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Given their sessile nature, plants continuously face unfavorable conditions throughout their life cycle, including water scarcity, extreme temperatures and soil pollution. Among all, metal(loid)s are one of the main classes of contaminants worldwide, posing a serious threat to plant growth and development. When in excess, metals which include both essential and non-essential elements, quickly become phytotoxic, inducing the occurrence of oxidative stress. In this way, in order to ensure food production and safety, attempts to enhance plant tolerance to metal(loid)s are urgently needed. Nitric oxide (NO) is recognized as a signaling molecule, highly involved in multiple physiological events, like the response of plants to abiotic stress. Thus, substantial efforts have been made to assess NO potential in alleviating metal-induced oxidative stress in plants. In this review, an updated overview of NO-mediated protection against metal toxicity is provided. After carefully reviewing NO biosynthetic pathways, focus was given to the interaction between NO and the redox homeostasis followed by photosynthetic performance of plants under metal excess., (© 2019 Scandinavian Plant Physiology Society.)

We studied the response of ethylene-sensitive (Pusa Jai Kisan) and ethylene-insensitive (SS2) mustard (Brassica juncea) cultivars to 0, 0.5, 1.0 and 2.0 mM SO₄(2-), and the effect of 1.0 mM SO₄(2-) was studied in the amelioration of 50 µM cadmium (Cd). The Cd-induced oxidative stress and Cd accumulation were greater in SS2 than Pusa Jai Kisan, but sulfur (S) application alleviated Cd-induced oxidative stress more prominently in Pusa Jai Kisan by increasing S-metabolism and synthesis of reduced glutathione (GSH) and ethylene production; and promoted photosynthesis and plant dry mass under Cd stress. The ethylene-sensitive cultivar responded more to S treatment under Cd stress and showed increased activity of antioxidant system resulting in increased photosynthesis and growth. Cadmium treatment resulted in rapid increase in ethylene formation which adversely influenced photosynthesis and plant dry mass. However, S and ethephon application to Cd-treated plants lowered ethylene formation to optimal range responsible for maximal GSH synthesis and protection against Cd-induced oxidative stress. The similarity of the effectiveness of 1.0 mM SO₄(2-) with 200 µL L(-1) ethylene source as ethephon in alleviation of 50 µM Cd further verifies that differential alleviation of Cd toxicity in the two cultivars by S was dependent on ethylene production. The results suggest that ethylene production determines Cd stress alleviation by S via regulatory interaction with antioxidant metabolism. Thus, ethylene production and sensitivity bear a prominent role in alleviation of Cd stress by S and can be used as a criterion for developing Cd tolerant genotypes., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Oxidative stress, driven by reactive oxygen, nitrogen, and sulphur species (ROS, RNS, RSS), poses a significant threat to cellular integrity and human health. Generated during mitochondrial respiration, inflammation, UV exposure and pollution, these species damage cells and contribute to pathologies like cardiovascular issues, neurodegeneration, cancer, and metabolic syndromes. Lifestyle factors exert a substantial influence on oxidative stress levels, with mitochondria emerging as pivotal players in ROS generation and cellular equilibrium. Phytochemicals, abundant in plants, such as carotenoids, ascorbic acid, tocopherols and polyphenols, offer diverse antioxidant mechanisms. They scavenge free radicals, chelate metal ions, and modulate cellular signalling pathways to mitigate oxidative damage. Furthermore, plants thriving in high-altitude regions are adapted to extreme conditions, and synthesize secondary metabolites, like flavonoids and phenolic compounds in bulk quantities, which act to form a robust antioxidant defence against oxidative stress, including UV radiation and temperature fluctuations. These plants are promising sources for drug development, offering innovative strategies by which to manage oxidative stress-related ailments and enhance human health. Understanding and harnessing the antioxidant potential of phytochemicals from high-altitude plants represent crucial steps in combating oxidative stress-induced disorders and promoting overall wellbeing. This study offers a comprehensive summary of the production and physio-pathological aspects of lifestyle-induced oxidative stress disorders and explores the potential of phytochemicals as promising antioxidants. Additionally, it presents an appraisal of high-altitude medicinal plants as significant sources of antioxidants, highlighting their potential for drug development and the creation of innovative antioxidant therapeutic approaches. [ABSTRACT FROM AUTHOR]

The effect of chromium (Cr) toxicity on four cultivars of mustard (Brassica juncea), Varuna, Pusa Bold, Rohini and SS2, was studied to select the cultivar with the highest tolerance potential based on higher photosynthesis and growth and lower oxidative stress. Plants receiving Cr showed enhanced superoxide production, accumulation of H2O2 and lipid peroxidation and reductions in photosynthesis and growth. We also studied the potential of ethephon (ethylene source; 2-chloroethyl phosphonic acid) in the amelioration of Cr-induced oxidative stress in the Varuna cultivar which had the highest tolerance potential. Supplementation of plants with ethylene resulted in the alleviation of Cr-induced stress by enhancing proline accumulation and the activity of proline metabolism enzymes and glutamyl kinase, and reduction in proline oxidase activity. Ethylene also increased the activity of enzymes of sulfur assimilation, ATP-sulfurylase and serine acetyl transferase and the content of reduced glutathione (GSH). Furthermore, application of ethylene to plants under Cr stress resulted in ethylene levels in the optimal range and increased the activity of anti-oxidant enzymes such as glutathione reductase and ascorbate peroxidase, reduced oxidative stress and increased photosynthesis and growth. The key role of ethylene in the reversal of Cr-induced photosynthetic inhibition was clearly seen with the application of the ethylene action inhibitor, silver nitrate (AgNO3). The supplementation of AgNO3 resulted in decreased GSH and proline content and lowered ethylene production and photosynthetic and growth compared to ethylene-treated plants. This suggests that ethylene is involved in -reversal of Cr inhibited photosynthesis and growth in mustard. [ABSTRACT FROM AUTHOR]

The increasing trend of addition of heavy metals (HMs) to agricultural lands has increased toxicities in plants leading to significant declines in crop productivity. HM toxicity includes alterations in physiological processes, metabolic activities and overall growth and development of plants. The stimulation of oxidative stress is among the common concerns of toxicity in plants at the cellular level. Plant growth hormones/growth regulators have been key signalling molecules in delivering responses to HMs. The important phytohormones, ethylene and polyamines (PAs), play significant roles in the regulation of various developmental processes and signalling networks in plants. Notably, ethylene and PAs are also involved directly or indirectly in a widespread range of abiotic stress responses and tolerance/adaptation. As ethylene and PA biosynthesis involves a common precursor, S-adenosylmethionine, the interplay between ethylene and PAs is suggested in responses of plants to HM stress. The present work emphasizes the roles of these two phytohormones in signalling and regulation of HMs stress in plants based on the recent available reports. This work (a) overviews biosynthesis and signalling of ethylene and PAs; (b) critically appraises the functions of ethylene and PA, and the role of their promoters in HM-exposed plants; and (c) discusses crosstalk on the major mechanisms potentially governing ethylene and PA for plant HM-tolerance/adaptation. HMs in the appraised herein literature exhibited a differential modulation of PAs and ethylene biosynthetic pathways. In particular, the synergism between the PA and ethylene biosynthesis components could be helpful for plants in improving the ratio of root to shoot, increasing water (nutrients) uptake, modulating major signalling compounds, and thereby maintaining optimum cellular metabolism under HM stress. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a free radical molecule involved in an array of functions under physiological and adverse environmental conditions. As other free radical molecules, NO biological action depends on its cellular concentration, acting as a signal molecule when produced at low concentration or resulting in cellular damage when produced at sufficiently high levels to trigger nitro-oxidative stress. Over the last decade, significant progress has been made in characterizing NO metabolism and action mechanism, revealing that diverse biosynthetic routes can generate this free radical in plants and its action mainly occurs through posttranslational modification (nitration and S-nitrosylation) of target proteins. Intricate crosstalk networks between NO and other signaling molecules have been described involving phytohormones, other second messengers, and key transcription factors. This review will focus on our current understanding of NO interplay with phytohormones and other plant growth regulators under abiotic stress conditions. [ABSTRACT FROM AUTHOR]

Summary We have studied the influence of selenium (Se) and sulfur (S) in the protection of photosynthetic capacity of wheat ( Triticum aestivum ) against cadmium (Cd) stress. The involvement of ethylene and its interaction with proline and antioxidant metabolism in the tolerance of plants to Cd stress was evaluated. Application of Se or S alleviated Cd-induced oxidative stress by increasing proline accumulation as a result of increased activity of glutamyl kinase (GK) and decreased activity of proline oxidase (PROX). These nutrients also induced the activity of ATP-sulfurylase and serine acetyl transferase and the content of cysteine (Cys), a precursor for the synthesis of both reduced glutathione (GSH) and ethylene. Further, application of Se and S to plants under Cd stress reduced ethylene level and increased the activity of glutathione reductase (GR) and glutathione peroxidase (GPX), reduced oxidative stress and improved photosynthesis and growth. The involvement of ethylene in Se and S-mediated alleviation of Cd stress was substantiated with the use of ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The use of AVG reversed the effects of Se and S on ethylene, content of proline and GSH and photosynthesis. The results suggested that Se and S both reversed Cd-induced oxidative stress by regulating ethylene formation, proline and GSH metabolism. Thus, Se or S-induced regulatory interaction between ethylene and proline and GSH metabolism may be used for the reversal of Cd-induced oxidative stress. [ABSTRACT FROM AUTHOR]

The role of gibberellic acid (GA) or sulfur (S) in stimulation of photosynthesis is known. However, information on the involvement of ethylene in GA-induced photosynthetic responses and cadmium (Cd) tolerance is lacking. This work shows that ethylene is involved in S-assimilation, photosynthetic responses and alleviation of Cd stress by GA in mustard ( Brassica juncea L.). Plants grown with 200 mg Cd kg −1 soil were less responsive to ethylene despite high ethylene evolution and showed photosynthetic inhibition. Plants receiving 10 μM GA spraying plus 100 mg S kg −1 soil supplementation exhibited increased S-assimilation and photosynthetic responses under Cd stress. Application of GA plus S decreased oxidative stress of plants grown with Cd and limited stress ethylene formation to the range suitable for promoting sulfur use efficiency (SUE), glutathione (GSH) production and photosynthesis. The role of ethylene in GA-induced S-assimilation and reversal of photosynthetic inhibition by Cd was substantiated by inhibiting ethylene biosynthesis with the use of aminoethoxyvinylglycine (AVG). The suppression of S-assimilation and photosynthetic responses by inhibiting ethylene in GA plus S treated plants under Cd stress indicated the involvement of ethylene in GA-induced S-assimilation and Cd stress alleviation. The outcome of the study is important to unravel the interaction between GA and ethylene and their role in Cd tolerance in plants. [ABSTRACT FROM AUTHOR]