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(continued)
47. Salt stress Radish Raphanus
sativus
Exogenous
melatonin
Flower Increased, plant height chlorophyll content,
miRNAs, endogenous hormones levels
Yildirim et al. (2008),
Sun et al. (2015)
48. Salt stress Maize, Zea mays Exogenous
melatonin
Fruit Increased antioxidant enzymes, and lipid
peroxidation
de Azevedo Neto et al.
(2006), Jasim et al.
(2016)
49. Salt stress Arabian coffee, Coffea
arabica
Exogenous
melatonin
Seeds Enhanced carboxylation process Campos et al. (2019)
50. Salt stress Pistachio, Pistacia vera Exogenous
melatonin
– Increase endogenous polyamine Kamiab (2020)
51. Salt stress Naked oat, Avena nuda Exogenous
melatonin
Seed Enhanced seedling growth, chlorophyll
content
Gao et al. (2019)
52. Salt stress Alfalfa, Medicago
sativa
Exogenous
melatonin
– Increases ROS scavenging and antioxidant
enzyme activity
Cen et al. (2020)
53. Heavy metal
lanthanum
Tomato, Solanum
lycopersicum
Endogenous
melatonin
Fruit Induced ROS production Maggio et al. (2007)
54. Fe
deficiency,
cadmium
Thale cress, Arabidopsis
thaliana
Exogenous
melatonin
– Induced polyamine, NO production Zhou et al. (2016)
55. Fluoride
toxicity
Rice, Oryza sativa Exogenous
melatonin
Seed Increased polyamine biosynthesis and
regulated abscisic acid
Singh et al. (2022)
56. Cd stress Cucumber, Cucumis
sativus
Exogenous
melatonin
Cortex Upregulation of ethylene response factors,
increased catalase, superoxide dismutase
activity, ascorbate peroxidase
Shah et al. (2020)
57. Heavy metal Kale or cabbage,
Brassica oleracea
Exogenous
melatonin
Leaf Lowers membrane peroxidation and
increases seed germination
Posmyk et al. (
2008)
58. Heavy metal Alfalfa Medicago sativa Exogenous
melatonin
– Redox homeostasis maintenance Gu et al. (2017)
59. Heavy metal Wheat, Triticum
aestivum
Exogenous
melatonin
Seed Enhances chlorophyll content,
photosynthetic carbon assimilation,
Rubisco, and ATPases activity
Zuo et al. (2017)
16 Role of Phytomelatonin in Plant Tolerance Under Environmental Stress 285
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Table 16.1 (continued)
Sr.
no.
Stress
condition Plant Mechanism
Melatonin
in plant
organ Effect Reference
60. Heavy metal Tobacco, Nicotiana Exogenous
melatonin
Stem tuber Lowers ROS burst and enhances cell
culture growth
Kobylińska and
Posmyk (2016 )
61. Heavy metal Watermelon, Citrullus
lanatus
Exogenous
melatonin
– Increases chlorophyll content, plant
growth, and enzymatic activity
Nawaz et al. (2018)
62. Heavy metal Tomato Solanum
lycopersicum
Endogenous
melatonin
– Enhances photosynthetic rate, plant
biomass, antioxidant efficacy, glutathione,
phytochelatins levels
Hasan et al. (2015)
63. Chromium,
aluminum
stress
Maize or corn, Zea mays Exogenous
melatonin
Corn Increase root diameter, tips, surface area,
volume, and water retention
Malik et al. (2021)
64. Copper ions Melon, Cucumis melo Exogenous
melatonin
– Enhances antioxidant activity and root
vigor, lowers proline and malondialdehyde
content
Hu et al. (2020)
65. Cadmium
toxicity
Chinese
cabbage,
Brassica rapa subsp.
pekinensis
Exogenous
melatonin
Corm Reduces amassing of nitric oxide, increases
photosynthetic rate and biomass
Wang et al. (2021)
66. Lead Safflower, Carthamus
tinctorius
Exogenous
melatonin
– Decrease translocation roots and Pb uptake Chamanara et al.
(
2019)
67. Arsenic The tea plant, Camellia
sinensis
Exogenous
melatonin
leaves Enhanced biosynthesis of anthocyanin Li et al. (2021)
68. Cadmium Tamarillo,
Cyphomandra
betacea
Exogenous
melatonin
– Increased growth Lin et al. (2018)
286 S. Kumar et al.
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their ability to grow and develop. Phytomelatonin can help alleviate this stress by
scavenging free radicals. Study on tomato plant found that exposure to high levels of
light led to an increase in phytomelatonin levels in the plants. This increase in
phytomelatonin was associated with a reduction in oxidative stress and an improve-
ment in the growth and development of plants. Overall, the role of phytomelatonin in
response to light stress is to help plants cope with the s
tress and protect them from
oxidative damage.
16 Role of Phytomelatonin in Plant Tolerance Under Environmental Stress 287
16.4.2 Cold and Heat Stress
Phytomelatonin helps plants cope with temperature stress, both heat and cold, and
protects them from oxidative damage. The specific temperature range that triggers
phytomelatonin production may vary depending on the plant species and environ-
mental conditions. Both cold and heat stresses made alterations in the redox homeo-
stasis. When plant experienced temperature stress, melatonin protects against
oxidative damage due to the ROS production (Ahmad et al. 2019).
When plants grow in the presence of low temperatures or cold, their metabolism
would slow down, and ROS are accumulated inside the cell that can cause cellular
damage. The principal process that is impacted by cold stress is photosynthesis (Goh
et al. 2012). Phytomelatonin can help prevent this damage by activating antioxidant
systems that scavenge ROS and protect the plant from damage. The specific temper-
ature range that triggers phytomelatonin production in response to cold stress also
varies depending on the plant species, but it is generally in the range of 0–15 °C
(Kong et al. 2020).
In response to high-temperature stress or heat, such as heat waves or exposure to
direct sunlight, phytomelatonin levels can increase in plants. This increase in
phytomelatonin is associated with a reduction in ROS production and an improve-
ment in plant growth and development (Zhang et al. 2013). The specific temperature
range that triggers phytomelatonin production may vary depending on the plant
species and environmental conditions, but it is generally in the range of 30–40 °C.
Melatonin reduces heat-induced stress by preserving redox status and controlling the
synthesis of nitric oxide and polyamines, according to research on Solanum
lycopersicum (Jahan et al. 2019). Due to its powerful antioxidant mechanism,
melatonin treatment enhances the germination % by 60% in heat-stressed seeds in
Arabidopsis thaliana (Hernández et al. 2015).
16.4.3 Drought/Water Stress Response
According to Ahmad et al. (Ahmad et al. 2017), drought stress is the main abiotic
stress that restricts the growth rate and production yield of crops. Due to its negative
effects on several biochemical and physiological processes in plant cells, drought
stress is a major concern that ceases the development and production of crops
(DaCosta and Huang 2007). Application of melatonin reduces the effects of drought
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on the seed germination and root elongation (Dai et al. 2020). The capacity of plants
to modify their growth and metabolism in response to stress fluctuates. By preserv-
ing metabolic homeostasis, resistant plants can develop a much less stressed state
that allows them to withstand specific abiotic stress. Sensitive plants exhibit reduced
growth and yield; in extreme circumstances, they succumb to an unable to maintain
metabolic balance (Jogaiah et al.
2013). Drought is a major factor that restricts
seedling establishment and germination in rain-fed environments (Khakwani et al.
2011). Plants under drought stress exhibit decreased transpiration rates and poor
active transport, which adversely affects the movement of nutrients from the roots to
the shoots and significantly lowers total biomass (Griffiths and Parry
2002). Addi-
tionally, pearl millet (Pennisetum glaucum L.) may become completely sterile after
being exposed to drought, most likely as a result of disrupted nutrient transport
(Yadav et al. 2004). When plants are subjected to drought conditions, they experi-
ence water stress, and this stress can disrupt the normal functioning of the plant cell.
Phytomelatonin helps regulate the plant’s response to water stress by controlling the
expression of stress-responsive genes, improving water u ptake and use efficiency,
and promoting plant survival (Fahad et al.
2017). Phytomelatonin can help plants to
adapt or overcome drought conditions, thus increasing their tolerance to water stress.
Melatonin has also been shown to regulate certain gene expression responsible for
drought tolerance and to reduce water loss by regulating stomatal opening and
closing (Turner et al.
2004).
288 S. Kumar et al.
16.4.4 Salt Stress Response
One of the major challenges across the world that can lower the plant growth and
development is salt stress. It induces physiological damage and water deficiency to
the plants (Shannon 1997). Phytomelatonin is known for its response to abiotic stress
in plants, including salt stress. High salt levels in soil, can lead to the salt stress that
can result in plant growth damage to the plant’s growth, development, and overall
health. Phytome latonin helps regulate the plant’s response to salt stress by
controlling the expression of stress-responsive genes, improving salt tolerance, and
modulating plant growth and development (Roy et al.
2014). Additionally,
phytomelatonin may help reduce the negative effects of salt stress on plant photo-
synthesis and water uptake, allowing the plant to maintain grow th and survi val under
salt stress conditions. Thus, it plays a major role in stress response and can help
improve salt tolerance in plants (Rajendran et al. 2009). The exact mechanism by
which phytomelatonin mediates the response of plants to salt stress is not fully
understood. However, studies have shown that phytomelatonin plays a role in the
regulation of stress-responsive genes and enhances the growth and development of
plant tolerance. Roy et al.
2014; Ismail et al. 2007; Maischak et al. 2010, investigated
some of the mechanisms of stress regulation which are as follows:
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16 Role of Phytomelatonin in Plant Tolerance Under Environmental Stress 289
Gene Regulation Phytomelatonin has the capacity to modify the stress-responsive
gene expression that plays a role in improving salt tolerance, such as genes involved
in ion transport, osmoprotectant, and antioxidant defense.
Antioxidant Defense Phytomelatonin can activate the plant’s antioxidant defense
system, which helps to scavenge ROS and combat the damaging effects produced
under salt stress.
Modulation of Plant Growth Phytomelatonin can modulate plant growth by
regulating hormone signaling pathways, such as the abscisic acid pathway, involved
in plant stress response.
Osmoprotection Phytomelatonin can improve salt tolerance by reducing the
adverse effects produced by high salt concentrations on plant water uptake and
maintaining cellular turgor, thus preventing wilting.
These mechanisms suggest that phytomelatonin plays a multifaceted role in the
response of plants to salt stress, protecting against salt-induced damage and improv-
ing salt tolerance (Isayenkov and Maathuis
2019). There are several examples of
salt-tolerant plants that have been found to have elevated levels of phytomelatonin:
Arabidopsis thaliana This is a model plant species widely used in the research
field of plant biology. Studies have shown that Arabidopsis plants with higher levels
of phytomelatonin are more tolerant to salt stress (Chen et al. 2017).
Rice (Oryza sativa). Rice is a widely grown staple crop in the areas with high soil
salinity. Rice plants that have been genetically modi fied to produce higher levels of
phytomelatonin have been shown to have improved salt tolerance (Xie et al.
2021).
Wheat (Trit icum aestivum). Wheat is a major food crop and is widely grown in
areas with saline soils. Studies have shown that wheat plants with higher levels of
phytomelatonin are more resistant and have improved growth and yields under salt
stress conditions (Ke et al. 2018).
Brassica napus Brassica napus is a species of oilseed rape that is widely grown for
its oil. Studies have shown that Brassica napus plants with higher levels of
phytomelatonin have improved salt tolerance with better growth and yields under
salt stress conditions (Zhao et al. 2019).
These examples demonstrate the efficacy of phytomelatonin in improvising salt
tolerance in crops and suggest that increased phytomelatonin levels can help plants
better adapt to and overcome salt stress conditions.
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290 S. Kumar et al.
16.4.5 Heavy Metal Stress Response
Heavy metal stress in plants refers to the harmful effects of excessive concentrations
of heavy metals as cadmium, lead, and copper in the soil or water on plant growth
(Ghori et al.
2019). Heavy metal stress can proceed to the oxidative stress, disrupt
ion balance, and cause damage to plant growth and development. Phytomelatonin
may help alleviate the negative effects of heavy metal stress by regulating the stress-
responsive gene expressions and modulating plant growth and development.
Phytomelatonin may also play a key role in the antioxidant defense mechanism,
helping to counteract oxidative stress caused by heavy metals (Zuo et al. 2017). In
addition, phytomelatonin also plays a role in the uptake and transport of heavy
metals, reducing the number of heav y metals that enter the plant and thus reducing
their toxicity. However, further study is required to understand the complete mecha-
nism of phytomelatonin-mediated responses in plants to heavy metal stress and to
determine its potential as a tool for improving heavy metal tolerance in crops. The
mechanism to resolve the problem of heavy metal stress in plants involves the
following steps (Ali et al. 2022):
1. Uptake of heavy metals. Plants absorb heavy metals through their roots or leaves,
and the met al ions accumulat e in different parts of the plants.
2. Disruption of cell ular processes. Heavy metals can disrupt various cellular pro-
cesses, including photosynthesis, respiration, and DNA replication, leading to
reduced growth and yield.
3. Oxidative stress. Heavy metals produce oxidative stress by generating ROS in
plants that can badly damage proteins, cell membranes, and DNA.
4. Chelation and detoxification. To mitigate the harmful effects of heavy metals,
plants can chelate the metal ions with organic compounds or sequester them in
vacuoles or detoxify them through enzymatic pathways.
Examples of heavy metal stress in plants include:
1. Cadmium (Cd) toxicity in rice: Cd, a toxic heavy metal, can accumulate in rice
grains, posing a health risk to humans.
2. Copper toxicity in tomatoes: High leaves of copper in the soil can reduce tomato
growth and fruit yield by affecting nutrient uptake and photosynthesis.
3. Lead pollution in urban plants: Lead, a common pollutant in urban areas, can
accumulate in plant tissues and affect their physiological functions, such as water
uptake and transpiration.
According to Jadhav et al. (Jadhav et al. 2021), understanding heavy metal stress
responses in plants can help to develop strategies to mitigate their harmful effects
and improve plant resilience in contaminated environments. The study of heavy
metal stress and phytomelatonin mechanism has several applications, including:
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16 Role of Phytomelatonin in Plant Tolerance Under Environmental Stress 291
1. Environmental monitoring. Understanding the impact of heavy metal stress on
plants can help identify contaminated sites and monitor the effectiveness of
remediation efforts.
2. Crop improvements. Heavy metals tolerant crop development can increase crop
yield and food security in contaminated areas.
3. Phytoextraction. Certain plants can accumulate heavy metals in their tissues,
making them suitable for phytoremediation, a process that involves using plants
to extract heavy metals from contaminated soil or water.
4. Pharmaceutical development. Phytomelatonin is a plant hormone that regulates
various physiological processes and has anti-inflammatory and antioxidant
properties. Studying its mechanism of action can lead to the development of
novel therapeutics for human diseases.
So, to understand the impact of heavy metal stress in plants and phytomelatonin
mechanism can have important implications for environmental, agricultural, and
biomedical research.
16.5 The Role of Phytomelatonin in Response to Biotic Stress
Phytomelatonin, which is a plant hormone, plays a major role in response to biotic
stress that is caused by pathogens, pests, herbivores, etc. According to Tiwari et al.
(Tiwari et al.
2021), the following are some of how phytomelatonin can modulate the
plants’ response to biotic stress:
1. Activation of defense mechanisms. Phytomelatonin can activate various defense
mechanisms in plants, such as the production of ROS, phytohormones, and
secondary metabolites, which can help plants to resist or tolerate biotic stress.
2. Induct ion of systemic acquired resistance. Phytomelatonin can induce systemic
acquired resistance (SAR) in plants, which is a broad-spectrum, long-lasting,
immunity against a range of pathogens. SAR can be triggered by the accumula-
tion of phytohormones, such as salicylic acid, and phytomelatonin has been
shown to modulate the level s of these hormones.
3. Regulation of gene expression. Phytomelatonin can regulate the gene expressions
that are involved in the plant’s response to biotic stress. For example,
phytomelatonin can upregulate the expression of genes that encodes
pathogenesis-related proteins, involved in plant defense.
Overall, the role of phytomelatonin at the time of biotic stress is an area of
research, and understanding the mechanisms involved could have important
implications for crop improvement and sustainable agriculture. Table
16.2 presents
example of the role of melatonin in biotic stress tolerance in plant.
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Mechanism Plant species Effect Reference
(continued)
292 S. Kumar et al.
Table 16.2 Role of melatonin in biotic stress tolerance in plants
Pathogen
Sr.
no.
Fungal pathogens
1. Exogenous Potato,
Solanum
tuberosum
Phytophthora
infestans
Increased
fungicide,
susceptibility,
disruption of
spores and
mycelia
Zhang
et al.
(
2017b)
2. Endogenous Banana,
Musa
acuminate
Fusarium
oxysporum
Heat shock
proteins
expression
regulation
Wei et al.
(
2018)
3. Endogenous Cucurbit,
Citrullus
lanatus
Phytophthora
capsici and
Podosphaera xanthii
Regulation of PTI
and ETI
Mandal
et al.
(2018)
4. Exogenous Strawberry,
Fragaria
ananassa
Rhizopus
stolonifera, Botrytis
cinerea
Maintain
intracellular
H
2
O
2
Aghdam
and Fard
(2017)
5. Endogenous Cucumber,
Cucumis
sativus
Pseudoperonospora
cubensis
Activation of
antioxidant genes
Sun et al.
(
2019)
6. Endogenous Apple,
Malus
prunifolia
Diplocarpon mali ROS scavenging
and activation of
defense genes
Yin et al.
(
2013)
7. Endogenous Cotton
Gossypium
spp.
Verticillium dahliae Increased
resistance,
promoted
gossypol and
lignin
accumulation
Li et al.
(
2019b)
Bacterial pathogens
8. Endogenous Thale cress,
Arabidopsis
thaliana
Pseudomonas
syringae
Upregulation of
defense gene PR1,
PR5, and plant
defensin
Lee et al.
(2014)
9. Endogenous Rice, Oryza
sativa
Xanthomonas
oryzae pv. oryzae
Downregulation
of bacterial
metabolic and
virulence genes
Chen
et al.
(2018b)
10. Exogenous Cassava,
Manihot
esculenta
Xanthomonas
axonopodis
Activation of
transcription
factors for disease
resistance
Wei et al.
(2018)
11. Endogenous Tobacco
plant,
Nicotiana
benthamiana
Pseudomonas
syringae
Upregulation of
plant defensin and
defense gene PR1,
PR5
Lee et al.
(2014)
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Mechanism Plant species Effect Reference
16 Role of Phytomelatonin in Plant Tolerance Under Environmental Stress 293
Table 16.2 (continued)
Sr.
no.
Pathogen
Fungal pathogens
Viral pathogens
12. Endogenous Eggplant,
Solanum
melongena
Alfalfa mosaic virus
(AMV)
Reduction of
H
2
O
2
Hydroxyl ions,
superoxide
anions, and
malondialdehyde
Sofy et al.
(
2021)
13. Endogenous Apple,
Malus
domestica
Apple stem grooving
virus
Virus eradication
from infected
shoots
Moustafa-
Farag
et al.
(
2019)
14. Endogenous Tomato,
Solanum
lycopersicum
Tobacco mosaic
virus
Elevated PR1 and
PR5 expressions
Zhao
et al.
(2019)
16.5.1 Bacteria-Mediated Response
Phytomelatonin, which is a form of the hormone melatonin produced by plants,
plays a key role bacteria-mediated stress response in plants. Specifically, it has been
found to enhance the plant’s defense response by regulating the gene expression
involved in the immune response and reducing the levels of ROS that can damage
plant cells. This can lead to improved resistance against bacterial infec tions and
improved survival and growth of plant under stress (Qian et al.
2015). There is
limited research on the role of phytomelatonin in bacteria-mediated response to
biotic stress. However, some studies suggest that phytomelatonin may play a role in
modulating the plant’s response to bacterial pathogens by regulating the expression
of genes involved in plant defense. For example, a study by Lee et al. (Lee et al.
2014) showed that exogenous application of phytomelatonin increased the resistance
of Arabidopsis plants to Pseudomonas syringae (a pathogen) by upregulating the
expression of gene encoding pathogenesis-related protein and increasing the pro-
duction of ROS. Another study by Chen et al. (Chen et al.
2018b) found that
phytomelatonin enhanced the antioxidant enzyme activity and scavenged the ROS
in rice plants infected with the bacterial pathogen Xanthomonas oryzae. This
suggests that phytomelatonin may help mitigate the oxidative damage caused by
bacterial infection. These studies suggest that phytomelatonin may be invol ved in
modulating the p lant’s defense response against bacterial pathogens (Tiwari et al.
2021).
When a plant is facing bacterial infection stress, it will mount a defense response
to protect itself. One way it does this is by producing reactive oxygen species (ROS),
which can be toxic to bacteria (Wei et al. 2018). However, if ROS levels get too high,
they can also damage the plant’s cells. To counteract this, the plant produces
antioxidants to scavenge excess ROS and protect its cells. In addition to this, the
plant may also produce phytomelatonin in response to bacterial infection.
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Phytomelatonin is synthesized from tryptophan via a series of enzymatic reactions,
and its production is upregulated in response to stress (Arnao and Hernández-Ruiz
2015). Once produced, phytomelatonin can help to reduce ROS levels and protect
the plant’s cells from damage. It can also regulate the expression of genes involving
in plant’s immune response, helping to enhance its defenses against bacteria.
294 S. Kumar et al.
Hence, the response
of plant immune system to bacterial infection involves a
complex interplay between ROS, antioxidants, and other signalin g molecules,
including phytomel atonin (Prakash et al.
2019). By understanding these processes,
researchers may be able to develop new strategies for protecting plants against
bacterial diseases and improving their overall health and productivity.
16.5.2 Fungi-Mediated Response
Fungi-mediated response in plants refers to how plants respond to fungal infections.
Fungi are a common cause of plant diseases, and plants have evolved various
mechanisms to defend themselves against fungal pathogens. One of the main ways
that plants respond to fungal infections is by producing specialized chemicals and
enzymes that can kill or inhibit the growth of the fungus (Mandal et al.
2018). For
example, some plants produce phytoalexins, which are toxic compounds that can kill
fungi on contact. Other plants produce chitinases, which break down the chitin in
fungal cell walls and inhibit their growth. In addition to producing chemical
defenses, plants may also engage in physical defenses, such as producing thicker
cell walls or forming structural barriers to prevent fungal penetration. They may also
activate their immune system, which can recognize and respond to fungal pathogens
(Zhang et al. 2017b).
In response to fungal infection stress, the plant may also produce phytomelatonin.
Its production is upregulated in response to various stressors, including fungal
infections. The synthesis of phytomelatonin in response to fungal infection stress
may occur through the shikimate pathway, which is a metabolic pathway that
produces several important plant compounds, including aromatic amino acids.
Tryptophan, which is an aromatic amino acid, can be converted to serotonin,
which is then converted to N-acetylserotonin, and finally to phytomelatonin. The
exact mechanisms of phytomelatonin to fungal infection are not fully understood,
but it is considered to play an important role in regulating the immune system of
plant and reducing the level of ROS that can damage plant cells. Overall, the plants’
response to fungal infection involves a complex interplay between various biochem-
ical and physiological processes, including the production of phytomelatonin (Chen
et al.
2018b). By understanding these processes, researchers may be able to develop
new strategies for protecting plants against fungal diseases and improving their
overall health and productivity. Moreover, the fungi-mediated response in plants is
a complex and coordinated process that involves multiple levels of defense. By
understanding these processes, researchers may be able to develop new strategies for
protecting plants against fungal diseases and improving their overall health and
productivity.
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