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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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and accumulation of free radicals, damage to membranes and proteins (Farsaraei
et al. 2020a), and collapsed plant antioxidant systems, which are carried out by
antioxidant enzymes and secondary metabolites, in addition to reducing EO yield
(Cheng et al.
2018; Selmar and Kleinwächter 2013).
48 T. B. dos Santos et al.
4.4 Salt Stress in Medicinal Plants
Despite the importance, two events can cause soil salinization: the first would be
natural causes, and the second would be inadequate management resulting from
poorly executed irrigation projects (dos Santos et al.
2022a; Bonacina et al. 2022a).
According to FAO (2015 ), primary salinization occupies 1 billion hectares on the
globe, and secondary salinization occupies 77 million hectares. Salinization is
typically associated with arid and semi-arid areas, can be exacerbated by climate
change, and is mainly due to the accumulation of sodium, potassium, nitrate,
phosphate, magnesium, and chlorine ions, among others (Bonacina et al.
2022b).
Depending on the degree and exposure, the most common symptoms observed in
medicinal plants were reduced biomass, changes in the root system and leaf burns,
and changes in stomata conformation and density (Bonacina et al.
2017, 2022b),
reduced absorption of calcium and potassium in leaves, accumulation of sodium ions
(Yu et al. 2015; Bistgani et al. 2019b), metabolic disorders, and changes in EO yield
and composition (Bonacina et al.
2017; Ahmadi et al. 2022).
Additionally, Bonacina et al. (2017) reported for Melissa officinalis L. that the
edges of the leaves were burned from the concentration of 150 mM of NaCl, and a
reduction of 13.20% in the production of EO was visible. Similar symptoms were
also observed in the leaves of Curcuma longa L. (150 mM of NaCl), with an increase
in the number of hypodermic cells being reported in the leaves with a decrease in the
total thickness of the leaf blade, especially of the parenchymal tissue (Bonacina et al.
2022b). Leaf necrosis was also reported by Ahmadi et al. (2022) as the main
symptom caused by excess NaCl in Echinacea purpurea L. In M. canadensis L.,
the symptoms were more drastic in the aerial part of the root system; there was a 70%
reduction in the size of branches from 150 mM of NaCl (Yu et al.
2015).
In Ocimum basilicum L., at a concentration of 120 mM of NaCl, it was observed
that they reduced the biomass, the water content, and the potassium/sodium ratio in
the leaves; on the other hand, an increase in the permeability of the membrane and
the levels of malondialdehyde (MDA) was observed (Farsaraei et al.
2020b). In
Thymus vulgaris and T. daenensis, starting at 30 mM of NaCl, there was a drop in
chlorophyll a and b contents (Bistgani et al. 2019b). In addition, photosynthetic rate,
CO
2
concentration, and stomatal conductance decreased in Mentha spicata
L. exposed to 150 mM of NaCl (Chrysargyris et al.
2019).
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4 Resilience Mechanism of Medicinal Plants Under Harsh Environment 49
4.5 Heavy Metal Stress in Medicinal Plants
Contamination by heavy metals in medicinal plants is another abiotic stress that has
worsened in recent decades. It occurs through human anthropic action and can be
local or diffuse, usually caused by intensive industrial activities, inadequate disposal
of waste, mining, and activities or accidents that introduce excessive amounts of
contaminants (FAO
2015; Lajayer et al. 2017). Many medicinal plants can absorb
heavy metals and be used for phytoremediation; on the other hand, it can prove to be
dangerous when plants are consumed as food, in traditional medicine, or as raw
materials for drugs and cosmetics (Lajayer et al.
2017). Barthwal et al. (2008) carried
out collections of five species of medicinal plants and soil in an investigation in
places with great industrial activity, residences, and highways. They verified the
presence of lead, cadmium, chromium, and nickel. Other studies have also
demonstrated the absorption capacity of metals in different parts of medicinal plants,
with heavy metals reported as lead, cadmium, chromium, nickel, copper, and zinc
(Zn) (Subramanian et al. 2012; Karahan et al. 2020).
Regarding medicinal plants, the most common observed consequences were a
reduction in biomass, a reduction in chlorophyll values, and an increase in MDA
content. For example, Acalypha indica L. lead contamination at 500 mg L
-1
reduced
root and shoot size by 50%, with a decline in chlorophyll a and b values and an
increase in MDA content (Venkatachalam et al.
2017). On Mentha crispa L., the
accumulation of lead in the roots caused a decrease in the size of the root system due
to the restriction of the cell division process (Sá et al. 2015). On the other hand,
Gautam et al. (2017) reported an increase in the EO content of Cymbopogon citratus
(D.C.) Stapf exposed to soil with different levels of heavy metals. Therefore, the
exposure of medicinal plants to heavy metals must be accompanied and monitored
for levels accepted by the plants that do not compromise the development of the
plants.
4.6 Ultraviolet Radiation in Medicinal Plants
Given the biochemical apparatus present in medicinal plants, the effect of ultraviolet
radiation is less harmful when compared with other abiotic stresses, with the result
being positive mainly for the production of phenolic compounds (Li et al. 2020b)
and some negative for photosynthetic damage since ultraviolet radiation induces
photo-oxidation with the formation of free radicals (Jaiswal et al.
2020). Recent
research in some species, damage to plants from UV-B and UV-C exposure was
verified, as these types of radiation promote the formation of free radicals. For
example, in Curcuma caesia Roxb. The appearan ce of singlet oxygen and peroxides
has been reported following exposure to UV-B light (Jaiswal et al.
2020
). In aquatic
Mentha, UV-B light reduced the photosynthetic rate with effects on chlorophyll and
increased MDA (Nazari and Zarinkamar 2020). Exposure to UV-B light signifi-
cantly (21%) increased MDA content in Crocus sativus L. plants (Rikabad et al.
2019).
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50 T. B. dos Santos et al.
4.7 Genomics Approaches to Understand Abiotic Stress
Responses in Medicinal Plants
Plants are considered medicinal due to the production of secondary metabolites that
are beneficial for human health (Memarzadeh et al. 2020). In addition, secondary
metabolites produced from these plants have pharmaceutical value and play an
essential role in adapting plants to environmental variations (Bouzid et al.
2023).
Secondary metabolites are chemical compounds unrelated to normal plant growth
and development (Bonacina et al.
2022a). Therefore, they are synthesized in differ-
ent plant parts in response to adverse environmental conditions (Bonacina et al.
2022b). To minimize the biological loss caused by stresses, plants accumulate
various reactive oxygen-scavenging enzymes (Laloi et al. 2004), phytohormones,
and secondary metabolites (Spoel and Dong 2008). The precursors for synthesizing
secondary metabolites are carbohydrates, amino acids, lipids, and nucleotides. These
compounds’ biosynthesis, concentration, and transport are strongly influenced by
cultivation conditions, such as habitat, harvesting time, climate, and soil nutrition
status (Falk et al.
2007; Bachheti et al. 2022). The interaction of plants with various
climatic conditions drives the biosynthesis of secondary metabolites, which are
classified into three major groups based on their origin: terpenoids, phenolics, and
nitrogen containing compounds.
The contents of secondary metabolites are modified under stress conditions in
medicinal plants because the genes involved in secondary metabolic pathways are
affected by different stresses (Sharma 2018). The development in the field of
genomics enabled plant scientists to understand gene expression and its relationship
to response to abiotic stresses. In response to various challenging climatic
conditions, the plant initiates a physiological response at the transcriptional level,
which activates post-translational protein modifications that affect metabolite alter-
ation and accumulation, resulting in a specific physiological response to abiotic
stresses (Fig. 4.2) (Singh et al. 2020). Abiotic stress signaling in plants involves
receptor-coupled phosphorelay, phosphoinositol-induced Ca
2+
changes, and
mitogen-activated protein kinase cascades followed by transcriptional activation of
stress-responsive genes (Sharma 2018; Hirayama and Shinozaki 2010). Abiotic
stresses are respon sible for synthesizing and accumulating amino acids, proteins,
nucleic acids, and carbohydrates, which cause stimuli to the cells as signaling
cascades through plasmodesmata (Kaur and Gupta 2005; Kumar et al. 2022). The
stress-inducible genes encode proteins (chaperons) as well as the signal transduction
to express enzymes (phosphatases, protein kinases), transcription factors, and phos-
pholipid metabolism enzymes for cell protection (Yamaguchi-Shinozaki and
Shinozaki
2005). The expression of the genes is led by DNA methylation and
RNA polymerase II (Maunakea et al. 2010; Shen et al. 2017). Furthermore,
according to several plant genome sequencing reports, many transcription factor
coding genes are also expressed as stress-responsive genes (Singh et al. 2002; Zhang
et al. 2022).
Gene expression research is essential to understanding medicinal plants’
responses to adverse environmental conditions (Li et al.
2020a). This process reveals
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the production of various metabolites that aid plant survival under adverse
conditions. Among the main metabolites, secondary metabolites are produced by
the plant as various abiotic stresses progress. Plant metabolism can be disrupted due
to a lack of enzymes or substrates; it can also be disrupted due to a higher
requirement for a specific compound or a combination of these factors. There have
4 Resilience Mechanism of Medicinal Plants Under Harsh Environment 51
Fig. 4.2 Model abiotic stress-signaling pathways in medicinal plants
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been some studies on the effect of abiotic stress on the gene expression of secondary
metabolites in medicinal plants. For example, in Artemisia annua, the sterol C-4
methyl oxidas e gene (SMO1) is responsible for increased sterol production and
tolerance to dehydration/drought stress (Singh et al.
2002). In another study, drought
stress may promote baicalin accumulation by increasing the expression and activities
of key enzymes, such as phenylalanine ammonia-lyase (PAL), cinnamate
4-hydroxylase (C4H), 4-coumarate CoA ligase (4CL), and chalcone synthase
(CHS) are involved in baicalin biosynthesis in Scutellaria baicalensis Georgi
(Cheng et al.
2018). In Glycyrrhiza uralensis, drought stress increased the levels
of jasmonic acid, glycyrrhizic acid, and flavonoids, as well as the expression of
genes that regulate the synthesis and transduction pathways (Yao et al.
2022).
52 T. B. dos Santos et al.
Plants under s
alt stress may also alter secondary met abolite content and gene
expression (dos Santos et al.
2022a). Chen et al. (2023 ) demonstrated that salinity
increased the expression of genes involved in flavonoid glucoside biosynthesis and
salt tolerance, including transcription factors, transporters, glucosyltransferase, heat
shock protein, and plant hormone signal transduction-related protein in Apocynum
venetum L. Furthermore, this author showed that the candidate gene AvUGT
(Tr AVENL 25169), which encodes UDP-glucosyltransferase, is likely to be impor-
tant in the biosynthesis of flavonoid glucosides in response to salt. The accumulation
of flavonoid glycosides in A. venetum L was consistent with the transcript profiles of
UGT genes. Plants have shown a coordinated change at the transcriptional level in
response to temperature stresses. When chilling and heat shock were applied to
Artemisia annua, the transcription levels of the amorpha-4,11-diene synthase (ADS)
and cytochrome P450 monooxygenase (CYP71AV1) genes increased when com-
pared with control plants (Yin et al. 2008). These are mostly the genes that code for
osmoprotectants, detoxifying enzymes, transporters, and regulatory proteins.
Salinity at 25 °C increased the relative level of phenolic compounds, proline, and
antioxidant activity in Mentha piperita L., according to Gholamnia et al. (
2022).
Furthermore, gene expression analysis revealed a significant increase in
hydroxyphenylpyruvate reductase (HPPR) and C4H gene expression and a signifi-
cant decrease in rosmarinic acid synthase (RAS) expression in plants exposed to
salinity and thermal stresses at the same time. Higher levels of C4H and HPPR
expression show the roles of these genes in defense processes and the benefits of
phenolic substances on oxidative stress inhibition (Gholamnia et al.
2022). These
studies reveal that abiotic stress-responsive metabolites are produced/consumed by
various pathways/cycles; new technological approaches, such as genomics,
transcriptomics, and proteomics, may aid in identifying and understanding the
abiotic-responsive pathways/cycles involved in the response and the establishment
of enhanced tolerance to different abiotic stresses.
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4 Resilience Mechanism of Medicinal Plants Under Harsh Environment 53
4.8 Omics as Biotechnological Tools in Medicinal Plants
Medicinal plants are recognized as an important source of substances (natural
products) that can be used for therapeutic purposes (Sofowora et al. 2013). About
80% of people worldwide use medicinal plants to meet their primary healthcare
needs (da Silva and Padilha
2022; Xia et al. 2022). Although natur al products from
medicinal plants can also be used in the industry as condiments, food additives, and
EOs (Alami et al.
2022). Despite their great importance in human health, the use of
medicinal plants has been severely affected by human activities and climate change
(Xia et al.
2022). In addition, medicinal plants have yet to be forgotten in domesti-
cation compared with crop species, such as wheat, soybean, maize, rice, and potato
(Siahsar et al.
2011; Niazian 2019). To overcome these issues, the use of
biotechnology-based methods contributes to better deciphering the metabolism and
genetic traits of medicinal plants. With the advent of the post-genomic era, omics
approaches (genomics transcriptomics, pmecinroteomics, and metabolomics) have
emerged as valuable tools to characterize and quantify the pools of biological
molecules within organisms (organs, tissues, and cells) covering a wide range of
molecular information, including structure, biosynthesis, function, regulation diver-
sity and dynamics. Next-generation sequencing (NGS) revolution ized genomic and
transcriptomic research, allowing high-throughput sequencing of either DNA or
RNA (Phillips
2018). At the same time, advances in chromatography and mass
spectromerry-based approaches contributed significantly to the large-scale profiling
of proteins and metabolites in plants (Rodrigues et al. 2021). In this context, single
and multi-omics techniques have brought unprecedented opportunities for
unraveling signaling interaction networks and vital molecular targets of medicinal
plants (Dai et al.
2022). In this topic, we highlight the use of omics platforms to study
the molecular responses of medicinal plants to abiotic stre sses.
4.9 Genomics in Medicinal Plants
NGS techniques allow researchers to obtain the whole genomic and transcriptomic
information of model and non-model plants. A high-quality genome sequence could
lead to extensive and in-depth molecular genetics research and play a significant role
in identifying genes related to the biosynthesis of targeted molecules (Alami et al.
2022). With the development of sequencing technology and parallel reduction in the
sequencing costs, genomics and transcriptomics analyses of medicinal plants have
been published using or combining third-generation (long-read sequencing using
platforms, such as Pacific Biosciences and Oxford Nanopore Technology (ONT))
with second-generation sequencing technology (short reads sequencing using
Illumina platform) (reviewed by (Alami et al.
2022; Cheng et al.
2021)). In addition,
high-throughput chromosome conformation capture (Hi -C) sequencing has also
been used in medicinal plants, in combination with short and long reads sequencing
((Ma et al. 2021; Zhou et al. 2022; Yu et al. 2022), and reviewed by (Alami et al.
2022)).
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54 T. B. dos Santos et al.
The acquisition of whole-genome sequencing contributed to fundamental
research on medicinal plants molecular breeding and accelerated the cultivation
process of varieties (Alami et al. 2022). In addition, whole-genome sequencing
facilitates plants’ structural, comparative, phylogenetics, and evolutionary genomics
analysis. Examples of recently published genomics studies in medicinal plants were
reviewed by Alami et al. (
2022) and include genome sequencing and de novo
assembly (Ma et al.
2021; Xia et al. 2020; Song et al. 2020; Liu et al. 2021; Ren
et al. 2021; Miao et al. 2022), chromosome scale (Cheng et al. 2021; Xie et al. 2020;
Rai et al. 2021; Chang et al. 2022), and evolutionary analysis (Ren et al. 2021; Rai
et al.
2021; Kang et al. 2021). The genome sequence of Mitragyna speciosa
(kratom), Gelsemium sempervirens , Calotropis gigantea, Camptotheca acuminata,
and C. roseus are available at the webpage Medicinal Plant Genomics Resource
(
http://mpgr.uga.edu/).
4.10 Transcriptomics in Medicinal Plants
Transcriptome sequencing (RNA-seq) is a high-throughput, high-resolution, and
high-sensitivity technique (Guo et al. 2021), and it is not limited to a reference
genome. RNA-seq technologies have various applications, including the following:
(1) differential expression analysis; (2) transcriptome de novo assembly; (3) detec-
tion of new transcripts or correction of existing genes; (4) construction of expression
atlas; (5) construction of gene co-expression networks (GCNs) and prediction of
gene regulatory networks (GRN); and (6) structural alterations (Tu et al.
2022; Yang
et al. 2023). As mentioned previously, RNA-seq can be performed using short-read
and long-read Technologies [reviewed by (Tu et al. 2022; Amarasinghe et al. 2020;
Oikonomopoulos et al. 2020; Tyagi et al. 2022). RNA-seq studies have been
conducted in medicinal plants to investigate transcriptional modulation in response
to abiotic stresses. Qian et al. (2021
) investigated the morpho-physiological
responses and transcriptomic signatures of Polygonatum kingianum in response to
mild, moderate, and severe drought and rewatering. In total, 1352 and 350 differen-
tially expressed genes (DEGs) were found in drought and rewatering plants, respec-
tively. Drought stress affects DEGs related to phenylpropanoid, flavonoid,
stilbenoid, gingerol, and carotenoid biosynthesis pathways and starch and sucrose
metabolism. In parallel, the authors found that plant-pathogen interaction and
galactose metabolism pathways were differentially regulated between severe
drought and rewatering (Qian et al.
2021). In both given examples, RNA-seq
analysis was carried out through the Illumina sequencing platform, Kuang et al.
(
2022) described for the first time the use of the ONT to investigate Salvia
miltiorrhiza transcriptional and post-transcriptional regulation in response to treat-
ment with abscisic acid (ABA), that plays a central role in mediating plant responses
to environmen tal stresses. Authors found that ABA induced the expression pattern
variation of many genes involved in multiple biological processes, which is consis-
tent with the central role of ABA in response to abiotic stress. In parallel, authors
reported that ABA could evoke post-transcriptional splicing converting intron-
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containing transcripts into mature mRNA for protein synthesis (Kuang et al. 2022 ).
With the combination of transcriptome and metabolome profiling analysis (Li et al.
2020c) moderate drought-improved tea (C. sinensis L.) flavor by balancing levels of
specialized metabolites. Authors reported that the differential accumulation of
flavonoids and lipids played a crucial role in tea flavor and that genes, such as
type III polyketide synthase B and flavonol synthase/flavanone 3-hydroxylase,
played essential roles in flavonoid accumulation (Li et al.
2020c)
.
4 Resilience Mechanism of Medicinal Plants Under Harsh Environment 55
4.11 Proteomics in Medicinal Plants
Identifying plant-derived natural products is underway, although this is a difficult
task due to the high number of secondary metabolite classes and the complex
biosynthesis of these compounds, which are the sum of plant genetics and responses
to environmental stresses (Hashiguchi et al. 2017). In these terms, the proteomic
approach could be a powerful tool to elucidate key proteins to control metabolic
pathways that synthesize bioactive compounds in medicinal plants. Proteomics aims
to characterize from a structural and biol ogical point of view as many proteins as
possible in a biological unit (cell, tissue, and organ) (Jorrin Novo 2021). The
proteome analysis identifies the total proteome, its qualitative presence and quanti-
tative abundance, variation within a population, localization, and post-
transcriptional modifications (Balotf et al. 2022). In medicinal plants, proteomics
approaches have been applied to identify and quantify the proteome regulation in
response to environmental stresses (Kim et al. 2019; Gu et al. 2020; Park et al. 2022;
Taghvaei et al.
2022; Galic et al. 2022). Kim et al. (2019) performed a shotgun
proteomics approach to investigate the effect of heat stress on ginseng (Panax
ginseng) leaves. The proteome analysis led to the identification of 847 proteins
differentially modulated in response to heat stress. Proteins with increased abun-
dance were mainly associated with antioxidant and translation-regulating activities,
whereas those exhibiting decreased abundance were the proteins related to the
receptor and structural-binding activities (Kim et al.
2019). Cold tolerance of two
genotypes of Camellia japonica was investigated by combining transcriptome,
proteome, and hormonal analysis (Fan et al.
2022
). Authors found 60% of the
genes responding to cold exhibiting similar dynamics in the two genotypes (temper-
ate and subtropical), 1896 transcripts, and 455 proteins accumulated differentially in
response to cold between both genotypes. Ribosomal protein and genes related to
photosynthesis were upregulated in Tg C. japonica. The results revealed a putative
model of differential cold tolerance in C. japonica genotypes, in which genes acting
in photosynthesis, secondary metabolism, and hormone-related pathways (mainly
the ration ABA/gibberellic acid) modify cold resistance in C. japonica (Fan et al.
2022).
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56 T. B. dos Santos et al.
4.12 Metabolomics in Medicinal Plants
Plants exposed to environmental and abiotic stresses are subjected to various
morphological and physiological changes leading to alterations in plant chemical
composition. To overcome such stressors, plants may mount a defense response by
producing diverse secondary metabolites, avoiding cell and tissue damage (Yeshi
et al.
2022). As recently revie wed by Yeshi et al. (2022), the most popular plant
secondary metabolites-derived drugs are morphine (from Papaver somniferum),
digitoxin (from Digitalis purpurea), taxol (from Taxus baccata), artemisinin (from
Artemisia annua), quinine (from Cinchona officinalis), vinblastine and vincristine
(from C. roseus), and aspirin (first isolated as salicylic acid from Filipendula
ulmaria). Based on biosynthetic pathways, the three major plant seconda ry
metabolites groups are the following: (1) terpenes (e.g., volatiles, sterols,
carotenoids, saponins, glycosides); (2) phenolics (e.g., flavonoids, lignin, coumarins,
stilbenes, and tannins), and (3) nitrogen-containing compounds (e.g., alkaloids,
glucosinolates, and cyanogenic glycosides) (Fang et al.
2011; Jamwal et al. 2018).
Metabolomics is a powerful tool to investigate plants’ metabolic adjustments (e.g.,
secondary metabolite biosynthesis) in response to stresses, and it has been used in
medicinal plants (reviewed by (Yeshi et al.
2022)). Recently, Shen et al. (2022)
evaluated the metabolomic and lipidomic dynamic changes in leaves of tea
(C. sinensis L.) plants under drought stress and rewatering. The authors found that
severe drought stress evoked the accumulation of sucrose, cellotriose, turanose, and
different phosphatidic acid species. While organic acids, phosphatidylglycerol,
sulfoquinovosyl-diacylglycerol, phosphatidylcholine, lyso-phosphatidylcholine,
and phosphatidylinositol, decreased significantly in tea leaves under drought stresses
(Shen et al. 2022). In another study with C. sinensis L., metabolomics was performed
to evaluate the metabolic responses of tea plants to cold stress and explore the role of
5-aminolevulinic acid (ALA) in improving cold-resistance capability in tea plants
(Yan et al.
2022). Authors reported that cold stress altered various metabolites in tea
tissues, especially flavonoids and galactose. ALA application increased the contents
of flavonoids associated with cold stress (e.g., catechin, 3,4-dihydroxyphenylacetic
acid, and procyanidin B2), and galactose was found to have a role in the mechanisms
of ALA-promoted cold resistance in tea plants (Yan et al.
2022).
Although, in this topic, we have shown the use of omics approaches, other
important biotechnological tools, such as genome-wide association studies, meta-
bolic quantitative trait loci, transgenesis (gene transfer or gene silencing), genome
editing methods (transcription activator-like effector nucleases), Zn-finger
nucleases, and clustered regularly interspaced short palindromic repeats (Cas9) are
being used to improve the scientific community’s knowledge of metabolic regulation
in medicinal plants (reviewed by (Alami et al.
2022; Niazian
2019; Ricroch et al.
2022)).
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4 Resilience Mechanism of Medicinal Plants Under Harsh Environment 57
4.13 Use of New Biotechnological Tools in the Promotion
of Medicinal and Aromatic Plants’ Tolerance to Stresses:
The Example of Selenium and Silicon Fertilization
Novel and sustainable agronomic practices have recently been adopted to improve
medicinal and aromatic plants’ resilience to abiotic stresses. Among these practices
can be cited the use of benefic mineral elements like selenium (Se) and silicon (Si).
These beneficial elements play important roles in growth, physiology, and metabo-
lism and promote plant stress mitigation (Kumar et al.
2016; Li et al. 2021). Their
additional roles in bioactive compound biosynthesis in medicinal and aromatic
plants are a relatively novel line of research with great application potential.
Se exerts effects on sulfur (S) and nitrogen metabolisms, influencing the synthesis
of proteins and amino acids, such as methionine, tyrosine, phenylalanine, and
tryptophan, which act as glucosinolates precursors, phenolic biosynthesis substrates,
and so on. Se application may explore the existing variation in plant species in the
accumulation of Se, the expression of sulfate transporters, the form(s) of
accumulated Se, and the content of various S/Se metabolic enzymes (Malagoli
et al.
2015). Furthermore, Se shows pronounced toxicity at elevated concentrations,
contradicting the concentrations of S, N, P, and many amino acids and suppressing
the absorption of Cd, Cu, Zn, and Mn (Schiavon and Pilon-Smits
2017a). The
margin between the two roles relies on its speci ation, appropriate dose, and various
variables that are induced by the environment (Germ et al.
2007).
Se appli cation at low concentrations in medicinal species can promote plant
growth, increase yield, and counteract oxidative stress. Additionally, Se can improve
the levels of phytochemicals in these species (Islam et al.
2020). Therefore, Se
biofortification is considered a sustainable and cost-effective strategy to enhance
nutritional and functional quality in food crops (Hu et al.
2018; Ramalho et al. 2020).
For example, in Se-biofortified tomato fruits, increased contents of antioxidative
flavonoids like chalcone, naringenin, and kaempferol were recorded following
selenite administration via foliar spray (Schiavon and Pilon-Smits
2017b).
Diverse roles played by Se in alleviating different types of abiotic stress in plants
are typified via upregulation and downregulation of various genes, proteins,
enzymes, and physiological parameters. Se-mediated abiotic stress eliminates reac-
tive oxygen species (ROS), modulating the antioxidant response (Ghorai et al.
2022). This element increases enzymes activity, such as superoxide dismutase
(SOD-EC 1.15.1.1), catalase (CAT-EC 1.11.1.6), ascorbate peroxidase (APX-EC
1.11.1.11), glutathione reductase (GR-EC 1.6.4.2), peroxidase (POD-EC 1.11.1.7),
and glutathione peroxidase (GSH-Px-EC 1.11.1.9) and positively impacts the hor-
monal balance of plant cells (Tavanti et al.
2021
). The levels of non-enzymatic
antioxidants are also improved by Se exogenous application. For example, the level
of α-tocopherol was increased in Se-treated green tea leaves (Xu et al. 2003).
α-Tocopherol (vitamin E) deactivates photosynthesis-derived ROS (primarily 1O2
and OH) and mitigates lipid peroxidation in the thylakoid membranes (Munn-
é-Bosch 2005).
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