Brassinosteroids in Plant Tolerance to Abiotic Stress

Abstract

Brassinosteroids (BRs) are a group of plant steroid hormones with multiple roles in plant growth, development, and responses to stresses. In plants, BR deficiencies impair vital physiological processes and cause phenotypic abnormalities. A large number of studies show that BRs can positively influence plant responses to abiotic stresses such as heat, cold, drought, salinity, pesticides, and heavy metals. However, the underlying mechanisms of BR-induced stress tolerance are largely unclear. BR perception takes place in the cell surface by BR receptors, leading to a cascade of phosphorylation events to activate the central transcription factor BRASSINAZOLE-RESISTANT1 (BZR1) that controls the transcription of BR-responsive genes in the nucleus. BRs improve photosynthetic efficiency under stress conditions, which largely contributes to increased growth and biomass accumulation. Studies relating to exogenous BRs reveal a high dependency on concentrations with regards to BR effects on plants. Genetic studies show a positive correlation between the endogenous BR levels and abiotic stress tolerance, although this assumption contradicts with the performance of some BR mutants under stress conditions. Notably, plant responses to BRs greatly vary depending on the plant species, developmental stages, and environmental conditions. In addition, other hormones and signaling molecules that participate in fine-tuning the BRs effects also play an important role in plant adaptation to stress. Here, we review the involvement of BRs in plant responses to abiotic stresses. We also discuss available literature to show potential mechanisms of BR-induced abiotic stress tolerance. These studies signify the complexity of BR action in mediating stress responses in plants.

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Vol.:(0123456789)
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Journal of Plant Growth Regulation
https://doi.org/10.1007/s00344-020-10098-0
Brassinosteroids inPlant Tolerance toAbiotic Stress
GolamJalalAhammed1 · XinLi2· AirongLiu1· ShuangchenChen1
Received: 24 December 2019 / Accepted: 9 March 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Brassinosteroids (BRs) are a group of plant steroid hormones with multiple roles in plant growth, development, and responses
to stresses. In plants, BR deficiencies impair vital physiological processes and cause phenotypic abnormalities. A large num-
ber of studies show that BRs can positively influence plant responses to abiotic stresses such as heat, cold, drought, salinity,
pesticides, and heavy metals. However, the underlying mechanisms of BR-induced stress tolerance are largely unclear. BR
perception takes place in the cell surface by BR receptors, leading to a cascade of phosphorylation events to activate the
central transcription factor BRASSINAZOLE-RESISTANT1 (BZR1) that controls the transcription of BR-responsive genes
in the nucleus. BRs improve photosynthetic efficiency under stress conditions, which largely contributes to increased growth
and biomass accumulation. Studies relating to exogenous BRs reveal a high dependency on concentrations with regards
to BR effects on plants. Genetic studies show a positive correlation between the endogenous BR levels and abiotic stress
tolerance, although this assumption contradicts with the performance of some BR mutants under stress conditions. Notably,
plant responses to BRs greatly vary depending on the plant species, developmental stages, and environmental conditions.
In addition, other hormones and signaling molecules that participate in fine-tuning the BRs effects also play an important
role in plant adaptation to stress. Here, we review the involvement of BRs in plant responses to abiotic stresses. We also
discuss available literature to show potential mechanisms of BR-induced abiotic stress tolerance. These studies signify the
complexity of BR action in mediating stress responses in plants.
Keywords Brassinolide· Environmental stress· Photosynthesis· Reactive oxygen species· Stress responses
Introduction
Plants have to endure routine changes in environmental
parameters relating to diurnal and seasonal variations. In
addition, unusual weather events and environmental pollu-
tion often result in stresses on plants (Ahammed etal. 2014;
Fang etal. 2019). Since plants cannot relocate, their survival
largely depends on the timely perception of stress stimuli
and rapid responses to counter the stress effects (Nolan etal.
2019; Planas-Riverola etal. 2019). Plants utilize a num-
ber of signaling molecules, including hormones to medi-
ate plant responses to stressors (Wang etal. 2019a; Zhang
etal. 2019b; Zhou etal. 2019; Guo etal. 2019). Studies
have revealed that not a single hormone but a group of hor-
mones and signaling molecules collaborate to mediate plant
responses to a specific stress (Choudhary etal. 2012; Planas-
Riverola etal. 2019). Coordination of hormones and signal-
ing molecules fine-tune the responses of plants and eventu-
ally their survival under stressful conditions. Phytohormones
initiate a signaling cascade involving multiple molecular
players leading to an ideal generic pathway (Xiong etal.
2002). Basically, it starts from the perception of signals
on cell surface, followed by the generation of second mes-
sengers, such as reactive oxygen species (ROS) and nitric
oxide (NO), leading to protein phosphorylation cascades that
eventually activate transcription of stress-responsive genes
(Xia etal. 2009a, 2011, 2014; Yin etal. 2016). Nonetheless,
ideal spatiotemporal coordination among signal molecules
is important for plant adaptation to stress. In this review, we
* Golam Jalal Ahammed
ahammed@haust.edu.cn
* Xin Li
lixin@tricaas.com
1 College ofForestry, Henan University
ofScience andTechnology, Luoyang471023,
People’sRepublicofChina
2 Key Laboratory ofTea Quality andSafety Control,
Ministry ofAgriculture, Tea Research Institute, Chinese
Academy ofAgricultural Sciences, Hangzhou310008,
People’sRepublicofChina

Journal of Plant Growth Regulation
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discuss the roles of brassinosteroids (BRs), a unique group
of plant steroid hormones, in plant responses to various abi-
otic stresses such as heat, cold, drought, salinity, pesticides,
and heavy metals. We also discuss the mechanisms of BR-
mediated enhanced tolerance to abiotic stresses and the com-
plexity of BR action in mediating stress responses in plants.
BRs intheRegulation ofPlant Growth
andDevelopment
BRs play diverse roles in plant growth and development
(Fang etal. 2019; Peres etal. 2019). BRs biosynthetic and
signaling pathways have been extensively studied in model
plants, which have greatly improved our understanding of
the regulatory mechanisms of BRs, particularly in different
biological processes relating to plant growth and develop-
ment (Choe 2010; Zhao and Li 2012; Nolan etal. 2019;
Planas-Riverola etal. 2019). Initially, BRs-induced growth
promotion was thought to be a consequence of cell elonga-
tion. However, afterward, a role for BR in cell division was
also revealed. It is now well established that BRs regulate
multiple aspects of growth and development besides cell
elongation and cell division, such as xylem differentiation,
photomorphogenesis, plant reproduction, and responses to
abiotic and biotic stresses (Nolan etal. 2019). Although BRs
biosynthesis is thought to occur only in the endoplasmic
reticulum, BRs perception takes place at the cell surface
by the plasma membrane-localized receptors, BRASSI-
NOSTEROID INSENSITIVE1 (BRI1), and corresponding
homologs (Nolan etal. 2019; Northey etal. 2016). Upon BR
perception by BRI1 and co-receptors, BR signals are relayed
via a well-recognized signaling cascade to BRI1-EMS-SUP-
PRESSOR1 (BES1) and BRASSINAZOLE-RESISTANT1
(BZR1), downstream transcription factors, which eventu-
ally control transcription of BR-regulated genes (Nolan etal.
2019; Planas-Riverola etal. 2019; Tong and Chu 2018). In
plants, BR deficiency or BR perception inability results in
low seed germination, dwarfism, delay in flowering and
senescence, decreased male fertility, and de-etiolation in
the dark (Clouse 2015). On the other hand, overexpression
of BR biosynthetic genes increases endogenous BR levels
leading to increased crop yield and enhanced stress tolerance
(Divi and Krishna 2009; Xia etal. 2018). In rice, overex-
pression of a gene that encodes sterol C-22 hydroxylases
increases endogenous BR levels, leading to increased grain
size and yield up to 40% (Wu etal. 2008). A recent study
on soybean (Glycine max L. Merrill) showed that BR could
delay leaf senescence (Yin etal. 2019). Accumulating evi-
dence suggests that the capacity of BR in regulating impor-
tant agronomic traits has the potential to reshape the future
of agriculture (Divi and Krishna 2009; Tong and Chu 2018).
Role ofBRs inAbiotic Stresses
In addition to growth improvement, BRs play a crucial role
in environmental adaptions (Fig.1). With a few excep-
tions, BRs have been shown to improve plant adaptations
to biotic and abiotic stresses, such as drought, salinity,
heat, cold, heavy metals, pesticides, and organic pollut-
ant-induced stresses (Kagale etal. 2007; Rajewska etal.
2016; Xia etal. 2018). However, the mechanisms of BRs
action in enhancing plant tolerance to abiotic stresses still
remain largely unknown. In tomato (Solanum lycopersi-
cum L.), mutants of BRs biosynthesis (dwf) show sensi-
tivity to chilling stress, whereas overexpression of DWF
results in an increased cold tolerance (Fang etal. 2019;
Xia etal. 2018). Recently, BRs have been shown to be
involved in plant responses to nitrogen (N) starvation via
modulation of autophagy, a self-destructive mechanism
of cells, which is used by plants to mediate responses
to stresses (Wang etal. 2018). Exogenous BR enhances
the transcript levels of autophagy-related genes and the
formation of autophegosomes. While overexpression of
BZR1 enhances the formation of autophagosomes and tol-
erance to N starvation, silencing of BZR1 attenuates the
formation of autophagosomes and BR-induced tolerance
to N starvation. Nonetheless, exogenous BR application
aggravates plant sensitivity to iron deficiency, suggesting
the duality of BR action in plant tolerance to nutrient defi-
ciency (Wang etal. 2012a).
Among a large number of studies that reveal BR effects
on plants, most studies used pharmacological approaches
where exogenous BR was used to investigate thestress-
protective role of BRs (Ahammed etal. 2014). Different
modes of applications, such as pre-sowing seed treatment,
pre-planting dipping of cuttings, post-emergence root
treatment, foliar application, and so on have been used in
multiple plant species (Kagale etal. 2007; Sasse 2003; Yu
etal. 2004; Amraee etal. 2019; Yue etal. 2018; Yin etal.
2019; Sharma etal. 2016c, 2019). It is to be noted that BR
effects largely depend on a number of factors including
dose, plant species, growth stage, growth conditions (with
or without stress), kinds of stress, duration of stress and
its crosstalk with other hormones, growth regulators, and
signaling molecules (Nolan etal. 2019; Yin etal. 2019).
For agricultural crop production, an ideal concentration of
brassilonide ranges from 5 to 50mg per hectare (Khripach
2000). Notably, at a very low dose (nM to mM), BRs can
influence differentplant physiological processes; how-
ever, the responses of plants may even differ within the
narrow range of doses. In cucumber plants, a high con-
centration of BR (0.2–1.0µM 24-epibrassinolide, EBR, a
bioactive BR) suppresses the CO2 assimilation capacity,
whereas a moderate concentration of BR (0.1–0.15µM

Journal of Plant Growth Regulation
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EBR) promotes photosynthesis (Jiang etal. 2012). Simi-
larly, a low dose of BR (0.1µM EBR) facilitates stoma-
tal opening and a high dose of BR (1.0µM EBR) causes
stomatal closure (Xia etal. 2014). Analysis of a number
of studies on BR suggests that the responses of plants to
BR concentrations are largely dependent on the specific
application method, plant species, plant growth stage, and
growth conditions (Ahammed etal. 2014). In the following
sections, we discuss the effects of BRs on plant tolerance
to different abiotic stresses.
Heat Stress andBRs
In recent years, heat stress has appeared as one of the major
abiotic stresses due to climate change (Nolan etal. 2019). It
negatively affects crop production in almost every continent
of the world. Heat stress-induced damages include leaf burn-
ing, abscission and senescence, reduced plant growth (shoot
and root), fruit injuries, and decreased plant productivity
(Bita and Gerats 2013). At the molecular level, accumulation
of BES1 and BZR1 occurs under high temperatures, which
promotes the levels of PHYTOCHROME INTERACTING
FACTOR4 (PIF4) (Martinez etal. 2018). Formation of
PIF4-BES1 heterodimers facilitates BZR1 action on gene
transcription, leading to thermogenic growth. On the other
hand, a decreased accumulation of BRI1 under high tem-
peratures affects BR signaling, resulting in increased root
growth (Martins etal. 2017). Notably, exogenous BR appli-
cation can mitigate the deleterious effects of heat in plants
(Sadura and Janeczko 2018).
Photosynthesis is the most sensitive physiological process
to heat stress (Ahammed etal. 2016). High temperatures
not only reduce net photosynthetic rate but also inhibit pho-
tosynthetic efficiency of photosystem II (PSII) and photo-
chemical activity associated with PSI (Ogweno etal. 2008;
Zhang etal. 2013). In tomato, EBR (0.2µM) pretreatment
can ameliorate high temperature-caused reductions in photo-
synthesis by increasing the activities of antioxidant enzymes
that minimize lipid peroxidation under stress (Ogweno etal.
2008). Interestingly, BR can improve thermotolerance in
both heat tolerant and heat-sensitive genotypes of plants.
For instance, EBR pretreatment considerably improves the
photosynthetic pigment contents, net CO2 assimilation rate,
stomatal conductance, photochemical activity of PSI, and
water-use efficiency of both heat tolerant and heat-sensitive
ecotypes of melon under heat stress (Zhang etal. 2013). In
eggplant, EBR treatment (0.05–0.2µM) alleviates the heat
Fig. 1 Brassinosteroids improve
plant tolerance to a wide range
of abiotic stresses. A large
number of studies have revealed
the stress-protective roles of
exogenous brassinosteroid
application in enhancing plant
tolerance to a variety of abiotic
stresses, such as heat, cold,
freezing, drought, salinity,
heavy metals, pesticides, and
organic pollutants

Journal of Plant Growth Regulation
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stress by increasing antioxidant potential, which eventually
minimizes the accumulation of ROS under high tempera-
tures (Wu etal. 2014). Likewise, foliar application of EBR
(0.01µM) remarkably improves growth, biomass accumu-
lation, photosynthetic efficiency, and antioxidant potential
under high temperature in wheat (Hussain etal. 2019). In
rice, the application of a BR mimic 7,8-Dihydro-8α-20-
hydroxyecdysone (αDHECD, 0.0001µM) in the repro-
ductive stage could increase photosynthesis, carbohydrate
contents, seed setting, and seed weight under heat stress
(Sonjaroon etal. 2018). These reports clearly indicate that
BRs have certain stimulatory effects on plant photosynthe-
sis, and antioxidant capacity which largely contribute to
mitigating deleterious effects of heat stress.
Although a large number of studies demonstrated the heat
stress-protective role of BR using exogenous applications,
only a small number of studies are focused on the in-depth
mechanisms with genetic evidence (Ahammed etal. 2014;
Yu etal. 2004; Zhou etal. 2014). It appears that BRs induce
heat tolerance through a complex mechanism and only a
few pieces of that are currently known. It has been shown
that a transient H2O2 production in the apoplast functions
as a critical signal to mediate BR-induced heat stress toler-
ance in tomato (Zhou etal. 2014). The BR-induced H2O2
production in the apoplast is dependent on NADPH oxidase,
which is encoded by RESPIRATORY BURST OXIDASE
HOMOLOG 1 (RBOH1). When RBOH1, MITOGEN ACTI-
VATED PROTEIN KINASE 2 (MPK2) or MPK1/2 genes are
silenced in tomato plants, H2O2 accumulation is drastically
suppressed and BR-induced tolerance to heat stress is com-
promised (Nie etal. 2013). Notably, the silencing of MPK1
does not result in such effect, suggesting that MPK2 is more
important than MPK1 in BR-induced H2O2 production in
the apoplast and subsequent heat tolerance. The study also
reveals that RBOH1, H2O2, and MPK2 might function in a
positive feedback loop to mediate BR-induced tolerance to
high temperatures (Fig.2). In addition, the transcript lev-
els of the stress response and defense-related genes such
as Cu–Zn SOD, APX5, CAT1, GR1, WRKY1, NPR1, PR1,
and HSP90 are upregulated by exogenous BR application in
tomato, revealing a mechanism of BR-induced heat tolerance
(Zhou etal. 2014).
Besides the antioxidant system, heat-shock proteins
(HSPs) play an important role in BR-induced thermotol-
erance (Dhaubhadel etal. 2002; Kagale etal. 2007). EBR
treatment enhances HSP synthesis by protecting several
components of the translational machinery during extended
heat stress (Dhaubhadel etal. 2002). However, enhanced
expression of HSPs in both det2-1 and dwf4 BR mutants
under heat stress contradicts with those reports and suggests
that HSP accumulation is not necessary for BR-induced
thermotolerance in Arabidopsis (Kagale et al. 2007).
Again, overexpression of BR biosynthetic gene AtDWF4 in
Arabidopsis does not improve stress tolerance in the 5-day-
old seedlings exposed to heat and salt stress. Analysis of
BR mutants in barley that are either BR-deficient (muta-
tions in the HvDWARF or HvCPD) or impaired in BR signal-
ing (missense HvBRI1 gene) shows that all barley mutants
are more tolerant to high temperatures than the wild-type
(Sadura etal. 2019). All these results suggest that the action
modes and physiological effects of endogenous BRs and
exogenously applied BRs are quite diverse in different plant
species (Ahammed etal. 2014; Kagale etal. 2007; Nie etal.
2019).
Cold Stress andBRs
Low temperatures that induce chilling or freezing stress are
a major handicap for crop production in many areas of the
world, particularly in the case of thermophilic plants (Cui
etal. 2011; Zhang etal. 2019b). Cold stress-induced impair-
ments in plants include membrane fluidity modifications,
alterations in macromolecules activities, decreased osmotic
potential in the cells, and also mechanical constraints (Xiong
etal. 2002). Cold stress also affects plant photosynthetic
processes which are manifested by the reduction in the
CO2 assimilation rate, photoinhibition at PSI and PSII, and
decreased enzyme activity of the Benson–Calvin Cycle
(Jiang etal. 2013; Zhang etal. 2019b).
Similar to heat stress, cold stress also induces ROS
accumulation and high levels of ROS can cause damage
Fig. 2 A proposed working model showing the mechanism of brassi-
nosteroid (BR)-induced stress tolerance through the production of
reactive oxygen species (ROS) in the apoplast. Exogenous applica-
tion or endogenous BR manipulation by overexpression of BR bio-
synthetic genes induces the expression of RESPIRATORY BURST
OXIDASE HOMOLOG 1 (RBOH1) encoding NADPH oxidase which
is responsible for ROS production in the apoplast. BR-mediated ROS
signals modulate redox homeostasis, leading to activation of tran-
scription factors (TFs) that control transcription of BR-regulated
and stress-responsive genes to enhance tolerance to abiotic stresses
through the accumulation of protective proteins. Notably, the mito-
gen-activated protein kinase (MAPK) activation plays an important
role in BR-mediated stress tolerance and RBOH1, H2O2 and MPK2
function in a positive feedback loop to mediate BR-induced H2O2
accumulation and subsequent signaling

Journal of Plant Growth Regulation
1 3
to biomembranes through lipid peroxidation (Chen etal.
2013). To avoid excessive ROS accumulation and the over-
reduction of the photosystems that cause photoinhibition,
plants have developed a diverse array of ROS scavenging
and photoprotective strategies, respectively (Fang etal.
2019; Ahammed etal. 2020b; Zhang etal. 2019a). Overex-
pression of genes that encode ROS scavenging enzymes or
mutant plants with an increased ROS scavenging capabil-
ity show better tolerance to cold stress (Xiong etal. 2002).
While BR deficiency attenuates chilling tolerance by induc-
ing protein oxidation and lipid peroxidation, exogenous EBR
application or overexpression of DWRF increases chilling
tolerance by alleviating oxidative damage in tomato plants
(Xia etal. 2018). Notably, ROS can also act as signals in
mediating BR-regulated responses to cold stress tolerance
(Cui etal. 2011). A recent study showed that RBOH1,
GLUTAREDOXIN (GRX), and 2‐cysteine peroxiredoxin
(2‐Cys Prx) participate in a signaling cascade to mediate
BR-induced chilling tolerance in tomato (Xia etal. 2018).
RBOH1 encodes NADPH oxidase which is responsible for
generating ROS in the apoplast, mostly for signaling pur-
poses (Zhou etal. 2014). In addition to ROS, NO partici-
pates in the BR-regulated cold response pathway (Cui etal.
2011). It has been revealed that NO functions downstream of
H2O2 in BR-induced cold tolerance. Exogenous application
of EBR (0.1µM) improves CO2 assimilation and alleviates
the photoinhibition of PSII under cold stress. The recov-
ery of photosynthetic apparatus following BR treatment is
mediated by the activation of key enzymes involved in the
ascorbate–glutathione (AsA-GSH) cycle as well as redox
homeostasis (Jiang etal. 2013). EBR treatment modulates
the component of the AsA-GSH cycle under chilling stress
on a temporal basis leading to enhanced chilling tolerance in
grape (Vitis vinifera) seedlings (Chen etal. 2019). Similarly,
foliar application of EBR (0.3µM) improves tolerance to
chilling stress in grapevines by strengthening the antioxida-
tive potential that minimizes membrane lipid peroxidation
under stress conditions (Xi etal. 2013). In maize, EBR pre-
treatment (1.0µM) can increase plant height, biomass, and
concentration of chlorophyll, protein, and sugar under cold
stress (Singh etal. 2012).
To avoid photoinhibition under cold stress, plants adopt
an important strategy called photoprotection. BRs have been
shown to be involved in photoprotection in plants under
chilling stress. Upon exposure to chilling temperatures,
plants accumulate active BRs and activate BZR1, which
eventually elevate the transcript levels of RBOH1 and apo-
plastic H2O2 production (Fang etal. 2019). On the contrary,
a mutation in BZR1 or suppression of RBOH1 abolishes
BR-induced photoprotection and thus aggravates chilling-
caused photoinhibition. Notably, BRs-induced apoplastic
H2O2 is critical for the PROTON GRADIENT REGULA-
TION5 (PGR5)-dependent cyclic electron flow (CEF) and
subsequent induction of non-photochemical quenching
(NPQ), accumulation of D1 and PSII subunit S (PsbS) pro-
teins, and redox signaling, which greatly contribute to BR-
induced photoprotection under chilling (Fang etal. 2019).
Transcriptome analysis shows that EBR treatment increases
thetranscript levels of chlorophyll biosynthesis and photo-
synthesis-related genes encoding the PSII oxygen-evolving
enhancer protein, PSI subunit, light-harvesting chlorophyll
protein complexes I and II, and ferredoxinunder low tem-
perature (Zhao etal. 2019).
BRs have been shown to enhance freezing tolerance
through both C-REPEAT/DEHYDRATION-RESPONSIVE
ELEMENT BINDING FACTOR1 (CBF1)-dependent and
independent pathways by the activation of COLD-RESPON-
SIVE (COR) genes (Eremina etal. 2017). Moreover, BR-
mediated enhanced cold tolerance involves the accumulation
of BZR1 and BES1 in their unphosphorylated (active) forms,
which promote transcription of CBF1 and CBF2 to induce
cold tolerance (Li etal. 2017). However, BR negatively
regulates cold stress responses during prolonged cold stress
by destabilizing the transcription factor INDUCER OF CBF
EXPRESSION1 (ICE1) by BRASSINOSTEROIDINSENSI-
TIVE2 (BIN2) (Ye etal. 2019). These studies suggest that
BRs can not only promote stress tolerance but also attenuate
stress responses, which largely depend on spatiotemporal
regulation (Nolan etal. 2019).
BRs-induced enhanced tolerance to cold is not limited
to intact plants rather on harvested plant products, such
as fruits. Studies have revealed that BR can improve the
post-harvest quality of vegetables and fruits by extending
the shelf life under low temperature stress (Aghdam and
Mohammadkhani 2014; Wang etal. 2012b). But for the post-
harvest management, relatively high concentrations of EBR
are used compared to the concentrations that are used to con-
fer stress tolerance in the intact plant. For instance, chilling
stress drastically deteriorates the fruit quality in tomatoes
(Li etal. 2016a, b); however, 6µM EBR treatment could
alleviate chilling-induced injuries in tomato fruits, which is
attributed to BR-induced inhibition of phospholipase D and
lipoxygenase activity (Aghdam and Mohammadkhani 2014).
In the case of mango, 10µM EBR treatment protects fruits
from cold-induced injuries by increasing the levels of a set
of proteins such as remorin, abscisic acid stress ripening-
like protein, type II SK2 dehydrin, and temperature-induced
lipocalin (Li etal. 2012a). In addition, BR reduces phase
transition temperature and increases unsaturation degree of
fatty acids in the plasma membrane lipids of mango fruits,
leading to increased fluidity under cold (Li etal. 2012a).
Wang etal. (2012b) examined the effect of different EBR
concentrations on vegetable (Capsicum annuum L.) quality
under low temperature (3°C) and found that 15µM EBR
is the most effective concentration that could ameliorate
chilling-caused damages in fruits of green bell pepper. The

Journal of Plant Growth Regulation
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activity of the antioxidant enzymes and levels of chlorophyll
and l-ascorbic acid were higher in EBR-treated pepper fruits
which potentially minimized lipid peroxidation and electro-
lyte leakage under cold stress.
Drought andBRs
Drought is caused due to the unavailability of the water in
soils (Ahammed etal. 2020a). Lack of rainfall or irrigation
results in the drought that drastically reduces crop productiv-
ity. The problem is more severe in areas with insufficient or
unreliable rainfall. Drought eventually causes osmotic stress
that affects normal cellular activities by disrupting homeo-
stasis and distribution of ions such as uptake, extrusion, and
sequestration of ions in the cells (Xiong and Zhu 2002).
Drought tolerance is closely associated with the accumula-
tion of abscisic acid (ABA). Studies have revealed that exog-
enous BR application can enhance the ABA level and miti-
gate the deleterious effects of drought on plants (Wang etal.
2019b). For instance, in tomato, EBR treatment enhances
tolerance to drought which can be reflected by improved
photosynthetic capacity, leaf water status, and antioxidant
defense under stress conditions (Yuan etal. 2012). In pepper
leaves, exogenous BR treatment (0.02µM) can increase the
efficiency of light utilization and the dissipation of excitation
energy in the PSII antennae under drought (Hu etal. 2013).
In Chorispora bungeana, exogenous BR application (0.1µM
EBR) can enhance tolerance to drought caused by polyethyl-
ene glycol (PEG) treatment (Li etal. 2012b). BR application
alters the expression of genes that encode both structural and
regulatory proteins. For example, EBR-induced increased
transcript levels of BnCBF5 and BnDREB (two key drought
responsive genes) partly contribute to BR-induced enhanced
tolerance to drought in Brassica napus seedlings (Kagale
etal. 2007). Importantly, studies also reveal that BR treat-
ments can alleviate a long term effect of drought on plants.
For instance, Brassica juncea plants that experience week-
long drought stress at the early growth stage show reduced
growth and photosynthetic rate even after 60days. How-
ever, post-drought treatment with 28-homobrassinolide
(HBL, 0.01µM) at 30days after sowing could remarkably
improve both growth and photosynthesis after 60days
of sowing (Fariduddin etal. 2009). While drought stress
induces excessive ROS accumulation, BR treatment can
remarkably reduce the levels of ROS and lipid peroxidation
under drought stress (Yuan etal. 2010). Although the exog-
enous application of BRs improves tolerance to some abiotic
stresses, such as drought, both BR-deficient and insensitive
mutants show enhanced tolerance to stress (Nie etal. 2019;
Nolan etal. 2019; Northey etal. 2016). However, a study on
tomato shows that an elevationin endogenousBR content
but not BR signaling intensity enhances drought tolerance
(Nie etal. 2019). The study also established a negative effect
of BRI1 overexpression on tomato drought tolerance, sug-
gesting that defects in the BR pathway might either increase
or decrease stress tolerance, thus signifying the complex-
ity of the relationships between BRs and stress responses
(Nolan etal. 2019).
Salinity andBRs
Salinity is a major cause of osmotic stress, which is often
termed as physiological drought. It negatively affects
growth, development, and crop yield. BRs have been shown
to mitigate negative effects of salinity in a range of plants
including Arabidopsis (Arabidopsis thaliana), mustard
(Brassica napus), rapeseed (Brassica juncea), eggplant
(Solanum melongena), pepper (Capsicum annuum), cucum-
ber (Cucumis sativus), common bean (Phaseolus vulgaris),
maize (Zea mays), and black locust (Robinia pseudoacacia
L.) (Hayat etal. 2010; Yuan etal. 2012; Yue etal. 2018).
In eggplants, EBR treatment-induced enhanced tolerance to
salt stress is manifested by the increased activity of anti-
oxidant enzymes, decreased Na+ and Cl− concentrations,
and increased K+ and Ca2+ concentrations. Similarly, EBR
application can reduce the concentration of NO3
− and NH4
+ in cucumber plants under salt stress (Yuan etal. 2012). In
rapeseed, foliar application of HBL could effectively ame-
liorate the deleterious effects of salinity stress even at 30
daysas well as 45days after sowing (Hayat etal. 2012b). In
cucumber plants, BR-induced enhanced tolerance to salin-
ity stress is attributed to increased photosynthesis, nitrogen
use efficiency, and total polyamines (Yuan etal. 2012). In
black locust, exogenous EBR application (seed soaking
and root dipping) reduces leaf Na+ content and membrane
leakage and improves the net photosynthetic rate, stomatal
conductance, transpiration rate, chlorophyll content, and
maximum quantum efficiency of PSIIunder salinity stress
(Yue etal. 2018). BR is also effective in mitigating com-
bined stress effects on plants. For instance, EBR (1µM)
can alleviate combined stress induced by NaCl and NiCl2
in Brassica juncea (Ali etal. 2008), and HBL (0.01µM)
can mitigate salt- and high temperature-induced combined
stress in mung bean (Hayat etal. 2010). This large variation
in BR concentrations further highlights the dose–effect of
BR depending on the types of BR and species of plants.
A role for ubiquitin-conjugating enzymes32 (UBC32) has
been revealed in BR-induced tolerance to salt stress (Cui
etal. 2012). As a functional component of the endoplasmic
reticulum-associated protein degradation (ERAD) pathway,
UBC32 influences the accumulation of the BRI1 receptor
in cells and it also directs the ERAD pathway towards BR-
enhanced salinity tolerance in Arabidopsis. Moreover, BR
has been implicated in regulating DNA methylation, which

Journal of Plant Growth Regulation
1 3
plays a vital role in salt tolerance. For instance, seed priming
with EBR induces total methylation and improves salt toler-
ance, suggesting a role for BR in epigenetic modification
under salinity stress (Amraee etal. 2019).
Heavy Metal Stress andBRs
Due to extensive human anthropogenic activities, includ-
ing mining, urbanization, industrialization, and fossil fuel
combustion, pollution caused by multiple heavy metals
has tremendously increased during the last several decades
(Chen etal. 2015; Zhao etal. 2018). Plants grown in pol-
luted soils suffer from metal-induced stress (Ahammed etal.
2013, 2020c; Zhou etal. 2018). Unlike other abiotic stress,
heavy metal-induced stress has some uniqueeffects. Firstly,
crops grown in heavy metal-contaminated soils are com-
promised in terms of yield and quality. Secondly, there are
significant risks associated with the consumption of heavy
metal-contaminated plant products due to potential food
chain contamination (Hasan etal. 2019; Wang etal. 2019c).
Because crops grown in such metal-contaminated soils often
contain high concentrations of toxic metals with additional
risks associated with the consumption of these contami-
nated foods (Hasan etal. 2019). To address these issues, a
large number of studies were conducted involving various
approaches. The use of plant growth regulators, bioactive
compounds, and manipulation of endogenous hormones and
signaling pathways show a huge prospect to alleviate stress
caused by heavy metals (Bucker-Neto etal. 2017; Zhou etal.
2018). Similarly, BRs can mitigate heavy metal stress in a
wide range of plant species (Rajewska etal. 2016; Zhou
etal. 2018).
Heavy metals negatively affect CO2 assimilation capac-
ity and photosynthetic apparatus in plants (Rajewska etal.
2016). Accumulating evidence suggests that heavy metals
such as Cd decrease the photosynthetic process by lim-
iting the utilization of ATP and NADPH in the Calvin
cycle. In tomato, cadmium (Cd) stress (100µM for 40
days) significantly decreased the net photosynthetic rate,
stomatal conductance, the maximal quantum efficiency of
PSII (Fv/Fm), the quantum efficiency of PSII (фPSII), and
photochemical quenching coefficient (qP) (Ahammed etal.
2013). Cd-induced reduction in CO2 assimilation capacity
is positively correlated with the photosynthetic pigment
content and negatively correlated with the Cd accumula-
tion in leaves. As a result, biomass accumulation in plants
is drastically inhibited by Cd stress. However, foliar appli-
cation of EBR (0.1µM) significantly increases biomass
accumulation by improving CO2 assimilation capacity, Fv/
Fm, and photosynthetic pigment content under Cd stress.
Furthermore, exogenous EBR decreases Cd uptake in roots
and its translocation to the leaves. Transmission electron
micrographs of tobacco leaf mesophyll cells showed dis-
torted cell wall and cell membrane, and dilated thylakoid
under chromium (Cr) stress (Bukhari etal. 2016). How-
ever, EBR application protected the Cr-induced damage
to chloroplast and helped to maintain the organization
of grana and thylakoids under Cr stress. Similar to the
EBR, HBL also shows a stress-protective role in mitigat-
ing heavy metal stress. HBL treatment could alleviate the
Cd-induced reduction of growth, photosynthesis, and the
photochemistry of PSII in tomato seedlings (Singh and
Prasad 2017).
At the cellular level, ROS production is triggered upon
exposure of the plants to heavy metals, which negatively
affect plant metabolism causing oxidative injury to proteins,
lipids, and nucleic acids (Song etal. 2012).Interestingly,
heavy metalssuch asnickel (Ni)stimulatethe biosynthe-
sis of different BRs (castasterone, typhasterol, epibrassi-
nolide, and dolicholide) in Brassica juncea L. (Kanwar etal.
2012).BRs have been shown to safeguard plants from heavy
metal-induced stress. For instance, in tomato plants, EBR
treatment (0.1µM) can enhance tolerance to Cd stress by
enhancing photosynthesis, photochemical efficiency of pho-
tosystems, photosynthetic pigment content, and the activity
of key antioxidative- and detoxification-related enzymes at
protein and transcript levels (Ahammed etal. 2013). Simi-
larly, foliar application of BRs (0.01µM EBR or HBL)
can improve tomato fruit yield and quality in ~ 12mgkg−1
Cd-contaminated soils (Hayat etal. 2012a). BRs show a
strong protective effect against Cd stress within a short time
after application. For instance, a single foliar dose of EBR
or HBL (0.01µM) at 24h prior to the measurement can
remarkably improve the photosynthesis in tomato leaves
under 60-day-long Cd stress (Hasan etal. 2011). In legumi-
nous crops, BR treatment improves nodule formation under
heavy metal stress. In Vigna radiata, EBR-induced enhanced
nodulation promotes plant growth under Ni stress. Similarly,
HBL treatment alleviates Cd phytotoxicity by boosting the
levels of enzymatic as well as non-enzymatic antioxidants
in Cicer arietinum (Hasan etal. 2008). Supplementation
of EBR (5nM) in the half-strength MS medium enhances
tolerance of tomato seedlings to ZnO nanoparticle-induced
stress by improving the activity of antioxidant enzymes and
redox poise (Li etal. 2016b). Taken together,exogenous BR-
induced enhancement of tolerance to heavy metals is attrib-
uted to substantial improvement in photosynthetic pigment
content, antioxidative defense (enzymatic and non-enzy-
matic antioxidants), ROS scavenging capacity, glutathione
content, phytochelatins content, and carbon metabolism
under heavy metal stress (Choudhary etal. 2012; Rajewska
etal. 2016).Despite numerous reports supporting the stress-
protective role of BR against heavy metal stress, it remains
unclear whether endogenous BR levels are modulated by
exogenous BR underheavy metal stress.

Journal of Plant Growth Regulation
1 3
Pesticides andBRs
Pesticides are typically organic compounds commonly
used for preventing and controlling pests, such as harmful
insects, plant pathogens (fungi, bacteria, and nematodes),
weeds, and so on (Sharma etal. 2016a, 2019). The appli-
cation of pesticides is an integral part of modern agricul-
ture for sustainable crop production worldwide (Tiwari
etal. 2019). Although pesticides can secure relevant crop
losses up to 80% (Oerke 2005), the rates and amounts of
pesticide application are tremendously high in develop-
ing countries (Liu etal. 2016). Thus, non-judicious and
irrational uses of pesticides can cause phytotoxicity and
human health hazards. Therefore, it is indispensable to
ensure food safety by reducing pesticide residues in edible
plants (Chen etal. 2019).
Plants have the capacity to detoxify or degrade toxic
organic compounds (Zhou et al. 2015). The inher-
ent detoxification mechanisms of plants can be used to
minimize pesticide residues in plants (Hou etal. 2018).
Glutathione-induced detoxification and sequestration of
organic pollutants play a major role in plant tolerance to
pesticides and organicpollutants. Many studies show that
BR can improve plant tolerance to pesticide- and heavy
metal-induced stress (Hou etal. 2018; Xia etal. 2009b;
Yin etal. 2016; Sharma etal. 2016b, c, 2017). Moreover,
BR can reduce pesticide residues in plants by improving
the detoxification pathway. BRs have been considered a
promising, eco-friendly, natural substances, which are
suitable for a wide range of applications to reduce the risks
associated the exposure to pollutants (Hou etal. 2018; Xia
etal. 2009b).
The role of BRs in enhancing plant growth, photosyn-
thesis, and yield is well established (Nolan etal. 2019).
BRs-induced enhanced biomass accumulation is largely
attributed to the BRs-induced improvement in photo-
synthesis (Yu etal. 2004). BRs particularly increase the
gene expression of carbon fixation and initial activity of
RuBiSCO to increase CO2 assimilation in plants (Xia
etal. 2006; Sharma etal. 2019). In addition, BRs improve
photosynthetic electron transfer and overall activity of
photosystem 1 (PS I) and II. However, pesticide appli-
cation drastically reduces the photosynthetic capacity of
plants (Xia etal. 2006). Xia etal (2006) investigated the
effect of nine pesticides (paraquat, cuproxat, imidacloprid,
cyazofamid, haloxyfop, Xuazifop-p-butyl, chlorpyrifos,
Xusilazole, and abamectin) on photosynthesis in cucum-
ber plants. They used practical dosages of these pesticides
to assess phytotoxicity with or without pretreatment with
EBR (Xia etal. 2006). The pesticide application inhibited
the Pn, Gs, Fv/Fm, фPSII , and qP. For instance, chlorpyri-
fos, imidacloprid, and abamectin treatment decreased Pn
by 36, 81, and 40%, respectively. While the imidacloprid
and chlorpyrifos-induced inhibition of CO2 assimilation
was attributed to both stomatal and non-stomatal factors,
the abamectin treatment-induced reduction in Pn was
mainly caused by stomatal factors. However, the pesticide-
induced impairments to photosynthetic apparatus were
alleviated by EBR pretreatment (foliar spray) with a few
exceptions. It has been suggested that EBR could attenuate
the terbutryn (s-triazine group pesticide that reduces the
electron transfer)-induced inhibition on PSII by facilitat-
ing the displacement of QB from its binding site on the D1
protein of PSII.
In another study, when cucumber plants were grown
in chlorpyrifos-contaminated hydroponics solution
(20–80µM), the root elongation rate was drastically inhib-
ited in a dose-dependent manner (Ahammed etal. 2017).
In addition to the inhibitory effects of chlorpyrifos on root
elongation, leaf chlorosis and root browning were observed,
which further confirmed the toxic effects of chlorpyrifos
on plant growth. However, foliar application of EBR alle-
viated chloropyrifos (10µM)-retarded inhibition on the
shoot and root length. The positive effect of EBR on plant
growth increased steadily with the concentrations of EBR
(0.001–0.1µM); however, the 0.1µM EBR exerted the most
remarkable effects, with root elongation promoted by ca.
43% under chloropyrifos treatment (Ahammed etal. 2017).
In mustard (Brassica juncea L.), pre-sowing seed treatment
with EBR enhanced plant growth (length of seedlings and
dry weight) when grown under imidacloprid (a preferred
insecticide to control soil and sap-sucking insects) toxicity
(Sharma etal. 2016c). EBR-induced alleviation of imidaclo-
prid toxicity was closely associated with the EBR-induced
enhancements in shoot length, number of leaves, photo-
synthetic pigment contents, and gas exchange parameters
(Sharma etal. 2016b). A number of studies showed that
BR can protect plants from ROS-induced oxidative stress
by stimulating enzymatic and non-enzymatic antioxidant
defense (Rajewska etal. 2016). Mehler reactions are poten-
tial sources of toxic ROS. EBR-induced enhanced CO2
assimilation serves as an additional electron sink for CO2
reduction which thus diverts undue electrons from alterna-
tive electron sinks, such as Mehler reactions (Hu etal. 2013).
It is well established that EBR could enhance the ROS scav-
enging capacity of plants under both normal and stressful
conditions, which is largely attributed to the enhancement of
antioxidant enzymes. Thus, the capacity of EBR to enhance
both CO2 assimilation and antioxidant enzyme activity
largely contribute to the alleviation of pesticide-induced
phytotoxicity (Xia etal. 2006, 2009a, b).
Pesticide residues remain in the leaf tissues are prin-
cipally removed through in planta detoxification pathway
(Hou etal. 2019). Time-course analysis of pesticide residues
showed that chlorothalonil residue did not decrease after 6

Journal of Plant Growth Regulation
1 3
days of pesticide application (Xia etal. 2009b). BRs have
been implicated in enhancing plant detoxification pathways
towards the reduction of the pesticide residues from the
edible vegetables and fruits. EBR (0.1µM) can decrease
residues of diverse classes of common pesticides such as
organophosphorus, organochlorine, and carbamate pesti-
cides in a range of plant species including tomato, rice, tea,
broccoli, cucumber, and strawberry by 30–70% (Zhou etal.
2015). Even the lowest concentration of EBR (0.02µM)
within the physiological range dramatically decreased the
chlorothelonil residue by 38.9%. Xia etal (2009a, b) showed
that exogenous EBR accelerated the metabolism of multiple
pesticides and consequently reduced the pesticide residues
in cucumber. They found that EBR promoted the activity
of enzymes such as glutathione S-transferase (GST), per-
oxidase (POD), and glutathione reductase (GR) involved
in pesticide metabolism. Moreover, the transcript levels of
genes P450 and MRP encoding P450 monooxygenase and
ABC-type transporter, respectively, were upregulated by
EBR which greatly contributed to the enhanced metabolism
of multiple pesticides such as chlorpyrifos, cypermethrin,
chlorothalonil, and carbendazim (Xia etal. 2006, 2009b).
Exogenous EBR application also stimulates plant second-
ary metabolism by enhancing the transcripts and activity of
secondary metabolism-related enzymes such as phenylala-
nine ammonia-lyase (PAL) and polyphenol oxidase (PPO),
and the concentration of flavonoids, which largely contrib-
ute to alleviate organic pollutant-induced stress (Ahammed
etal. 2013, 2017). A genome-wide microarray analysis in
tomato leaves showed that a total of 301 genes, including a
set of detoxifying genes encoding cytochrome P450, oxi-
doreductase, hydrolase, and transferase were upregulated
by the fungicide chlorothalonil (CHT) and exogenous EBR,
further explaining the role of BR in strengthening xenobi-
otic detoxification capacity (Zhou etal. 2015). Thus, BRs
promote pesticide degradation most likely by increasing glu-
tathione metabolism and GST activity.
BR effects on pesticide metabolism are largely based on
pharmacological evidence. There are a few genetic studies
that untraveled potential mechanisms of BR-induced pes-
ticide detoxification. BR-deficient mutant d^im and the BR
receptor BRI1-silenced tomato plants accumulate 21.7%
and 30.2% higher CHT residues in leaves than that in the
WT plants and the non-silenced (pTRV) plants, respectively
(Zhou etal. 2015). When WT and d^im plants were pre-
treated with exogenous pesticide (CHT), residues decreased
by 31.6% and 58.1%, respectively, suggesting that endog-
enous BR deficiency potentially attenuated pesticide deg-
radation capacity of d^im plants. Meanwhile, EBR-induced
enhanced pesticide metabolism is compromised in BRI1-
silenced tomato plants. Zhou etal (2015) also showed that
apoplastic H2O2 production via RBOH1-encoded NADPH
oxide-dependent pathway plays a critical role in BR-induced
pesticide metabolism. Silencing of RBOH1 in tomato plants
compromises the BR effects on the activity of GST, glu-
tathione biosynthesis, and the redox homeostasis, leading
to increased pesticide residues in tomato leaves. It was
concluded that BRs enhanced pesticide degradation by
increasing glutathione metabolism and GST activity via an
RBOH1-dependent pathway.
Although it has been established that RBOH1-mediated
apoplastic ROS production is essential for the BR-mediated
pesticide metabolism (Zhou etal. 2015), it remains largely
unknown how ROS signals are transduced downstream to
improve pesticide metabolism. A series of ROS-scavenging
enzymes, redox buffers such as glutathione and oxidoreduc-
tases such as glutaredoxins (GRXs), peroxiredoxins (PRXs),
thioredoxins, and peroxidases are involved in sensing the
increased ROS levels in plants (Karl-Josef 2014). Recently,
it has been revealed that GRXS16, a CGFS-type GRX, acts
downstream of apoplastic ROS production and it is involved
in the BR-induced pesticide metabolism in tomato (Hou
etal. 2018). GRXS16 localization has been confirmed in
both the cytosol and nucleus and it is believed that GRXS16
can activate detoxification genes such as GST via interac-
tion with putative transcription factors. Several pieces of
evidence suggest that GRX can interact with transcription
factor TGA2, which participates in plant development,
stress response, and detoxification process (Hou etal. 2018;
Zander etal. 2014). TGA2 factor can directly bind to the
TGACG-motif of the detoxification-related gene GST3, sug-
gesting that BR-induced pesticide metabolism is mediated
by the interaction between GRX and transcription factors,
which triggers the expression of genes involved in pesticide
detoxification (Hou etal. 2019).
Conclusions
Plants need certain environmental cues for their normal
growth and development; however, extreme weather
events, as well as environmental pollution, can negatively
affect crop production. Cellular homeostasis, detoxifi-
cation, and recovery of growth are three major kinds of
responses operated by plants to overcome stress events.
Phytohormone BRs play a crucial role in mediating these
responses by regulating specific sets of genes. BRs have
been shown to regulate the transcription of such genes
that encodes protective proteins vital for stress tolerance
(Fig.2). Although BR effects on plants are less promi-
nent under control (normal) conditions, their beneficial
effects are well recognized under stressful conditions.
BR-induced enhanced stress tolerance is closely associ-
ated with the BR-induced improvement in CO2 assimi-
lation, photoprotection, antioxidant potential (enzymatic
and non-enzymatic), redox homeostasis, ROS scavenging,

Journal of Plant Growth Regulation
1 3
defense response, secondary metabolism, detoxification
potential, and autophagy (Fig.3). Since multiple stressors
often occur under natural conditions, BRs have important
implications on crop production in the face of changing
climate.
Acknowledgements Research in the authors’ laboratories was funded
by the National Natural Science Foundation of China (31950410555),
the National Key Research and Development Program of China
(2018YFD1000800), the National Key R&D Program of China
(2017YFE0107500), and the Zhejiang Provincial Natural Science
Foundation of China (LY19C160009).
Author Contributions Conceived and designed the article: GJA and
XL; wrote the draft manuscript: GJA and XL; and reviewed and edited
the manuscript: GJA, XL, AL, and SC. All authors have read and
approved the manuscript.
Compliance with Ethical Standards
Conflicts of interest The authors declare that they have no conflicts
of interest.
References
Aghdam MS, Mohammadkhani N (2014) Enhancement of chilling
stress tolerance of tomato fruit by postharvest brassinolide
treatment. Food Bioprocess Technol 7(3):909–914. https ://doi.
org/10.1007/s1194 7-013-1165-x
Ahammed GJ, Choudhary SP, Chen S, Xia X, Shi K, Zhou Y, Yu J
(2013) Role of brassinosteroids in alleviation of phenanthrene-
cadmium co-contamination-induced photosynthetic inhibition
and oxidative stress in tomato. J Exp Bot 64(1):199–213. https
://doi.org/10.1093/jxb/ers32 3
Ahammed G, Xia X, Li X, Shi K, Yu J, Zhou Y (2014) Role of brassi-
nosteroid in plant adaptation to abiotic stresses and its interplay
with other hormones. Curr Protein Pept Sci 16(5):462–473
Ahammed GJ, Li X, Zhou J, Zhou Y-H, Yu J-Q (2016) Role of hor-
mones in plant adaptation to heat stress. In: Ahammed G, Yu JQ
(eds) Plant hormones under challenging environmental factors.
Springer, Dordrecht
Ahammed GJ, He BB, Qian XJ, Zhou YH, Shi K, Zhou J, Yu JQ,
Xia XJ (2017) 24-Epibrassinolide alleviates organic pollutants-
retarded root elongation by promoting redox homeostasis and
secondary metabolism in Cucumis sativus L. Environ Pollut
229:922–931. https ://doi.org/10.1016/j.envpo l.2017.07.076
Fig. 3 Different physiological, biochemical, and molecular processes
involved in brassinosteroids (BRs)-induced abiotic stress tolerance
and structures of two most active BRs. BRs promote stress tolerance
by positively modulating multiple cellular processes such as CO2
assimilation, photoprotection, antioxidant defense, redox balance,
reactive oxygen species (ROS) scavenging, ROS signaling, defense
response, detoxification, secondary metabolism, and autophagy in
plants. ATGs autophagy-related genes, CEF cyclic electron flow, D1
the D1 protein of photosystem, GRX glutaredoxin, GSH reduced glu-
tathione, GST glutathione S-transferase, HSPs heat-shock proteins,
NPQ non-photochemical quenching, NPR1 nonexpressor of patho-
genesis-related gene 1, P450 cytochrome P450, PCs phytochelatins,
PAL phenylalanine ammonia-lyase, PPO polyphenol oxidase, PR-
1 pathogenesis-related 1, PsbS photosystem II subunit S, RBOH1
respiratory burst oxidase homolog 1, RuBisCO ribulose-1,5-bis-
phosphate carboxylase/oxygenase, VDE violaxanthin deepoxidase,
WRKY1 WRKY transcription factor

Journal of Plant Growth Regulation
1 3
Ahammed GJ, Li X, Yang Y, Liu C, Zhou G, Wan H, Cheng Y (2020a)
Tomato WRKY81 acts as a negative regulator for drought tol-
erance by modulating guard cell H2O2-mediated stomatal
closure. Environ Exp Bot. https ://doi.org/10.1016/j.envex
pbot.2019.10396 0
Ahammed GJ, Wang Y, Mao Q, Wu M, Yan Y, Ren J, Wang X, Liu
A, Chen S (2020b) Dopamine alleviates bisphenol A-induced
phytotoxicity by enhancing antioxidant and detoxification poten-
tial in cucumber. Environ Pollut. https ://doi.org/10.1016/j.envpo
l.2020.11395 7
Ahammed GJ, Wu M, Wang Y, Yan Y, Mao Q, Ren J, Ma R, Liu A,
Chen S (2020c) Melatonin alleviates iron stress by improving
iron homeostasis, antioxidant defense and secondary metabolism
in cucumber. Sci Hortic 265:109205
Ali B, Hayat S, Fariduddin Q, Ahmad A (2008) 24-Epibrassinolide
protects against the stress generated by salinity and nickel in
Brassica juncea. Chemosphere 72(9):1387–1392. https ://doi.
org/10.1016/j.chemo spher e.2008.04.012
Amraee L, Rahmani F, Abdollahi Mandoulakani B (2019) 24-Epi-
brassinolide alters DNA cytosine methylation of Linum usitatis-
simum L. under salinity stress. Plant Physiol Biochem 139:478–
484. https ://doi.org/10.1016/j.plaph y.2019.04.010
Bita C, Gerats T (2013) Plant tolerance to high temperature in a chang-
ing environment: scientific fundamentals and production of heat
stress-tolerant crops. Front Plant Sci. https ://doi.org/10.3389/
fpls.2013.00273
Bucker-Neto L, Paiva ALS, Machado RD, Arenhart RA, Margis-Pin-
heiro M (2017) Interactions between plant hormones and heavy
metals responses. Genet Mol Biol 40(1 suppl 1):373–386. https
://doi.org/10.1590/1678-4685-GMB-2016-0087
Bukhari SA, Wang R, Wang W, Ahmed IM, Zheng W, Cao F (2016)
Genotype-dependent effect of exogenous 24-epibrassinolide
on chromium-induced changes in ultrastructure and phys-
icochemical traits in tobacco seedlings. Environ Sci Pollut
Res Int 23(18):18229–18238. https ://doi.org/10.1007/s1135
6-016-7017-2
Chen S, Jin W, Liu A, Zhang S, Liu D, Wang F, Lin X, He C (2013)
Arbuscular mycorrhizal fungi (AMF) increase growth and sec-
ondary metabolism in cucumber subjected to low temperature
stress. Sci Hortic 160:222–229. https ://doi.org/10.1016/j.scien
ta.2013.05.039
Chen C, Zhang H, Wang A, Lu M, Shen Z, Lian C (2015) Phenotypic
plasticity accounts for most of the variation in leaf manganese
concentrations in Phytolacca americana growing in manganese-
contaminated environments. Plant Soil 396(1–2):215–227. https
://doi.org/10.1007/s1110 4-015-2581-7
Chen Z-Y, Wang Y-T, Pan X-B, Xi Z-M (2019) Amelioration of
cold-induced oxidative stress by exogenous 24-epibrassinolide
treatment in grapevine seedlings: toward regulating the ascor-
bate–glutathione cycle. Sci Hortic 244:379–387. https ://doi.
org/10.1016/j.scien ta.2018.09.062
Choe S (2010) Brassinosteroid biosynthesis and metabolism. In:
Davies PJ (ed) Plant hormones: biosynthesis, signal transduc-
tion, action!. Springer, Dordrecht, pp 156–178
Choudhary SP, Yu J-Q, Yamaguchi-Shinozaki K, Shinozaki K, Tran
L-SP (2012) Benefits of brassinosteroid crosstalk. Trends
Plant Sci 17(10):594–605. https ://doi.org/10.1016/j.tplan
ts.2012.05.012
Clouse SD (2015) A history of brassinosteroid research from 1970
through 2005: thirty-five years of phytochemistry, physiology,
genes, and mutants. J Plant Growth Regul 34(4):828–844. https
://doi.org/10.1007/s0034 4-015-9540-7
Cui J-X, Zhou Y-H, Ding J-G, Xia X-J, Shi K, Chen S-C, Asami
T, Chen Z, Yu J-Q (2011) Role of nitric oxide in hydrogen
peroxide-dependent induction of abiotic stress tolerance by
brassinosteroids in cucumber. Plant Cell Environ 34(2):347–358.
https ://doi.org/10.1111/j.1365-3040.2010.02248 .x
Cui F, Liu L, Zhao Q, Zhang Z, Li Q, Lin B, Wu Y, Tang S, Xie Q
(2012) Arabidopsis ubiquitin conjugase UBC32 Is an ERAD
component that functions in brassinosteroid-mediated salt stress
tolerance. Plant Cell 24(1):233–244. https ://doi.org/10.1105/
tpc.111.09306 2
Dhaubhadel S, Browning KS, Gallie DR, Krishna P (2002) Brassi-
nosteroid functions to protect the translational machinery and
heat-shock protein synthesis following thermal stress. Plant J
29(6):681–691. https ://doi.org/10.1046/j.1365-313X.2002.01257
.x
Divi UK, Krishna P (2009) Brassinosteroid: a biotechnological target
for enhancing crop yield and stress tolerance. New Biotechnol
26(3–4):131–136. https ://doi.org/10.1016/j.nbt.2009.07.006
Eremina M, Unterholzner SJ, Rathnayake AI, Castellanos M, Khan
M, Kugler KG, May ST, Mayer KFX, Rozhon W, Poppenberger
B (2017) Brassinosteroids participate in the control of basal and
acquired freezing tolerance of plants (vol 113, pg E5982, 2016).
Proc Natl Acad Sci USA 114(6):E1038–E1039
Fang P, Yan M, Chi C, Wang M, Zhou YH, Zhou J, Shi K, Xia X, Foyer
CH, Yu J (2019) Brassinosteroids act as a positive regulator of
photoprotection in response to chilling stress. Plant Physiol. https
://doi.org/10.1104/pp.19.00088
Fariduddin Q, Khanam S, Hasan SA, Ali B, Hayat S, Ahmad A (2009)
Effect of 28-homobrassinolide on the drought stress-induced
changes in photosynthesis and antioxidant system of Bras-
sica juncea L. Acta Physiol Plant 31(5):889–897. https ://doi.
org/10.1007/s1173 8-009-0302-7
Guo DL, Wang ZG, Li Q, Gu SC, Zhang GH, Yu YH (2019) Hydro-
gen peroxide treatment promotes early ripening of Kyoho grape.
Aust J Grape Wine Res 25(3):357–362. https ://doi.org/10.1111/
ajgw.12399
Hasan MK, Ahammed GJ, Sun SC, Li MQ, Yin HQ, Zhou J (2019)
Melatonin inhibits cadmium translocation and enhances plant
tolerance by regulating sulfur uptake and assimilation in Solanum
lycopersicum L. J Agric Food Chem 67(38):10563–10576. https
://doi.org/10.1021/acs.jafc.9b024 04
Hasan SA, Hayat S, Ahmad A (2011) Brassinosteroids protect pho-
tosynthetic machinery against the cadmium induced oxidative
stress in two tomato cultivars. Chemosphere 84(10):1446–1451.
https ://doi.org/10.1016/j.chemo spher e.2011.04.047
Hasan SA, Hayat S, Ali B, Ahmad A (2008) 28-Homobrassinolide
protects chickpea (Cicer arietinum) from cadmium toxicity by
stimulating antioxidants. Environ Pollut 151(1):60–66. https ://
doi.org/10.1016/j.envpo l.2007.03.006
Hayat S, Hasan SA, Yusuf M, Hayat Q, Ahmad A (2010) Effect of
28-homobrassinolide on photosynthesis, fluorescence and anti-
oxidant system in the presence or absence of salinity and tem-
perature in Vigna radiata. Environ Exp Bot 69(2):105–112. https
://doi.org/10.1016/j.envex pbot.2010.03.004
Hayat S, Alyemeni MN, Hasan SA (2012a) Foliar spray of brassi-
nosteroid enhances yield and quality of Solanum lycopersicum
under cadmium stress. Saudi J Biol Sci 19(3):325–335. https ://
doi.org/10.1016/j.sjbs.2012.03.005
Hayat S, Maheshwari P, Wani AS, Irfan M, Alyemeni MN, Ahmad A
(2012b) Comparative effect of 28 homobrassinolide and sali-
cylic acid in the amelioration of NaCl stress in Brassica juncea
L. Plant Physiol Biochem 53:61–68. https ://doi.org/10.1016/j.
plaph y.2012.01.011
Hou J, Zhang Q, Zhou Y, Ahammed GJ, Zhou Y, Yu J, Fang H, Xia X
(2018) Glutaredoxin GRXS16 mediates brassinosteroid-induced
apoplastic H2O2 production to promote pesticide metabolism in
tomato. Environ Pollut 240:227–234. https ://doi.org/10.1016/j.
envpo l.2018.04.120

Journal of Plant Growth Regulation
1 3
Hou J, Sun Q, Li J, Ahammed GJ, Yu J, Fang H, Xia X (2019) Glu-
taredoxin S25 and its interacting TGACG motif-binding factor
TGA2 mediate brassinosteroid-induced chlorothalonil metabo-
lism in tomato plants. Environ Pollut. https ://doi.org/10.1016/j.
envpo l.2019.11325 6
Hu W-h, Yan X-h, Xiao Y-a, Zeng J-j, Qi H-j, Ogweno JO (2013)
24-Epibrassinosteroid alleviate drought-induced inhibition of
photosynthesis in Capsicum annuum. Sci Hortic 150:232–237.
https ://doi.org/10.1016/j.scien ta.2012.11.012
Hussain M, Khan TA, Yusuf M, Fariduddin Q (2019) Silicon-medi-
ated role of 24-epibrassinolide in wheat under high-temperature
stress. Environ Sci Pollut Res 26(17):17163–17172. https ://doi.
org/10.1007/s1135 6-019-04938 -0
Jiang Y-P, Cheng F, Zhou Y-H, Xia X-J, Mao W-H, Shi K, Chen Z,
Yu J-Q (2012) Cellular glutathione redox homeostasis plays an
important role in the brassinosteroid-induced increase in CO2
assimilation in Cucumis sativus. New Phytol 194(4):932–943.
https ://doi.org/10.1111/j.1469-8137.2012.04111 .x
Jiang YP, Huang LF, Cheng F, Zhou YH, Xia XJ, Mao WH, Shi K,
Yu JQ (2013) Brassinosteroids accelerate recovery of photo-
synthetic apparatus from cold stress by balancing the electron
partitioning, carboxylation and redox homeostasis in cucum-
ber. Physiol Plantarum 148(1):133–145. https ://doi.org/10.111
1/j.1399-3054.2012.01696 .x
Kagale S, Divi UK, Krochko JE, Keller WA, Krishna P (2007) Brassi-
nosteroid confers tolerance in Arabidopsis thaliana and Brassica
napus to a range of abiotic stresses. Planta 225(2):353–364. https
://doi.org/10.1007/s0042 5-006-0361-6
Kanwar MK, Bhardwaj R, Arora P, Chowdhary SP, Sharma P, Kumar
S (2012) Plant steroid hormones produced under Ni stress are
involved in the regulation of metal uptake and oxidative stress
in Brassica juncea L. Chemosphere 86(1):41–49. https ://doi.
org/10.1016/j.chemo spher e.2011.08.048
Karl-Josef D (2014) Redox regulation of transcription factors in plant
stress acclimation and development. Antioxid Redox Signal
21(9):1356–1372. https ://doi.org/10.1089/ars.2013.5672
Khripach V (2000) Twenty years of brassinosteroids: steroidal plant
hormones warrant better crops for the XXI century. Ann Bot
86(3):441–447. https ://doi.org/10.1006/anbo.2000.1227
Li B, Zhang C, Cao B, Qin G, Wang W, Tian S (2012a) Brassinolide
enhances cold stress tolerance of fruit by regulating plasma mem-
brane proteins and lipids. Amino Acids 43(6):2469–2480. https
://doi.org/10.1007/s0072 6-012-1327-6
Li YH, Liu YJ, Xu XL, Jin M, An LZ, Zhang H (2012b) Effect of
24-epibrassinolide on drought stress-induced changes in
Chorispora bungeana. Biol Plant 56(1):192–196. https ://doi.
org/10.1007/s1053 5-012-0041-2
Li P, Yin F, Song L, Zheng X (2016a) Alleviation of chilling injury in
tomato fruit by exogenous application of oxalic acid. Food Chem
202:125–132. https ://doi.org/10.1016/j.foodc hem.2016.01.142
Li MQ, Ahammedl GJ, Li CX, Bao X, Yu JQ, Huang CL, Yin HQ,
Zhou J (2016b) Brassinosteroid ameliorates zinc oxide nanopar-
ticles-induced oxidative stress by improving antioxidant potential
and redox homeostasis in tomato seedling. Front Plant Sci 7:13.
https ://doi.org/10.3389/fpls.2016.00615
Li H, Ye K, Shi Y, Cheng J, Zhang X, Yang S (2017) BZR1 Positively
regulates freezing tolerance via CBF-dependent and CBF-inde-
pendent pathways in arabidopsis. Mol Plant 10(4):545–559. https
://doi.org/10.1016/j.molp.2017.01.004
Liu S, Che Z, Chen G (2016) Multiple-fungicide resistance to car-
bendazim, diethofencarb, procymidone, and pyrimethanil in
field isolates of Botrytis cinerea from tomato in Henan Prov-
ince, China. Crop Prot 84:56–61. https ://doi.org/10.1016/j.cropr
o.2016.02.012
Martinez C, Espinosa-Ruiz A, de Lucas M, Bernardo-Garcia S, Franco-
Zorrilla JM, Prat S (2018) PIF4-induced BR synthesis is critical
to diurnal and thermomorphogenic growth. EMBO J. https ://doi.
org/10.15252 /embj.20189 9552
Martins S, Montiel-Jorda A, Cayrel A, Huguet S, Roux CP, Ljung
K, Vert G (2017) Brassinosteroid signaling-dependent root
responses to prolonged elevated ambient temperature. Nat Com-
mun 8(1):309. https ://doi.org/10.1038/s4146 7-017-00355 -4
Nie S, Huang S, Wang S, Mao Y, Liu J, Ma R, Wang X (2019)
Enhanced brassinosteroid signaling intensity via SlBRI1 over-
expression negatively regulates drought resistance in a manner
opposite of that via exogenous BR application in tomato. Plant
Physiol Biochem 138:36–47. https ://doi.org/10.1016/j.plaph
y.2019.02.014
Nie WF, Wang MM, Xia XJ, Zhou YH, Shi K, Chen Z, Yu JQ (2013)
Silencing of tomato RBOH1 and MPK2 abolishes brassinoster-
oid-induced H(2)O(2) generation and stress tolerance. Plant Cell
Environ 36(4):789–803. https ://doi.org/10.1111/pce.12014
Nolan T, Vukasinovic N, Liu D, Russinova E, Yin Y (2019) Brassinos-
teroids: multi-dimensional regulators of plant growth, develop-
ment, and stress responses. Plant Cell. https ://doi.org/10.1105/
tpc.19.00335
Northey JGB, Liang S, Jamshed M, Deb S, Foo E, Reid JB, McCourt
P, Samuel MA (2016) Farnesylation mediates brassinosteroid
biosynthesis to regulate abscisic acid responses. Nat Plants. https
://doi.org/10.1038/nplan ts.2016.114
Oerke EC (2005) Crop losses to pests. J Agric Sci 144(1):31–43. https
://doi.org/10.1017/s0021 85960 50057 08
Ogweno JO, Song XS, Shi K, Hu WH, Mao WH, Zhou YH, Yu JQ,
Nogués S (2008) Brassinosteroids alleviate heat-induced inhibi-
tion of photosynthesis by increasing carboxylation efficiency and
enhancing antioxidant systems in Lycopersicon esculentum. J
Plant Growth Regul 27(1):49–57. https ://doi.org/10.1007/s0034
4-007-9030-7
Peres A, Soares JS, Tavares RG, Righetto G, Zullo MAT, Mandava
NB, Menossi M (2019) Brassinosteroids, the sixth class of phy-
tohormones: a molecular view from the discovery to hormonal
interactions in plant development and stress adaptation. Int J Mol
Sci. https ://doi.org/10.3390/ijms2 00203 31
Planas-Riverola A, Gupta A, Betegon-Putze I, Bosch N, Ibanes M,
Cano-Delgado AI (2019) Brassinosteroid signaling in plant
development and adaptation to stress. Development. https ://doi.
org/10.1242/dev.15189 4
Rajewska I, Talarek M, Bajguz A (2016) Brassinosteroids and response
of plants to heavy metals action. Front Plant Sci 7:629. https ://
doi.org/10.3389/fpls.2016.00629
Sadura I, Janeczko A (2018) Physiological and molecular mechanisms
of brassinosteroid-induced tolerance to high and low tempera-
ture in plants. Biol Plant 62(4):601–616. https ://doi.org/10.1007/
s1053 5-018-0805-4
Sadura I, Pociecha E, Dziurka M, Oklestkova J, Novak O, Gruszka D,
Janeczko A (2019) Mutations in the HvDWARF, HvCPD and
HvBRI1 genes-involved in brassinosteroid biosynthesis/signal-
ling: altered photosynthetic efficiency, hormonal homeostasis
and tolerance to high/low temperatures in barley. J Plant Growth
Regul 38(3):1062–1081. https ://doi.org/10.1007/s0034 4-019-
09914 -z
Sasse JM (2003) Physiological actions of brassinosteroids: an update.
J Plant Growth Regul 22(4):276–288. https ://doi.org/10.1007/
s0034 4-003-0062-3
Sharma A, Bhardwaj R, Kumar V, Thukral AK (2016a) GC-MS stud-
ies reveal stimulated pesticide detoxification by brassinolide
application in Brassica juncea L. plants. Environ Sci Pol-
lut Res 23(14):14518–14525. https ://doi.org/10.1007/s1135
6-016-6650-0
Sharma A, Kumar V, Singh R, Thukral AK, Bhardwaj R (2016b) Effect
of seed pre-soaking with 24-epibrassinolide on growth and pho-
tosynthetic parameters of Brassica juncea L. in imidacloprid soil.

Journal of Plant Growth Regulation
1 3
Ecotoxicol Environ Saf 133:195–201. https ://doi.org/10.1016/j.
ecoen v.2016.07.008
Sharma A, Thakur S, Kumar V, Kanwar MK, Kesavan AK, Thukral
AK, Bhardwaj R, Alam P, Ahmad P (2016c) Pre-sowing seed
treatment with 24-epibrassinolide ameliorates pesticide stress
in Brassica juncea L. through the modulation of stress markers.
Front Plant Sci. https ://doi.org/10.3389/fpls.2016.01569
Sharma A, Thakur S, Kumar V, Kesavan AK, Thukral AK, Bhardwaj R
(2017) 24-epibrassinolide stimulates imidacloprid detoxification
by modulating the gene expression of Brassica juncea L. BMC
Plant Biol 17(1):56. https ://doi.org/10.1186/s1287 0-017-1003-9
Sharma A, Yuan H, Kumar V, Ramakrishnan M, Kohli SK, Kaur
R, Thukral AK, Bhardwaj R, Zheng B (2019) Castasterone
attenuates insecticide induced phytotoxicity in mustard. Eco-
toxicol Environ Saf 179:50–61. https ://doi.org/10.1016/j.ecoen
v.2019.03.120
Singh I, Kumar U, Singh SK, Gupta C, Singh M, Kushwaha SR (2012)
Physiological and biochemical effect of 24-epibrassinoslide
on cold tolerance in maize seedlings. Physiol Mol Biol Plants
18(3):229–236. https ://doi.org/10.1007/s1229 8-012-0122-x
Singh S, Prasad SM (2017) Effects of 28-homobrassinoloid on key
physiological attributes of Solanum lycopersicum seedlings
under cadmium stress: photosynthesis and nitrogen metabolism.
Plant Growth Regul 82(1):161–173. https ://doi.org/10.1007/
s1072 5-017-0248-5
Song Y, Cui J, Zhang H, Wang G, Zhao F-J, Shen Z (2012) Prot-
eomic analysis of copper stress responses in the roots of two rice
(Oryza sativa L.) varieties differing in Cu tolerance. Plant Soil
366(1–2):647–658. https ://doi.org/10.1007/s1110 4-012-1458-2
Sonjaroon W, Jutamanee K, Khamsuk O, Thussagunpanit J, Kaveeta
L, Suksamrarn A (2018) Impact of brassinosteroid mimic on
photosynthesis, carbohydrate content and rice seed set at repro-
ductive stage under heat stress. Agric Nat Resour. https ://doi.
org/10.1016/j.anres .2018.09.001
Tiwari B, Kharwar S, Tiwari DN (2019) Pesticides and rice agricul-
ture. In: Mishra AK, Tiwari DN, Rai AN (eds) Cyanobacteria.
Academic Press, London, pp 303–325
Tong H, Chu C (2018) Functional specificities of brassinosteroid and
potential utilization for crop improvement. Trends Plant Sci.
https ://doi.org/10.1016/j.tplan ts.2018.08.007
Wang B, Li Y, Zhang WH (2012a) Brassinosteroids are involved in
response of cucumber (Cucumis sativus) to iron deficiency. Ann
Bot 110(3):681–688. https ://doi.org/10.1093/aob/mcs12 6
Wang Q, Ding T, Gao L, Pang J, Yang N (2012b) Effect of brassinolide
on chilling injury of green bell pepper in storage. Sci Hortic
144:195–200. https ://doi.org/10.1016/j.scien ta.2012.07.018
Wang Y, Cao JJ, Wang KX, Xia XJ, Shi K, Zhou YH, Yu JQ, Zhou J
(2018) BZR1 mediates brassinosteroid-induced autophagy and
nitrogen starvation tolerance in tomato. Plant Physiol. https ://doi.
org/10.1104/pp.18.01028
Wang FH, Ahammed GJ, Li GY, Bai PT, Jiang Y, Wang SX, Chen SC
(2019a) Ethylene is involved in red light-induced anthocyanin
biosynthesis in cabbage (Brassica oleracea). Int J Agric Biol
21(5):955–963. https ://doi.org/10.17957 /ijab/15.0980
Wang Y-T, Chen Z-Y, Jiang Y, Duan B-B, Xi Z-M (2019b) Involvement
of ABA and antioxidant system in brassinosteroid-induced water
stress tolerance of grapevine (Vitis vinifera L.). Sci Hortic. https
://doi.org/10.1016/j.scien ta.2019.10859 6
Wang JC, Zhu HL, Zhang C, Wang HW, Yang ZJ, Liu ZP (2019c)
Puerarin protects rat liver and kidney against cadmium-induced
oxidative stress. Indian J Anim Sci 89(9):927–931
Wu CY, Trieu A, Radhakrishnan P, Kwok SF, Harris S, Zhang K, Wang
J, Wan J, Zhai H, Takatsuto S, Matsumoto S, Fujioka S, Feld-
mann KA, Pennell RI (2008) Brassinosteroids regulate grain fill-
ing in rice. Plant Cell 20(8):2130–2145. https ://doi.org/10.1105/
tpc.107.05508 7
Wu X, Yao X, Chen J, Zhu Z, Zhang H, Zha D (2014) Brassinoster-
oids protect photosynthesis and antioxidant system of eggplant
seedlings from high-temperature stress. Acta Physiol Plant
36(2):251–261. https ://doi.org/10.1007/s1173 8-013-1406-7
Xi ZM, Wang ZZ, Fang YL, Hu ZY, Hu Y, Deng MM, Zhang ZW
(2013) Effects of 24-epibrassinolide on antioxidation defense
and osmoregulation systems of young grapevines (V-vinifera
L.) under chilling stress. Plant Growth Regul 71(1):57–65.
https ://doi.org/10.1007/s1072 5-013-9809-4
Xia XJ, Huang YY, Wang L, Huang LF, Yu YL, Zhou YH, Yu JQ
(2006) Pesticides-induced depression of photosynthesis was
alleviated by 24-epibrassinolide pretreatment in Cucumis
sativus L. Pestic Biochem Physiol 86(1):42–48. https ://doi.
org/10.1016/j.pestb p.2006.01.005
Xia X-J, Gao C-J, Song L-X, Zhou Y-H, Shi K, Yu J-Q (2014) Role
of H2O2 dynamics in brassinosteroid-induced stomatal closure
and opening in Solanum lycopersicum. Plant Cell Environ
37(9):2036–2050. https ://doi.org/10.1111/pce.12275
Xia XJ, Fang PP, Guo X, Qian XJ, Zhou J, Shi K, Zhou YH, Yu JQ
(2018) Brassinosteroid-mediated apoplastic H2O2-glutaredoxin
12/14 cascade regulates antioxidant capacity in response to
chilling in tomato. Plant Cell Environ 41(5):1052–1064. https
://doi.org/10.1111/pce.13052
Xia XJ, Wang YJ, Zhou YH, Tao Y, Mao WH, Shi K, Asami T,
Chen Z, Yu JQ (2009a) Reactive oxygen species are involved
in brassinosteroid-induced stress tolerance in cucumber. Plant
Physiol 150(2):801–814. https ://doi.org/10.1104/pp.109.13823
0
Xia XJ, Zhang Y, Wu JX, Wang JT, Zhou YH, Shi K, Yu YL, Yu JQ
(2009b) Brassinosteroids promote metabolism of pesticides in
cucumber. J Agric Food Chem 57(18):8406–8413. https ://doi.
org/10.1021/jf901 915a
Xia XJ, Zhou YH, Ding J, Shi K, Asami T, Chen Z, Yu JQ (2011)
Induction of systemic stress tolerance by brassinosteroid in
Cucumis sativus. New Phytol 191(3):706–720. https ://doi.org/
10.1111/j.1469-8137.2011.03745 .x
Xiong L, Zhu J-K (2002) Molecular and genetic aspects of plant
responses to osmotic stress. Plant Cell Environ 25(2):131–139.
https ://doi.org/10.1046/j.1365-3040.2002.00782 .x
Xiong LM, Schumaker KS, Zhu JK (2002) Cell signaling during cold,
drought, and salt stress. Plant Cell 14:S165–S183. https ://doi.
org/10.1105/tpc.00059 6
Ye K, Li H, Ding Y, Shi Y, Song C, Gong Z, Yang S (2019) BRASSI-
NOSTEROID-INSENSITIVE2 negatively regulates the stability
of transcription factor ICE1 in response to cold stress in arabi-
dopsis. Plant Cell 31(11):2682–2696. https ://doi.org/10.1105/
tpc.19.00058
Yin Y-L, Zhou Y, Zhou Y-H, Shi K, Zhou J, Yu Y, Yu J-Q, Xia X-J
(2016) Interplay between mitogen-activated protein kinase and
nitric oxide in brassinosteroid-induced pesticide metabolism in
Solanum lycopersicum. J Hazard Mater 316:221–231. https ://doi.
org/10.1016/j.jhazm at.2016.04.070
Yin W, Dong N, Niu M, Zhang X, Li L, Liu J, Liu B, Tong H (2019)
Brassinosteroid-regulated plant growth and development and
gene expression in soybean. Crop J 7(3):411–418. https ://doi.
org/10.1016/j.cj.2018.10.003
Yu JQ, Huang LF, Hu WH, Zhou YH, Mao WH, Ye SF, Nogues S
(2004) A role for brassinosteroids in the regulation of photosyn-
thesis in Cucumis sativus. J Exp Bot 55(399):1135–1143. https
://doi.org/10.1093/jxb/erh12 4
Yuan G-F, Jia C-G, Li Z, Sun B, Zhang L-P, Liu N, Wang Q-M (2010)
Effect of brassinosteroids on drought resistance and abscisic
acid concentration in tomato under water stress. Sci Hortic
126(2):103–108. https ://doi.org/10.1016/j.scien ta.2010.06.014
Yuan L, Yuan Y, Du J, Sun J, Guo S (2012) Effects of 24-epibrassi-
nolide on nitrogen metabolism in cucumber seedlings under

Journal of Plant Growth Regulation
1 3
Ca(NO3)2 stress. Plant Physiol Biochem 61:29–35. https ://doi.
org/10.1016/j.plaph y.2012.09.004
Yue J, You Y, Zhang L, Fu Z, Wang J, Zhang J, Guy RD (2018) Exoge-
nous 24-epibrassinolide alleviates effects of salt stress on chloro-
plasts and photosynthesis in Robinia pseudoacacia L. seedlings.
J Plant Growth Regul 38(2):669–682. https ://doi.org/10.1007/
s0034 4-018-9881-0
Zander M, Thurow C, Gatz C (2014) TGA transcription factors activate
the salicylic acid-suppressible branch of the ethylene-induced
defense program by regulating ORA59 expression. Plant Physiol
165(4):1671–1683. https ://doi.org/10.1104/pp.114.24336 0
Zhang YP, Zhu XH, Ding HD, Yang SJ, Chen YY (2013) Foliar appli-
cation of 24-epibrassinolide alleviates high-temperature-induced
inhibition of photosynthesis in seedlings of two melon cultivars.
Photosynthetica 51(3):341–349. https ://doi.org/10.1007/s1109
9-013-0031-4
Zhang Y, Liang Y, Zhao X, Jin X, Hou L, Shi Y, Ahammed GJ (2019a)
Silicon compensates phosphorus deficit-induced growth inhibi-
tion by improving photosynthetic capacity, antioxidant potential,
and nutrient homeostasis in tomato. Agronomy 9(11):733
Zhang Z, Wu P, Zhang W, Yang Z, Liu H, Ahammed GJ, Cui J (2019b)
Calcium is involved in exogenous NO-induced enhancement
of photosynthesis in cucumber (Cucumis sativus L.) seedlings
under low temperature. Sci Hortic. https ://doi.org/10.1016/j.scien
ta.2019.10895 3
Zhao B, Li J (2012) Regulation of brassinosteroid biosynthesis and
inactivation F. J Integr Plant Biol 54(10):746–759. https ://doi.
org/10.1111/j.1744-7909.2012.01168 .x
Zhao Z, Jin R, Fang D, Wang H, Dong Y, Xu R, Jiang J (2018) Paddy
cultivation significantly alters the forms and contents of Fe
oxides in an Oxisol and increases phosphate mobility. Soil Till-
age Res 184:176–180. https ://doi.org/10.1016/j.still .2018.07.012
Zhao M, Yuan L, Wang J, Xie S, Zheng Y, Nie L, Zhu S, Hou J,
Chen G, Wang C (2019) Transcriptome analysis reveals a posi-
tive effect of brassinosteroids on the photosynthetic capacity of
wucai under low temperature. BMC Genomics 20(1):810. https
://doi.org/10.1186/s1286 4-019-6191-2
Zhou J, Wang J, Li X, Xia XJ, Zhou YH, Shi K, Chen Z, Yu JQ (2014)
H2O2 mediates the crosstalk of brassinosteroid and abscisic acid
in tomato responses to heat and oxidative stresses. J Exp Bot
65(15):4371–4383. https ://doi.org/10.1093/jxb/eru21 7
Zhou Y, Xia X, Yu G, Wang J, Wu J, Wang M, Yang Y, Shi K, Yu Y,
Chen Z, Gan J, Yu J (2015) Brassinosteroids play a critical role
in the regulation of pesticide metabolism in crop plants. Sci Rep
5:9018. https ://doi.org/10.1038/srep0 9018
Zhou YL, Huo SF, Wang LT, Meng JF, Zhang ZW, Xi ZM (2018)
Exogenous 24-Epibrassinolide alleviates oxidative damage
from copper stress in grape (Vitis vinifera L.) cuttings. Plant
Physiol Biochem 130:555–565. https ://doi.org/10.1016/j.plaph
y.2018.07.029
Zhou Y, Guang Y, Li J, Wang F, Ahammed GJ, Yang Y (2019) The
CYP74 gene family in watermelon: genome-wide identification
and expression profiling under hormonal stress and root-knot
nematode infection. Agronomy 9(12):872
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