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Salinity stress is one of the major abiotic constraints that limit plant growth and yield, which thereby is a serious concern to world food security. It adversely affects crop production by inducing hyperosmotic stress and ionic toxicity as well as secondary stresses such as oxidative stress, all of which disturb optimum physiology and metabolism. Nonetheless, various strategies have been employed to improve salt tolerance in crop plants, among which the application of Melatonin (Mel) could also be used as it has demonstrated promising results. The ongoing experimental evidence revealed that Mel is a pleiotropic signaling molecule, which besides being involved in various growth and developmental processes also mediates environmental stress responses. The current review systematically discusses and summarizes how Mel mediates the response of plants under salt stress and could optimize the balance between plant growth performances and stress responses. Specifically, it covers the latest advances of Mel in fine-tuning the signaling in plants. Furthermore, it highlights plant-built tolerance of salt stress by manifesting the biosynthesis of Mel, its cross talks with nitric oxide (NO), and Mel as a multifaceted antioxidant molecule.

In plants, the reactive oxygen species (ROS) formed during normal conditions are essential in regulating several processes, like stomatal physiology, pathogen immunity and developmental signaling. However, biotic and abiotic stresses can cause ROS over-accumulation leading to oxidative stress. Therefore, a suitable equilibrium is vital for redox homeostasis in plants, and there have been major advances in this research arena. Salicylic acid (SA) is known as a chief regulator of ROS; however, the underlying mechanisms remain largely unexplored. SA plays an important role in establishing the hypersensitive response (HR) and systemic acquired resistance (SAR). This is underpinned by a robust and complex network of SA with Non-Expressor of Pathogenesis Related protein-1 (NPR1), ROS, calcium ions (Ca2+), nitric oxide (NO) and mitogen-activated protein kinase (MAPK) cascades. In this review, we summarize the recent advances in the regulation of ROS and antioxidant defense system signalling by SA at the physiological and molecular levels. Understanding the molecular mechanisms of how SA controls redox homeostasis would provide a fundamental framework to develop approaches that will improve plant growth and fitness, in order to meet the increasing global demand for food and bioenergy.

Plants face different types of stresses, including biotic and abiotic stresses. Among various abiotic stress, low-temperature stress alters various morphological, cytological, physiological, and other biochemical processes in plants. To thrive in such condition’s plants must adopt some strategy. Out of various strategies, the approach of using plant growth regulators (PGRs) gained a prominent role in the alleviation of multiple stresses. Salicylic acid, application triggers tolerance to both biotic and abiotic stresses via regulation of various morpho-physiological, cytological, and biochemical attributes. SA is shown to alleviate and regulate the various cold-induced changes. Both endogenous and exogenously applied SA show an imperative role in the alleviation of cold-induced changes by activating multiple signaling pathways like ABA-dependent or independent pathway, Ca2+ signaling pathway, mitogen-activated protein kinase (MAPKs) pathway, reactive oxygen species (ROS), and reactive nitrogen species (RNS) pathways. Activation of these pathways leads to the amelioration of the cold-induced changes by increasing production of antioxidants, osmolytes, HSPs and other cold-responsive proteins like LEA, dehydrins, AFPs, PR proteins, and various other proteins. This review describes the tolerance of cold stress by SA in plants through the involvement of different stress signaling pathways.

Menthol mint (Mentha arvensis L.) cultivation is significantly affected by the heavy metals like cadmium (Cd) which also imposes severe health hazards. Two menthol mint cultivars namely Kosi and Kushal were evaluated under Cd stress conditions. Impact of plant growth regulators (PGRs) like salicylic acid (SA), gibberellic acid (GA(3)) and triacontanol (Tria) on Cd stress tolerance was assessed. Reduced growth, photosynthetic parameters, mineral nutrient concentration, and increased oxidative stress biomarkers like electrolyte leakage, malondialdehyde, and hydrogen peroxide contents were observed under Cd stress. Differential upregulation of proline content and antioxidant activities under Cd stress was observed in both the cultivars. Interestingly, low electrolyte leakage, lipid peroxidation, hydrogen peroxide and Cd concentration in leaves were observed in Kushal compared to Kosi. Among all the PGRs tested, SA proved to be the best in improving Cd-stress tolerance in both the cultivars but Kushal responded better than Kosi.

The aim of current investigation was to perform proteomics and physio-chemical studies to dissect the changes in contrasting varieties (S-22 and PKM-1) of Lycopersicon esculentum under low-temperature stress. Plant grown under variable low-temperature stress were analysed for their growth biomarkers, antioxidant enzyme activities, and other physiological parameters, which headed toward the determination of protein species responding to low-temperature and 24-epibrassinolide (EBL) concentrations. The plants grown under temperatures, 20/14, 12/7, and 10/3 °C recorded significantly lower growth biomarkers, SPAD chlorophyll, net photosynthetic rate and carbonic anhydrase activity in S-22 and PKM-1. Moreover, the combined effect of EBL and hydrogen peroxide (H2O2) significantly improved the parameters mentioned above and consecutively upgraded the different antioxidant enzymes (CAT and SOD) with higher accumulation of proline under stress and stress-free environments. Furthermore, proteomics study revealed that the maximum number of differentially expressed proteins were detected in S-22 (EBL + H2O2); while treatment with EBL + H2O2 + low temperature lost expression of 20 proteins. Overall, three proteins (O80577, Q9FJQ8, and Q9SKL2) took a substantial part in the biosynthesis of citrate cycle pathway and enhanced the growth and photosynthetic efficiency of tomato plants under low-temperature stress.

Nickel (Ni) is a fundamental component that assumes a vital role in managing plant growth and development. Its acquisition in soil is presently viewed as a consequential ecological issue imperilling crop productivity globally. Brassinosteroid and low concentration of H2O2 as signalling molecule could modify stomatal movement, root morphology, photosynthetic effectiveness and generation of antioxidants and finally growth traits to make the tomato plants more tolerant to Ni stress. Therefore, a study was conducted to study the effect of exogenously applied epibrassinolide (EBL; foliar spray) and H2O2 (root dipping) to nickel (Ni) stressed plants. EBL and H2O2 applied through different modes modified stomatal movement, root morphology, photosynthetic effectiveness and growth traits of Solanum lycopersicum L. plants grown under stress free and surplus Ni. The increased Ni- tolerance of tomato plants caused by EBL and H2O2 could be attributed to its capability to restrict Ni uptake, reduce Ni- inflicted oxidative burst as illustrated by lower levels of hydrogen peroxide, superoxide and electrolyte leakage in Ni- stressed plants. In addition, EBL and H2O2 increased the antioxidant capability in Ni stressed plants by sustaining increased activities of enzymes for ROS-detoxification, particularly catalase (CAT), guaiacol peroxidase (GPOX) and superoxide dismutase (SOD) and proline accumulation. These improved activities of antioxidant enzymes and accumulation of proline (osmolyte) elicited by the blend of EBL and H2O2, would have retained the ability to confer resilience to Solanum lycopersicum plants exposed to higher doses of Ni. This study further affirms that the combined application of EBL and H2O2 in various ways proved very effective to ameliorate the effects of Ni toxicity in tomato plants through modification of stomatal movement, root morphology, photosynthetic effectiveness and growth traits.

Brassinosteroids and polyamines are generally used to surpass different abiotic stresses like heavy metal toxicity in plants. The current study was conducted with an aim that 24-epibrassinolide (EBL) and/or spermidine (Spd) could modify root morphology, movement of stomata, cell viability, photosynthetic effectiveness, carbonic anhydrase and antioxidant enzyme activities in Brassica juncea under manganese (Mn) stress (30 or 150 mg kg−1 soil). EBL (10−8 M) and/or Spd, (1.0 mM) were applied to the foliage of B. juncea plants at 35 days after sowing (DAS), grown in the presence of Mn (30 or 150 mg kg−1 soil). High Mn concentration (150 mg kg−1 soil) altered root morphology, affected stomatal movement, reduced the viability of cells and photosynthetic effectiveness and increased the production of reactive oxygen species (O 2 ·− and H2O2) in the leaves and antioxidant defense system of B. juncea at 45 DAS. Furthermore, exogenous treatment of EBL and Spd under stress and stress- free conditions improved the aforesaid traits while decreased the O 2 ·− and H2O2 production. Therefore, EBL and Spd could be applied to the foliage of B. juncea plants for the better growth under metal stress.

Selenium (Se) is a well-known beneficial element in plants. The window of Se between toxic and optimal concentration is narrow and uneven which fluctuates with plants species. This experiment was aimed to investigate the morpho-physiological, microscopic and histochemical responses of two different varieties of tomato (S-22 and PKM-1), exposed to different concentrations of Se (0, 10, 40 or 80 µM), applied to soil at 30 days after transplantation (DAT). At 40 DAT, it was observed that high concentrations (40 or 80 µM) of Se radically increased oxidative stress examined by elevated reactive oxygen species (ROS), malondialdehyde (MDA) content, cell death, electrolyte leakage and decreased chlorophyll content leading phenotypic symptoms of Se-induced toxicity like stunted growth and chlorosis. Furthermore, high doses of Se altered the chloroplast and stomatal organisation, and adversely affected the photosynthetic performance of plants. But low concentration of Se improved the plant dry mass, photosynthesis, Rubisco activity, protein content and maintained the steady-state equilibrium among ROS generation and antioxidant enzymes like catalase, peroxidase and superoxide dismutase. Our outcomes proposed that high concentration of Se generated toxicity (phyto-selenosis), whereas lower concentration of Se-triggered positive impact by improving growth, photosynthetic traits and maintaining steady-state equilibrium between scavenging-system and ROS generation.

Brassinosteroids and hydrogen peroxide (H2O2) are extensively used to combat several environmental factors, including heavy metal stress in plants, but their cumulative impact on the maintenance of copper (Cu) homeostasis in plants could not be dissected at elevated level. This study was executed to explore the roles of 24-epibrassinolide (EBL; foliar) and H2O2 (root dipping) in resilience of tomato (Solanum lycopersicum L.) plants to Cu stress. The cumulative effect of EBL and H2O2 in tomato plants grown under Cu stress (10 or 100 mg kg−1 soil) were assessed. Roots of 20 d old plants were submerged in 0.1 mM of H2O2 solution for 4 h and subsequently transplanted in the soil-filled earthen pots and at 30 day after transplantation (DAT), the plants were sprinkled with deionized water (control), and/or 10−8 M EBL and plant performances were evaluated at 40 DAT. High Cu (100 mg kg−1 soil) concentration considerably reduced photosynthetic efficacy, cell viability, and plant growth, and deformed chloroplast ultrastructure and root morphology with altered stomatal behavior, but boosted the activity of antioxidant enzymes, proline content and electrolyte leakage in the leaves of tomato. Moreover, EBL and H2O2 implemented through distinct modes improved photosynthetic efficiency, modified chloroplast ultrastructure, stomatal behavior, root structure, cell viability and production of antioxidants and proline (osmolyte) that augmented resilience of tomato plants to Cu stress. This study revealed the potential of EBL and H2O2 applied through distinct mode could serve as an effective strategy to reduce Cu-toxicity in tomato crop.

Utilization of nanoparticles (NPs) has increased tremendously in recent years by virtue of their unique properties, which can be applied for numerous purposes. Titanium (Ti)/titanium dioxide (TiO2) NPs are among the most widely used NPs for applications including the agriculture sector. Titanium is considered a beneficial element for plant growth and its nano form can be used to improve growth and yield of plants. Research has shown that TiO2 NPs generate both positive as well as a negative impact to plant growth. This review discusses current knowledge of TiO2 NPs including their interactions, transport, and translocation within plants, and future perspectives regarding their use.

In plants, hydrogen peroxide (H2O2) acts as a signalling molecule that facilitates various biochemical and physiological processes. H2O2 is a versatile molecule, involved in several cellular processes both under stress and stress-free conditions. In regulating plant metabolism under stress conditions, exogenous application of H2O2 also plays a pivotal role which is manifested in improved growth, photosynthetic capacity, and antioxidant protection. Abiotic stress is an inevitable environmental factor that extensively affects and reduces growth, quality, yield, and productivity of plants. Several signalling pathways involved in H2O2-mediated stress and defense responses have been extensively studied and there is ample scope of additional research that could further clarify the mechanism and modulating factors which regulate these pathways. An attempt has been made to dissect the role of H2O2 under low temperature stress and how it affects plant growth and development, photosynthetic capacity, regulation of antioxidant system, and signalling.

Salicylic acid (SA) and polyamines (PA) are widely used to overcome various abiotic stresses including salt (NaCl) stress in plants. In the present investigation, co-application efficacies of SA and PA on the salt stress (200 mM NaCl) were evaluated in Lycopersicon esculentum. After transplantation, at 10-d stage, seedlings were exposed to NaCl through soil and then allowed to grow till 30-d stage. At 31-d stage of growth, plants were sprayed with double distilled water (control) or spermidine (1.0 mM) and/or SA (10–5 M). The salt stress significantly reduced the growth, gas-exchange parameters, but increased antioxidant enzymes and proline content in the leaves. Moreover, the loss caused by salt stress was successfully restored by the following treatment of spermidine and SA.

This study was conducted to unravel the EBL mediated changes on the enzymes of proline metabolism under combined stress of aluminum and salt through varied mode of application. The results of the study revealed that application of EBL through different mode significantly increased the activities of P5CS and δ-OAT, proline content, photosynthetic efficiency and various enzymes of antioxidant system whereas, these parameters were further accelerated in the plants exposed to combined stress of aluminum and salt followed by EBL treatment. These findings indicate that exogenous application of EBL modified the activity of enzymes of proline metabolism and also scavenges the excess reactive oxygen species through improved activities of antioxidant enzymes which could have provided the ability to confer tolerance in wheat plants under combination of aluminum and salt stress.

Melatonin (MEL) is the potential biostimulator molecule, governing multiple range of growth and developmental processes in plants, particularly under different environmental constrains. Mainly, its role is considered as an antioxidant molecule that copes with oxidative stress through scavenging of reactive oxygen species and modulation of stress related genes. It also enhances the antioxidant enzyme activities and thus helps in regulating the redox hemostasis in plants. Apart from its broad range of antioxidant functions, it is involved in the regulation of various physiological processes such as germination, lateral root growth and senescence in plants. Moreover this multifunctional molecule takes much interest due to its recent identification and characterization of receptorCandidate G-protein-Coupled Receptor 2/Phytomelatonin receptor(CAND2/PMTR1) in Arabidopsis thaliana. In this compiled work, different aspects of melatonin in plants such as melatonin biosynthesis and detection in plants, signaling pathway, modulation of stress related genes and physiological role of melatonin under different environmental stresses have been dissected in detail.

Polyamines (PAs) are recognized as plant growth regulators that are involved in the stress management in various crops. In the current study, mitigative roles of spermidine (Spd) and putrescine (Put) were assessed in manganese (Mn) stressed Brassica juncea plants. Spd or Put (1.0 mM) were applied to the foliage of Brassica juncea at 35 days after sowing (DAS) grown in the presence of Mn (30 or 150 mg kg−1 soil). The higher level of Mn (150 mg kg−1) diminished photosynthetic attributes and growth, enhanced the production of reactive oxygen species (ROS) like hydrogen peroxide (H2O2) and superoxide anion ( O 2 · − ) content, affected stomatal movement and increased the Mn concentration in roots and shoots of the plant at 45 DAS, whereas it enhanced the activities of various antioxidant enzymes and proline content in the foliage of Brassica juncea plants. On the other hand, treatment of PAs (Spd or Put) to Mn stressed as well as non-stressed plants resulted in a remarkable improvement in the stomatal behaviour, photosynthetic attributes, growth and biochemical traits, decreased the production of ROS (H2O2 and O 2 · − ) and concentration of Mn in different parts of plant. It is concluded that out of the two polyamines (Spd or Put), Spd proved more efficient and enhanced growth, photosynthesis, and metabolic state of the plants which bestowed tolerance and helped the plants to cope efficiently under Mn stress.

Of all the non-essential heavy metals, cadmium (Cd) is perhaps the metal which has attracted the most attention in soil science and plant nutrition due to its potential toxicity to humans, and also its relative mobility in the soil-plant system. This review summarizes the toxic symptoms of Cd in plants (i.e. growth retardation, alterations of photosynthesis, stomatal movement, enzymatic activities, water relations, interferences with mineral uptake, protein metabolism, membrane functioning, etc.) but also includes the mechanisms of cadmium uptake, translocation and deposition. Moreover, it also throws light on chelation, including identification of Cd ligands present in cytosol and vascular tissue. Cadmium-induced oxidative stress is also considered as one of the most widely studied topics in this review.

Brassinosteroids (BRs) is a naturally occurring phytohormone of steroidal nature, which take part in the regulation of growth and development of plants through their life cycle. In the present era, availability of a larger number of biotic and abiotic factors restrict the gross production of principal crops. Handful of literature revealed that BRs play vital role in modulating the plant response to various abiotic stresses through alteration in the activities of antioxidant enzymes and proline metabolism by inducing expression of genes involved in defense and antioxidant responses in plants. This plant steroid also found to be very successful in mitigating the damage caused by the oxidative stress under varied unfavorable environmental conditions. These days most debatable part in the BRs research field is the molecular mechanisms associated with the enhanced activities of antioxidant enzymes and proline accumulation in plants under various developmental and environmental cues. Here, we will shed lights on the action mechanisms by which BRs enhanced the activities of antioxidant enzymes and proline accumulation under both stress and stress-free conditions and cross talk with other plant hormones. Therefore, understanding the physiological, biochemical and molecular aspects of BRs would help in developing abiotic stress tolerance in plants in a more significant manner.

With the advent of sophisticated technology and techniques in farming sectors, the problem of salt stress has increased manifold. Salt stress causes various alterations ranging from genetic to morphological level in crop plants. In order to improve salt stress tolerance, some sustainable strategies should be chalked out which on one hand engineer tolerance to salt stress and on the other side enhance photosynthesis, growth, and yield of crop plants. Plants have developed numerous strategies of tolerance to overcome the menace of salt stress. Among various practices adopted, the signalling crosstalk of plant growth regulators (PGRs) has received special attention recently among plant physiologists. In the present chapter, an appraisal has been prepared to explore the tolerance trade-off mediated by PGRs, viz. salicylic acid (SA), nitric oxide (NO), brassinosteroids (BRs), abscisic acid (ABA), methyl jasmonate (MeJ), and melatonin (Mel), in plants under salt-challenged environments. The present chapter highlights the role of PGRs for engineering tolerance against salt stress in various crop plants. Furthermore, the underlying mechanisms by which plants perceive signals of stress, which trigger signal transduction cascades, have also been elaborated. Moreover, the role of tolerance trade-off under salinity stress by PGRs, namely, SA, NO, BRs, ABA, MeJ, and Mel, has also been dissected in detail.

The present investigation was conducted to evaluate the silicon (Si) mediated responses in different cultivars of Indian mustard (Brassica juncea) and to evaluate if Si could be used as an essential, beneficial, or quasi-essential element for growth and development of these cultivars. Surface sterilized seeds were sown in pots and allowed to germinate under natural environmental conditions. At 10, 12, 14, 16, and 18 days after germination, a range of Si concentrations (0.0, 0.2, 0.4, 0.8 and 1.6 mM) was administered to the soil and at 30 days post germination the plants were sampled to assess growth and development, leaf gas exchange traits and plant biochemical parameters, including activities of carbonic anhydrase, catalase, peroxidase, superoxide dismutase, and protein and proline content. The results demonstrate a dual response to Si concentration: 0.8 mM of Si significantly increased plant growth and development (length of root and shoot, fresh and dry biomass, and leaf area) and photosynthetic efficiency, and enhanced the antioxidant response in T-59 over all the other cultivars tested, whereas, 1.6 mM of Si significantly reduced the above parameters. It is therefore concluded that low levels of Si could be used as a quasi-essential element for enhanced photosynthetic efficiency and antioxidant response ofBrassica junceaplants; however, the response is cultivar specific and concentration dependent.

Hydrogen peroxide (H2O2) acts as a significant regulatory component interrelated with signal transduction in plants. The positive role of H2O2 in plants subjected to myriad of abiotic factors has led us to comprehend that it is not only a free radical, generated as a product of oxidative stress, but also helpful in the maintenance of cellular homeostasis in crop plants. Studies over the last two centuries has indicated that H2O2 is a key molecule which regulate photosynthesis, stomatal movement, pollen growth, fruit and flower development and leaf senescence. Exogenously-sourced H2O2 at nanomolar levels functions as a signalling molecule, facilitates seed germination, chlorophyll content, stomatal opening, and delays senescence, while at elevated levels, it triggers oxidative burst to organic molecules, which could lead to cell death. Furthermore, H2O2 is also known to interplay synergistically or antagonistically with other plant growth regulators such as auxins, gibberellins, cytokinins, abscisic acid, jasmonic acid, ethylene and salicylic acid, nitric oxide and Ca2+ (as signalling molecules), and brassinosteroids (steroidal PGRs) under myriad of environmental stresses and thus, mediate plant growth and development and reactions to abiotic factors. The purpose of this review is to specify accessible knowledge on the role and dynamic mechanisms of H2O2 in mediating growth responses and plant resilience to HM stresses, and its crosstalk with other significant PGRs in controlling various processes. More recently, signal transduction by mitogen activated protein kinases and other transcription factors which attenuate HM stresses in plants have also been dissected.

Plant growth and development could be modulated by minute concentrations of hydrogen peroxide (H2O2) which serves as a signaling molecule for various processes. The present work was conducted with an aim that H2O2 could also modify root morphology, morphology and movement of stomata, photosynthetic responses, activity of carbonic anhydrase, and antioxidant systems in tomato (Solanum lycopersicum L.) plants under copper stress (Cu; 10 or 100 mg kg-1 soil). Roots of 20 d old plants were dipped in 0.1 or 0.5 mM of H2O2 solution for 4 h and then transplanted to the soil filled in earthen pots. High Cu stress (100 mg kg-1 soil) altered root morphology, reduced chlorophyll content and photosynthetic capacity and also affected movement of stomata and generation of antioxidant species at 40 d after transplantation. Further, root dipping treatment of H2O2 to plants under stress and stress-free conditions enhanced accumulation of proline and activity of catalase, peroxidase, and superoxide dismutase, whereas production of superoxide radical (O2•¯) and H2O2 were decreased. Overall, H2O2 treatment improved growth, photosynthesis, metabolic state of the plants which provided tolerance and helped the plants to cope well under Cu stress.

High temperature poses a severe extortion to productivity of many crops like wheat. Therefore, well documented roles of brassinosteroid (BR) and silicon (Si) in terms of abiotic stress tolerance, the current study was designed to evaluate the response of wheat (Triticum aestivum L. Var. PBW-343) to 24-epibrassinolide (EBL) mediated by silicon grown under high temperature stress. At 10- and 12-day stage after sowing, the seedlings were administered Si (0.8 mM) through the sand, and the plants at 20, 22, or 24 days after sowing (DAS) were given EBL (0.01μM) through foliage. Plants were treated to high-temperature stress (35/28 or 40/35 °C), for 24 h with 12-h photoperiod in plant growth chamber at 25- and 26-day stage of growth. High temperatures cause significant reduction in growth performance and photosynthesis-related attributes at 35 days after sowing. However, antioxidant enzymes and proline content also augmented substantially with increasing temperature. BR and Si enhanced antioxidant activity and proline content, which was earlier increased by the high temperature. It is established that interaction of EBL and Si considerably improved the growth features, photosynthetic efficacy, and several biochemical traits under high-temperature stress through elevated antioxidant system and osmoprotectant.

In the past decade, characterization of the host targets of pathogen virulence factors took a center stage in the study of pathogenesis and disease susceptibility in plants and humans. However, the impressive knowledge of host targets has not been broadly exploited to inhibit pathogen infection. Here, we show that host target modification could be a promising new approach to "protect" the disease-vulnerable components of plants. In particular, recent studies have identified the plant hormone jasmonate (JA) receptor as one of the common targets of virulence factors from highly evolved biotrophic/hemibiotrophic pathogens. Strains of the bacterial pathogen Pseudomonas syringae, for example, produce proteinaceous effectors, as well as a JA-mimicking toxin, coronatine (COR), to activate JA signaling as a mechanism to promote disease susceptibility. Guided by the crystal structure of the JA receptor and evolutionary clues, we succeeded in modifying the JA receptor to allow for sufficient endogenous JA signaling but greatly reduced sensitivity to COR. Transgenic Arabidopsis expressing this modified receptor not only are fertile and maintain a high level of insect defense, but also gain the ability to resist COR-producing pathogens Pseudomonas syringae pv. tomato and P. syringae pv. maculicola. Our results provide a proof-of-concept demonstration that host target modification can be a promising new approach to prevent the virulence action of highly evolved pathogens.

This study was conducted to provide an insight into the effect of Se (through soil) induced changes in Brassica juncea plants in the presence and absence of 24-epibrassinolide (EBL; foliar). The Se treatments showed dual response, 10 μM of Se significantly increased growth, water relations, photosynthetic attributes along with carbonic anhydrase activity whereas its higher concentrations proved inhibitory in concentration dependent manner. The follow-up application of EBL to the Se stressed plants improved growth, water relations, photosynthesis and simultaneously enhanced the various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase with the excess accumulation of proline. In addition to this, 10 μM Se increases the efficacy of 10(-8) M of EBL and both in combination showed maximum increase for the growth and photosynthetic traits of plants. On the other hand, the elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the Se-stressed plants resulting in improved growth, water relations and photosynthesis.

Hydrogen peroxide (H2O2) in minute concentrations serves as a signaling molecule for processes involved in the growth and development of plants. The present study aimed to explore the role of seed treatment with H2O2 on growth biomarkers, photosynthetic traits, activities of carbonic anhydrase, and various antioxidant enzymes in 45-day-old plants of mung bean (Vigna radiata L. Wilczek) cv. SML-668 under non-stress conditions. The seeds were soaked in 0, 0.01, 0.1, or 0.5 mM H2O2 for 2, 4, or 8 h, and then inoculated with Rhizobium, sown in sandy loam soil, and allowed to grow for 45 days. The plants that developed from the H2O2-treated seeds demonstrated improved growth and photosynthetic attributes, enhanced activity of various antioxidant enzymes (e.g., catalase, peroxidase, and superoxide dismutase), and higher accumulation of proline than plants from non-treated seeds. The H2O2-triggered upregulation of antioxidant enzymes and proline (osmolyte) could have resulted in the observed improvement of growt...

Brassinosteroids (BRs) have been implicated to overcome various abiotic stresses, and low temperature stress poses a serious threat to productivity of various horticultural crops like tomato. Therefore, a study was conducted to unravel the possible role of BRs in conferring alleviation to low temperature stress in Lycopersicon esculentum. Twenty-day-old seedlings of tomato var. S-22 (chilling tolerant) and PKM-1 (chilling sensitive) were sown in earthen pots, and at 40 days stage of growth, plants were exposed to varied levels of low temperatures (10/3, 12/7, 20/14, or 25/18 °C) for 24 h in a growth chamber. At 50 days stage of growth, the foliage of plants were sprayed with 0 or 10(-8) M of BRs (28-homobrassinolide or 24-epibrassinolide), and 60-day-old plants were harvested to assess various physiological and biochemical parameters. Low temperatures induced a significant reduction in growth traits, chlorophyll content, and rate of photosynthesis in both the varieties differentially. Activities of antioxidant enzymes (catalase, peroxidase, and superoxide dismutase) and leaf proline content also increased substantially in both the varieties with decreasing temperature. On the other hand, treatment of BRs under stress and stress-free conditions significantly increased the aforesaid growth traits and biochemical parameters. Moreover, BRs further accelerated the antioxidative enzymes and proline content, which were already enhanced by the low temperature stress. Out of the two analogues of BRs tested, 24-epibrassinolide (EBL) was found more effective for both the varieties of tomato. EBL was found more potent stress alleviator against low temperature in both varieties of tomato.

The objective of this study was to establish relationship between manganese-induced toxicity and antioxidant system response in Brassica juncea plants and also to investigate whether brassinosteroids activate antioxidant system to confer tolerance to the plants affected with manganese induced oxidative stress. Brassica juncea plants were administered with 3, 6, or 9 mM manganese at 10-day stage for 3 days. At 31-day stage, the seedlings were sprayed with deionized water (control) or 10(-8) M of 24-epibrassinolide, and plants were harvested at 45-day stage to assess growth, leaf gas-exchange traits, and biochemical parameters. The manganese treatments diminished growth along with photosynthetic attributes and carbonic anhydrase activity in the concentration-dependent manner, whereas it enhanced lipid peroxidation, electrolyte leakage, accumulation of H2O2 as well as proline, and various antioxidant enzymes in the leaves of Brassica juncea which were more pronounced at higher concentrations of manganese. However, the follow-up application of 24-epibrassinolide to the manganese stressed plants improved growth, water relations, and photosynthesis and further enhanced the various antioxidant enzymes viz. catalase, peroxidase, and superoxide dismutase and content of proline. The elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the manganese-stressed plants resulting in improved growth and photosynthetic attributes.

Brassinosteroids (BRs) and polyamines, well-established growth regulators, play a key role in abiotic stress response in plants. In the present study, we examined the role of 24-epibrassinolide (EBL, an active BR) and/or putrescine (Put) in the salt-induced stress in cucumber. The 15-d-old plants were exposed to 100 mM NaCl and they were subsequently treated by exogenous EBL and/or Put. The salt stress reduced significantly plant growth and gas-exchange parameters, and increased proline content and electrolyte leakage in the leaves. Toxic effects induced by salt stress were completely overcome by the combination of EBL and Put. EBL and/or Put treatments improved the growth parameters of the NaCl-treated plants, such as shoot length, root length, fresh and dry mass. Our data also indicated that applications of EBL and Put upregulated the activities of the antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase under salt stress.

Low temperature can delay growth and development, reduce productivity, or cause plant death. An experiment was carried out to determine the most sensitive and most tolerant tomato (Solanum lycopersicum L.; variety S-22, Selection N-5, Pusa Gorav, K-21, Pusa Ruby, Hera Research, and PKM-1) to low temperature. Forty-day-old seedlings were exposed to day/night temperatures of 10/3°C, 12/7°C, 20/14°C, or 25/18°C (control) for 24 h in a plant growth chamber and then transferred to ambient environmental conditions in a net house and maintained for 60 days. Decreasing temperature led to decreases in growth, chlorophyll content, and photosynthesis rate in all varieties. Activity of antioxidant enzymes catalase, peroxidase, and superoxide dismutase and proline accumulation in leaves increased in all varieties as temperature decreased. Variety S-22 had the most antioxidant enzyme activity and proline accumulation and ‘PKM-1’ had the lowest antioxidant enzyme activity and proline content; these were classified as to...

Hydrogen peroxide (H2O2) in minute quantity serves as a signalling molecule. However, the role of H2O2 in combination with brassinosteroids (stress regulators) in plants under toxic levels of copper, is poorly understood. With an aim to explore and elaborate their role in plants subjected to abiotic stress, the surface sterilized seeds of mung bean (Vigna radiata) were sown in earthen pots filled with soil and manure enriched with different levels of Cu2+ (50 or 100 mg kg−1 of soil) and allowed to grow under natural environmental conditions. At 15 and 20 days stage, the plants were sprayed with H2O2 (2.5 mM) and/or 28-homobrassinolide (HBL, 10−5 mM), respectively. At 45 days stage, the analysis of the plants revealed that the presence of copper in the soil caused a significant decrease in growth characteristics, activity of carbonic anhydrase and nitrate reductase, relative water content, chlorophyll content and the rate of photosynthesis whereas, the activity of antioxidant enzymes (catalase, peroxidase and superoxide dismutase) and the proline accumulation in leaves increased in Cu stressed plants. However, the exogenously applied HBL and/or H2O2, in the absence of Cu-stress strongly favoured the growth, photosynthetic parameters and also improved the activity of antioxidant enzymes and the proline content. Furthermore, the combined application of HBL and H2O2 to the foliage of the stressed plants neutralized the toxic impact of all copper regimes. Therefore, we are of the opinion that these chemicals somehow maintained the homeostasis of the metal in the plants that exhibit healthy growth.

Brassinosteroids (BRs) are polyhydroxylated steroidal plant hormones that play pivotal role in the regulation of various plant growth and development processes. BR biosynthetic or signaling mutants clearly indicate that these plant steroids are essential for regulating a variety of physiological processes including cellular expansion and proliferation, vascular differentiation, male fertility, timing senescence, and leaf development. Moreover, BRs regulate the expression of hundreds of genes, affect the activity of numerous metabolic pathways, and help to control overall developmental programs leading to morphogenesis. On the other hand, the potential application of BRs in agriculture to improve growth and yield under various stress conditions including drought, salinity, extreme temperatures, and heavy metal (Cd, Cu, Al, and Ni) toxicity, is of immense significance as these stresses severely hamper the normal metabolism of plants. Keeping in mind the multifaceted role of BRs, an attempt has been made to cover the various aspects mediated by BRs particularly under stress conditions and a possible mechanism of action of BRs has also been suggested.

Salt stress is among the major abiotic stresses that adversely affect the global crop production and its adverse impacts are getting more serious in the regions where saline water is used for irrigation. It induces reactive oxygen species, alters the activity of antioxidant system and adversely affects the process of photosynthesis. Various strategies have been employed to mitigate the deleterious effects of salt stress. Presently, the recommended strategies to overcome the adverse effects of salt stress include the use of tolerant cultivars, ameliorative water management and diverse cultural practices. However, none of these approaches have been found to be fully effective under salt stress conditions. An alternative and technically simpler approach to induce salt stress tolerance is the exogenous application of plant growth regulators (PGRs). This technique has gained significant importance during the past decade. PGRs have been implicated to regulate a wide range of metabolic and physiological activities in plants, ranging from cell division and organogenesis to protection against biotic and abiotic stresses. One of the important factors for enhanced plant productivity by PGRs is their efficiency to overcome the salt-induced stress conditions. Recent findings on the effects of brassinosteroids and polyamines on the salt stress tolerance of crops open new avenues to address the salinity problems. This review enlightens the role of brassinosteroids and polyamines in different plant processes like their role in regulation of photosynthesis, antioxidant systems and other related aspects, thereby improving overall performance of plants.

Polyamines (PAs) are aliphatic polycations that are widespread in living organisms. In this review, we are focusing the correlation between endogenous PA titers and physiological perturbations and on the protective role of various analogues of PAs against abiotic stresses. PAs are involved in many physiological processes, such as cell growth and development and also respond to diverse abiotic stresses. Polyamines level shifts in different ways depending on several factors, such as plant species, tolerance or sensitivity to stress, and duration of stress. Exogenously supplied PAs protected plants from abiotic stress, whereas transgenic plants overexpressing PA biosynthetic genes exhibited stress tolerance. On the other hand, loss-of-function mutant of PA biosynthetic genes, or decrease of PA titers, resulted to decrease stress tolerance.

Brassinosteroids (BRs) are known to be naturally occurring polyhydroxylated plant steroids that showed diverse roles in regulation of various physiological and developmental processes in plants under both natural and stressful conditions. With the advancement of various omic approaches, informations available provide huge data to understand the processes responsible for BRs biosynthesis, transport, signalling, and metabolism pathways. Moreover, in the recent past BRs have shown the ability to cross talk with other phytohormones such as auxin, polyamines, cytokinin, ethylene, and jasmonic acid in regulating varied ranges of physiological and biochemical processes in plants. On the other hand, the exogenous application of BRs in agriculture to improve growth and yield under various stress conditions including drought, salinity, extreme temperatures, and heavy metal toxicity is of immense significance as these stresses severely hamper the normal metabolism of plants. The information available till date regarding BRs will definitely help in establishing various mechanisms which modulate various processes in plants and overcome the future challenges in agriculture.

This study was designed to assess the combined effect of both aluminium and salt stress on the processes and molecules pertinent to these stresses and to establish relationship between these two stresses on the basis of photosynthetic attributes and antioxidant enzymes in wheat cultivars. Seven different varieties of wheat grown under environmentally controlled conditions. At 10 days stage of growth, plants were treated with NaCl (100 or 150 mM) and/or Al (05 or 10 mM) through soil. At 30 days stage, treatment of Al and salt stress alone showed the similar deteriorating response in terms of photosynthetic traits and LWP whereas, electrolyte leakage, lipid peroxidation, H2O2 content along with enzymes of antioxidant and proline content varied in different varieties of wheat. Moreover, the combination of Al and salt stress further increased the antioxidant enzymes and proline accumulation. However, salt stress restrict the uptake of Al by roots in significant manner under combine treatment of Al and salt stress. The pattern of tolerance was observed on the basis of enhanced antioxidant system and proline accumulation and cultivar LOK-1 and 502 showed maximum and minimum tolerance respectively against the combination of salt and aluminium stress.

The objective of this study was to explore the response of 24-epibrassinolide to improve the biological yield of Ni-tolerant and Ni-sensitive varieties of Vigna radiata and also to test the propositions that 24-epibrassinolide induced up-regulation of antioxidant system protects the efficiency of V. radiata, grown under Ni-stress. Surface sterilized seeds of var. T-44 (Ni-tolerant) and PDM-139 (Ni-sensitive) were soaked in DDW (control), 10(-10), 10(-8), or 10(-6) M of 24-epibrassinolide for 8 h (shotgun approach). These treated seeds were then inoculated with specific Rhizobium grown in sandy loam soil supplemented with different levels of Ni 0, 50, 100, or 150 mg Ni kg(-1) of soil and were allowed to grow for 45-days. At this stage of growth, plants were sampled to assess the various growths and nodule related traits as well as selected biochemical characteristics. The remaining plants were allowed to grow to maturity to study the yield characteristics. The results indicated that plant-fresh and dry mass, number of nodules, their fresh and dry mass, leghemoglobin content, nitrogen and carbohydrate content in the nodules, leaf chlorophyll content, activities of nitrate reductase and carbonic anhydrase decreased proportionately with the increasing concentrations of soil nickel. However, the application of 24-epibrassinolide as shotgun approach (pre-sowing seed soaking) to the nickel-stressed or non-stressed plants improved growth, nodulation and enhanced the activity of various antioxidant enzymes (viz. catalase, peroxidase and superoxide dismutase) and also the content of proline. The up-regulation of antioxidant enzymes as well as proline (osmolyte) triggered by 24-epibrassinolide could have conferred tolerance to the Ni-stressed plants resulting in improved growth, nodulation and yield attributes.

This study was hypothesized that salicylic acid elevates the level of antioxidant system that will protect plants from the stress generated by nickel and/or salinity.Seeds of Brassica juncea were sown in sand amended with NiCl(2) (100 mg kg(-1)) and/or 15-day-old seedlings supplied for 3 days with NaCl (150 mM) and were then, at 20-day stage, sprayed with salicylic acid (10(-5) M) to assess selected morphological, physiological, and biochemical parameters at 30-day stage.The combination of Ni and NaCl proved most deleterious and exhibited significant decline in growth, leaf water potential, the level of pigments, and photosynthetic attributes. However, the follow-up treatment with salicylic acid detoxified the stress-generated damages caused by the combination (NiCl(2) and NaCl) and also significantly improved values for the above parameters. The NiCl(2) and/or NaCl increased electrolyte leakage, lipid peroxidation, and H(2)O(2) content but decreased the membrane stability index and activity of nitrate reductase and carbonic anhydrase. However, the salicylic acid treatment in the presence or absence of the stress improved the activity of nitrate reductase and carbonic anhydrase. The activity of antioxidative enzymes and the level of proline exhibited a significant increase in response to NiCl(2) and/or NaCl stress and which enhanced further with the spray of salicylic acid.It is concluded that the elevated level of antioxidative enzymes and level of proline might be responsible for minimizing the Ni and/or salinity-induced toxicity in Indian mustard which is manifested in terms of improved growth and photosynthesis.