use of advanced technologies,
such as genome editing. For example, researchers have used CRISPR-Cas9 technol-
ogy to modify the genome of tomatoes to increase their production of lycopene,
which is a secondary metabolite with strong antimicrobial properties (Li et al.
2018).
7 Revealing the Epigenetic Mechanisms Underlying the Stress Response... 115
7.4.4 Cytotoxic Activity
The cytotoxic activity of secondary metabolites is useful in the treatment of certain
diseases. This cytotoxic activity can be caused by a variety of compounds, including
terpenoids, alkaloids, phenols, and others (Seca and Pinto 2018). Depending on the
plant and its environment, the types of secondary metabolites produced can vary, as
can their corresponding cytotoxic activity. For example, some plants produce
terpenoids that contain aldehy de and ketone groups, which can be very toxic to
other organisms. Similarly, alkaloids, such as nicotine and caffeine, can also be
toxic, depending on their concentration. In some cases, the cytotoxic activity can be
used to defend the plant from pests and pathogens and can also be beneficial for
humans, providing us with novel drugs and other therapeutic compounds.
7.4.5 Neuroprotective Activity
Secondary metabolites can protect the brain and nervous system from damage
caused by environmental stressors. It is believed that certain compounds found in
plants, such as polyphenols and flavonoids, possess neuroprotective properties and
can act as antioxidants, anti-inflammatory agents, and anti-apoptotic agents (Kumar
and Khanum
2012). These compounds can help protect neurons from free radical-
induced damage, inflammation, and apoptosis and reduce the risk of developing
neurodegenerative diseases (Ataie et al.
2016). Additionally, some plant-derived
compounds have also been found to promote nerve growth and regeneration, as well
as improve cognitive performance.
7.4.6 Cardioprotective Activity
Secondary metabolites can protect the heart and circulatory system from damage
caused by environmental stressors. The cardioprotective activity of PSMs is a result
of their ability to modulate multiple cellular pathways involved in cardiovascular
health. PSMs can also inhibit the growth of cardiovascular disease-causing bacteria
and viruses (Ramírez-Rendon et al. 2022). Additionally, they can protect the heart
from the effects of oxidative stress, reduce platelet aggregation, and promote vaso-
dilation (Kibel et al. 2020). PSMs can help reduce the risk of developing cardiovas-
cular disease by modulating different pathways. Prior studies reported that these
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compounds can protect the heart from the effects of oxidative stress, reduce platelet
aggregation, and promote vasodilation.
116 C. Singh et al.
7.5 Epigenetic Responses against Stresses
Epigenetic responses are the stress-induced alterations in gene expression that occur
without underlying DNA sequence changes. These epigenetic responses can alter the
expression of genes by modifying DNA or histone proteins (Kumari et al.
2022).
These epigenetic alterations regulate growth, flowering, and stress responses. Addi-
tionally, they can affect how an organism reacts to environmental elements like
temperature and nutrient availabil ity. In addition, epigenetic changes can change the
way cells respond to future stressors, making them more or less susceptible to certain
diseases. Thus, understanding how epigenetic responses to stressors can shape health
outcomes is an important area of research (Miryeganeh 2021). The epigenetic
regulation occurs through DNA methylation, histone modification, and small
RNAs (Fig.
7.2).
Fig. 7.2 Mechanism of epigenetic modification in plants
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7 Revealing the Epigenetic Mechanisms Underlying the Stress Response... 117
7.5.1 Epigenetic Regulation by DNA Methylation
Genome modification is critical for adapting microorganisms to environmental
stresses. This involves the manipulation of the DNA, RNA, and histone proteins
of the chromatin. These processes regulate the functioning of genes, which control
the different metabolic processes of the organism. To change the expression of genes
without changing the underlying DNA sequence, in epigenetic alterations, the
expression of a gene is changed by methylation of particular bases without changing
the underlying DNA sequence, histone modification, chromatin remodeling, or
transcriptional regulation. These epigenetic alterations can be passed down through
the generations and can affect how organisms develop and work. Additionally, DNA
methylation can influence the stability of epigen etic marks and the formation of
chromatin structures, which can further affect gene expression.
7.5.2 Mechanism of DNA Methylation
DNA replication is made easier by the symmetry of CpG and CpNpG methylation;
in contrast, every DNA replication set containing non-symmetrical CpNpN methyl-
ation requires a subsequent de novo methylation (Wada et al.
2003). It was discov-
ered that almost the majority of methylation takes place at CpG sit es, although a
sizeable portion also happens at non-CpG locations (Moore et al. 2013). Every time
a DNA duplication cycle occurs, the newly formed, unmethylated strand produces a
hemimethylated medium, which attracts MET1 and methylates the unmethylated
CG region (Gouil and Baulcombe
2016). CHH methylation is a complex process
involving two distinct mechanisms. Transposable elements, found in heterochroma-
tin, are produced by CMT2 and contain H3K9me2 (Zhang et al.
2018
). In euchro-
matic regions, a self-reinforcing loop is triggered by 24-nucleotide siRNAs that
direct de novo methyl-transferase to modify the sequence. This process is carried out
by several DNA methyltransferases, depending on the sequence’s content. Once
established, MET1 and CMT3 continue to maintain the methylation. DNA demeth-
ylation can be achieved passively by diluting the methylation scripts through DNA
duplication. Contrary to initial speculation, 5-methylcytosine does not directly
convert to cytosine. On the other hand, active DNA methylation entails the deami-
nation of the methylated base or the oxidation of the methylated base via 10 to
11 translocations. The BER corridor replaces the modified nucleotide, sometimes
together with adjacent nucleotides. A fresh detail highlighted the function of well-
known enzymes in this process. They are aware that , in addition to BER, other DNA
destruction repair channels can be involved in the active demethylation of DNA,
such as base editing repair glycosylases, which can work in conjunction with or
instead of thymine DNA glycosylase during the base removal stage (Bochtler et al.
2017).
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118 C. Singh et al.
7.5.3 RNA-Mediated DNA Methylation
RNA molecules of varying sizes play a significant role in controlling the expression
of genes, preserving genome integrity, and helping to defend agains t foreign genetic
materials (Holoch and Moazed
2015). In plants, the process of RNA-directed DNA
methylation regulates denovo-DNA methylation and gene silencing (transcriptional)
through the use of SiRNAs (24 nucleotides) and long non-coding RNAs (Kovalchuk
2021).
Salvia miltiorrhiza is used in traditional Chinese medicine. The 11SmAGO genes
discovered by Saho et al. are responsible for the regulation of the expression and
activity of enzymes involved in the biosynthesis of the active components. The
findings of this study can provide a bett er understanding of the molecular
mechanisms underlying the medicinal properties of Salvia miltiorrhiza and aid in
the development of more effective treatments for various conditions (Shao and Lu
2013).
7.5.4 Epigenetic Regulation by Histone Modification
Histone modification is a process by which the post-translational modification of
histone proteins affects gene expression. Histone modifications are mediated by
enzymes that add or remove chemical tags, such as methyl groups, acetyl groups,
and phosphorylation, to specific sites on the histone tails. These modifications can
either be repressive or activating, depending on the type of modification. For
example, methylation of histones can lead to gene repression, while acetylation of
histones can lead to gene activation. By modulating gene expression, histone
processes, including development, cell cycle progression, and stress responses.
In medicinal plants, histone modifications can be used to regulate gene expression
and, in turn, affect the production of various compounds with medicinal properties.
For example, histone modifications have been used to upregulate the expression of
genes involved in the production of secondary metabolites, such as flavonoids and
alkaloids, which have various medicinal properties. Histone modifications have also
been used to alter the structure and expression of genes involved in the production of
terpenoids, which can be used in the production of drugs with anti-inflammatory and
anti-cancer properties.
7.6 Conclusions
Epigenetics plays a significant role in the response of plants to environmental
stresses and is an important tool for traditional medicine. It is also a driving force
in evolution, helping plants quickly adapt to changing conditions. Epigenetics is an
important and emerging field of research with broad implications for plant biology,
evolution, and traditional medicine. By studying epigenetic modifications,
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researchers can gain a better understanding of the effects of environmental factors on
gene expression. Additionally, epigenetics provides evidence in favor of the idea that
traditional medicinal plants can be used. It can also be concluded that innovative and
adaptable agronomical strategies are essential to meeting the rising medicine
demand brought on by a growing population. Through the use of methyltransferases,
epigenetic markers can be selectively added or
deleted from DNA, allowing for the
combination of herbs and fruits used in traditional medicine to be used in the
treatment of ailments. This has recently brought epigenetics to the field of traditional
medicine, suggesting that it may have a role in the modern-day pharmacology of
traditional medicine prescriptions.
7 Revealing the Epigenetic Mechanisms Underlying the Stress Response... 119
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