Hydrogen sulfide in plants: from dissipation of excess sulfur to signaling molecule.

Nitric Oxide xxx (2014) xxx–xxx

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Hydrogen sulfide in plants: From dissipation of excess sulfur to signaling molecule Alexander Calderwood a, Stanislav Kopriva a,b,⇑ a b

Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK Institute of Botany and Cluster of Excellence on Plant Sciences (CEPLAS), University of Cologne, Germany

a r t i c l e

i n f o

Article history: Available online xxxx Keywords: Hydrogen sulfide Plants Sulfate assimilation Cysteine Signaling

a b s t r a c t Sulfur is essential in all organisms for the synthesis of amino acids cysteine and methionine and as an active component of numerous co-factors and prosthetic groups. However, only plants, algae, fungi, and some prokaryotes are capable of using the abundant inorganic source of sulfur, sulfate. Plants take sulfate up, reduce it, and assimilate into organic compounds with cysteine being the first product of the pathway and a donor of reduced sulfur for synthesis of other S-containing compounds. Cysteine is formed in a reaction between sulfide, derived from reduction of sulfite and an activated amino acid acceptor, O-acetylserine. Sulfide is thus an important intermediate in sulfur metabolism, but numerous other functions in plants has been revealed. Hydrogen sulfide can serve as an alternative source of sulfur for plants, which may be significant in anaerobic conditions of waterlogged soils. On the other hand, emissions of hydrogen sulfide have been detected from many plant species. Since the amount of H2S discharged correlated with sulfate supply to the plants, the emissions were considered a mechanism for dissipation of excess sulfur. Significant hydrogen sulfide emissions were also observed in plants infected with pathogens, particularly with fungi. H2S thus seems to be part of the widely discussed sulfur-induced-resistance/sulfur-enhanced-defense. Recently, however, more evidence has emerged for a role for H2S in regulation and signaling. Sulfide stabilizes the cysteine synthase complex, increasing so the synthesis of its acceptor O-acetylserine. H2S has been implicating in regulation of plant stress response, particularly draught stress. There are more and more examples of processes regulated by H2S in plants being discovered, and hydrogen sulfide is emerging as an important signaling molecule, similar to its role in the animal and human world. How similar the functions, and homeostasis of H2S are in these diverse organisms, however, remains to be elucidated. Ó 2014 Elsevier Inc. All rights reserved.

Introduction The field of gaseous signal transmitters is relatively new in biology and rapidly expanding. The discovery of nitric oxide (NO) in animals and its function in cellular signaling has been a major breakthrough inspiring a whole new research field [1–3]. The area has been expanding in two directions; NO has been found to be important outside the animal kingdom, in plants [4,5] and yeast [6], and secondly, other gaseous signals have been discovered, namely carbon monoxide (CO) [7] and hydrogen sulfide (H2S) [8]. In contrast to NO, whose effect on living organisms has been revealed only recently, CO and H2S have been long known for their toxicity and their function in signaling is an exciting new

⇑ Corresponding author. Address: Institute of Botany, University of Cologne, Zülpicher Str. 47b, 50674 Köln, Germany. E-mail address: [email protected] (S. Kopriva).

development. Similar to NO, research on H2S signaling has rapidly developed with a large number of highly significant contributions. The recent opening of the Nitric Oxide journal to research on H2S [9] is a clear demonstration of the momentum in H2S research, as is the increased interest in H2S signaling in the plant research community [10,11]. In plants, NO has been recognized and investigated in detail solely for its roles in signaling. This indeed appears to be its only function in plants. The new signaling molecule, H2S, however, is a compound long known to plant scientists, and interest in H2S was initially driven by its phytotoxic effects and its function in plant sulfur metabolism. Over the years, new functions for this gas have been recognized; as a mechanism for dissipation of excess sulfur, an alternative S source in plant nutrition, and most recently in regulation and signaling. Several excellent reviews pointed out the various roles H2S plays in plants and proposed that it may be an important signal, similar to NO [10,11]. Here we discuss these

http://dx.doi.org/10.1016/j.niox.2014.02.005 1089-8603/Ó 2014 Elsevier Inc. All rights reserved.

Please cite this article in press as: A. Calderwood, S. Kopriva, Hydrogen sulfide in plants: From dissipation of excess sulfur to signaling molecule, Nitric Oxide (2014), http://dx.doi.org/10.1016/j.niox.2014.02.005

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A. Calderwood, S. Kopriva / Nitric Oxide xxx (2014) xxx–xxx

different functions of H2S in plants, the evolution of our view on this important gas, and critically review recent literature describing the diverse positive effects of H2S on plant growth and stress tolerance. H2S as an intermediate of assimilatory sulfate reduction Sulfur is essential for all living organisms as a key constituent of the amino acids cysteine and methionine, as well as cofactors, polysaccharides, lipids and iron–sulfur clusters. Plants (along with fungi and prokaryotes) are the assimilators, which reduce and incorporate inorganic sulfur, which is almost entirely available as oxidized sulfate, into organic forms via the reductive sulfate assimilation pathway [12]. The first step of sulfur utilization by plants is, therefore, the uptake of inorganic sulfate by sulfate transporters. Once in the epidermis, sulfate is transferred to central cylinder via plasmodesmata between cells. However sulfate can leak into apoplast, which is also thought to be important in sulfur distribution. This is likely via an as yet unidentified passive transport mechanism driven by the outside-positive gradient of membrane potential at the plasma membrane. Once within a cell, sulfate is either stored in the vacuole, or metabolized immediately [12,13]. Using the energy of ATP hydrolysis, sulfate is activated to form adenosine 50 -phosphosulfate (APS) by adenylation. This reaction is catalysed by ATP sulfurylase (ATPS). The high-energy phosphate– sulfate mixed anhydride bond produced makes further enzymatic catalysis highly favourable, however it also makes the APS synthesis very unfavourable, with the equilibrium constant strongly favouring the reverse reaction. In plants, APS synthesis is driven forward by coupling it to hydrolysis of the pyrophosphate product, and rapidly removing APS. In contrast to animals, plants are able to reduce activated sulfate in the plastid to sulfite using APS reductase (APR). Sulfite is then further reduced to sulfide by ferredoxin dependent sulfite reductase (SiR), and sulfide is finally incorporated into O-acetylserine (OAS) to form cysteine, the direct or indirect precursor of all organic compounds containing reduced sulfur in plants or animals. This is the assimilatory sulfate reduction pathway, (Fig. 1), by which sulfur enters primary metabolism, it is essential for survival, and cannot be compensated for by any other enzymatic process [12]. The sulfide formed by sulfite reductase is incorporated into OAS by O-acetylserine thiol lyase (OAS-TL) forming cysteine. OAS is itself synthesized from serine and acetyl-coenzyme-A by serine

acetyltransferase (SAT) [14]. Under normal conditions cysteine synthesis is limited by OAS rather than sulfide levels as the concentration of OAS is found to be far below the K OAS m of OAS-TL isoforms, whereas sulfide concentration in the chloroplast and cytosol is higher than K sulfide [15]. Interestingly, whereas sulfide is produced m exclusively in the plastids, cysteine synthesis takes place in all three proteogenic organelles. Three major OAS-TL and three major SAT isoforms are located in the plastid, cytosol and mitochondria [16–18]. Although each compartment is capable of producing sufficient cysteine to sustain growth, under normal conditions the bulk of the specific steps in cysteine synthesis are localized predominantly in different compartments. A coordinated interplay is necessary to assure that sulfide generated in plastids can react in the cytosol with OAS generated by mitochondria. The biological significance of this division of labor is, however, not known. The ability of plants to grow with a single SAT or OAS-TL shows clearly that OAS, sulfide and cysteine are freely transferrable between compartments. For mitochondrial cysteine synthesis, sulfide is thus capable of moving across four membranes. It has been suggested that H2S might diffuse across the chloroplast envelope [19], but the stroma of the chloroplast is at pH 8.5 under illumination [20], at which 95% of sulfide would be in the charged HS form, and only poorly able to traverse lipid bilayers, therefore a protein transporter is likely. Such protein ‘‘bound’’ sulfide can be a direct substrate for OAS-TL and was part of a previously postulated ‘‘bound intermediate’’ pathway of sulfate assimilation [21], based on detection of intermediates of sulfate assimilation bound to proteins and a thiosulfonate reductase activity measured in algal extracts [22]. Whether free or bound, H2S is an essential metabolite in plant cells and absolutely required for their survival. Knockdown mutant lines with reduced activity of sulfite reductase exhibit strongly retarded growth, and this enzyme is now considered to be a ‘‘bottleneck’’ in reductive sulfate assimilation that cannot be compensated for by any other enzymatic process [23]. However, probably because of this essential function, sulfite reductase is not regulated to the same extent as APS reductase [12,16] which is considered the key regulatory step of the pathway [24], or the cysteine synthase complex, which is responsible for utilization of sulfide for cysteine synthesis [25]. The essential role of sulfate assimilation in plants and the central position of H2S as pathway intermediate is however a landmark against which all other potential functions of H2S have to be measured and carefully evaluated for their biological significance. H2S production in plants Apart from sulfite reductase, there are at least four other enzymes capable of H2S production (Fig. 2). OAS-TL, which synthesizes cysteine from OAS and sulfide can catalyse the reverse reaction, and produce H2S from cysteine. This was demonstrated in potatoes with reduced OAS-TL activity which also showed lower

Fig. 1. Assimilatory sulfate reduction in plants. The scheme shows the localization of the individual reactions of sulfate assimilation. The activated sulfate, APS, represents a branch point between primary and secondary sulfur metabolism as it can also be phosphorylated by APS kinase (APK) to form 30 -phosphoadenosine 50 -phosphosulfate (PAPS), which acts as a donor of activated sulfate, and is involved in the modification of a variety of proteins, saccharides and secondary metabolites such as glucosinolates (GLS) [97].

Fig. 2. Enzymes producing and consuming H2S in plants. Enzyme names are in italics: SiR, sulfite reductase, OAS-TL, OAS thiollyase, DES1, cysteine desulfhydrase, CAS, cyanoalanine synthase, DCDES, D-cysteine desulfhydrase. The main pathway of H2S homeostasis is represented by bold arrows.



capacity to release H2S [26]. Two other H2S producing enzymes also belong to the OAS-TL gene family. L-cysteine desulfhydrase (DES1) metabolizes cysteine into H2S, pyruvate and ammonium [27,28]. The biological function of this enzyme seems to be regulation of cysteine homeostasis [28]. The second, b-cyanoalanine synthase uses cysteine to detoxify cyanide with H2S as a by-product [29,30]. Cyanide is formed during synthesis of ethylene and is a potent inhibitor of respiratory chain, therefore, b-cyanoalanine synthase is present in mitochondria [30,31]. Another player in plant H2S homeostasis is a D-cysteine desulfhydrase, which similar to DES1 produces pyruvate, ammonium, and H2S [32]. Interestingly, even though the substrates differ only in chirality, the two proteins, L-cysteine- and D-cysteine desulfhydrase, are not related except that they both use pyridoxal phosphate as co-factor. The physiological function of D-cysteine and D-cysteine desulfhydrase is, however, not known. While all of these enzymes are capable of H2S production, only OAS-TL seems to be able to assimilate H2S. Also the H2S producers differ in their capability to rapidly induce an H2S ‘‘burst’’ as would be expected for its function in signaling. H2S release by b-cyanoalanine synthase and D-cysteine desulfhydrase is dependent on substrates that are found in low concentration in plant cells, and so their role in H2S homeostasis remains to be clarified. H2S in plant nutrition As discussed, the major source of sulfur for plants is sulfate in the soil, but plants are also capable of utilizing other sulfur sources, namely various sulfur containing gases in the atmosphere. Traditionally, these comprised sulfur dioxide and H2S, which were major atmospheric pollutants before the 1980s and there is a large body of literature describing the phytotoxic effects of H2S, e.g., [33,34]. The way that plants cope with exposure to these toxic gases is largely by their assimilation into organic sulfur compounds, although other detoxification mechanisms also exist [35–37]. Thus, exposure to SO2 leads to both increased reduction of the gas to sulfide and synthesis of cysteine and glutathione [38]. However, some of the SO2 is oxidized to sulfate by sulfite oxidase [39,40]. H2S, on the other hand, is mostly assimilated into the thiols [41]. The rapid assimilation of the gases is important, as they quickly cause the accumulation of reactive oxygen species and oxidative stress. The increased synthesis of cysteine, with sulfide as an intermediate, thus serves two purposes; reducing the active concentration of the gases in leaves, and also making more glutathione available to protect against oxidative stress. Exposure to SO2 or H2S has consequences for the whole of sulfur nutrition. Increased availability of cysteine in the fumigated plants reduces demand for sulfate uptake and reduction, and indeed, sulfate uptake and APS reductase are down-regulated in SO2 or H2S exposed plants [35,37,41,42]. Interestingly, the effects of fumigation and the mechanisms of the regulation differ in individual plant species [43]. Generally, however, fumigation with H2S alleviates syndromes of sulfate starvation [42]. Plants grown in nutrient solution without sulfate sustain growth when simultaneously exposed to H2S. The H2S assimilated in the leaves can thus provide sufficient sulfur for synthesis of proteins and all other cellular components necessary for growth, and can be considered as a nutrient. Indeed, in some ecosystems H2S is a significant, if not the major source of environmental sulfur [34]. Analysis of S isotopes revealed that in many marsh plants and sea grasses more than 50% of sulfur originates from H2S. However this H2S is not atmospheric, but originates in the soil through the anaerobic metabolism of bacteria [34]. Thus, while the function of H2S as a nutrient and source of sulfur for plant growth may be

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marginal for the traditional plants and crops, it is highly important in specific soils and ecosystems. H2S as a mechanism for dissipation of excess sulfur Investigation of sulfur nutrition has made interesting progression over the years. In the 1970s and 80s it was dominated by studies of the metabolism of excess sulfur, resulting in a dedicated Annual Review in 1984 [44]. This coincided with a period of heavy air pollution due to the burning of fossil fuels with high sulfur content and inadequate purification procedures. From the mid 80s however, the amount of sulfur emissions declined due to environmental legislation. This had significant effects on sulfur supply to agricultural land, which was previously met by atmospheric deposits, but became inadequate, leading to frequent occurrence of sulfur deficiency and need for sulfur fertilization [45]. This in turn sparkled an interest in the effects of sulfur deficiency on plant metabolism which became a highly investigated area by systems biology methods [46–49]. H2S is central for the question of the fate of excess sulfur. Plants are able to emit H2S from the leaves in response to feeding with sulfate or sulfite, particularly into detached leaves or through injured roots [50]. The emissions can be reduced by feeding the precursor of cysteine, OAS [51]. The source of emitted H2S is the reduction of sulfite in the sulfate assimilation, because the emissions are dependent on light and are also greater in plants fed with sulfite that with sulfate [50]. Thus, plants seem to emit H2S when the rate of sulfate reduction exceeds the rate of provision of carbon skeletons for cysteine synthesis. However, an excess of reduced sulfur can also lead to H2S emissions [52]. H2S was emitted from leaves fed with cysteine, liberated either by the reverse reaction of OAS-TL or by L-cysteine desulfhydrase [52]. H2S emission as a mechanism to dissipate excess sulfur is thus very important to prevent accumulation of sulfite and sulfide, potential triggers of oxidative stress and of cysteine, which in high concentration would affect the cellular redox balance. H2S in plant defense The treatment with excess sulfur however, is not the only condition triggering emissions of H2S. Plant resistance to pathogens and diseases has been linked with the sulfur nutritional status of the plants, as sulfur deficient plants are more susceptible to pathogens, this observation has led to formulation of the concept of ‘‘Sulfur Induced Resistance (SIR)’’ or ‘‘Sulfur Enhanced Defense (SED)’’ [53–55]. There are multiple mechanisms that contribute to the positive effect of sulfur on plant health, including increased synthesis of glutathione, which is important for defense against reactive oxygen species [56]. Additionally, many plants synthesize sulfur-containing natural products with a role in pathogen defense, the best known examples are glucosinolates [57] in the Brasicaceae and alliins in onion and garlic [58]. Another important mechanism is H2S emission. The protective effects of H2S have been long known, e.g. a reduction in number of nematodes present [59]. Although the source of the gas in these experiments on flooded rice fields was not plants, but microbes, several lines of evidence point to a major role of H2S emissions in SIR. In field experiments, H2S emissions correlated with fungal infection [53,60]. Higher emissions upon controlled inoculation with fungi is consistent with the SIR and SED concepts [60]. In addition, the activity of DES1, the enzyme most probably responsible for the bulk of H2S production is increased in infected plants and is higher in plants with sufficient sulfur supply than in S-deficient ones [61]. It seems therefore, that


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H2S is at least part of the mechanism of SIR or SED and protects plants against pathogens. H2S as a metabolic signal of sulfur status The recent interest in H2S is however triggered not by its metabolic functions but because of its potential role in cellular signaling. There is a solid evidence that it is indeed involved in the regulation of activity of cysteine synthase multi-enzyme complex, which is formed by oligomerization of SAT and OAS-TL [62]. In Arabidopsis free homohexameric SAT is a dimer of trimers, this is assumed to form the hexameric core of the complex, which is then bound by two OAS-TL dimers [63]. Complex formation strongly affects subunit activity. SAT activity is increased; in fact so far all detected SAT activity is associated with the complex bound form [64]. However the increased activity of SAT in complex is not due to augmented reaction kinetics, in fact in vitro SAT exhibits slightly lower substrate affinity in complex [15], instead reduced feedback sensitivity to cysteine means that the enzyme is no longer inhibited [62,65]. In contrast, OAS-TL is active when free from bound SAT [64], and its activity decreases in the complex, as the SAT Cterminus binds to the catalytic groove of OAS-TL, and blocks substrate access to catalytic residues [66]. This inhibition excludes substrate channeling as the purpose of the synthase complex, instead, at least in the mitochondria, is thought to function as a sensor for sulfur status [12,62]; the complex is stabilized by sulfide, and destabilized by OAS [64,67]. During sulfur deprivation, sulfide concentration declines, and OAS accumulates, triggering dissociation of complex, and reduction in SAT activity, resulting in feedback to maintain homeostatic levels of sulfide and OAS. The relative importance of sulfide versus OAS in this regulatory loop is unclear, although given that sulfide must be maintained at low concentration in the mitochondria to prevent inactivation of cytochrome c oxidase [68], it seems likely that OAS concentration may be the dominant factor. Nevertheless, its contribution to regulation of cysteine synthase assembly makes H2S one of the few clearly defined components of the sulfur starvation response. H2S and signaling Once H2S was found to be an important cellular signal in humans and animals, it was only a matter of time before H2S signaling would be described in plants. Indeed, in 2008 the first report highlighting the protective effect of H2S against copper stress appeared [69] and initiated a stream of publications on various positive effects of H2S and H2S signaling in plants. Soon H2S was shown to alleviate effects of aluminum, cadmium and boron toxicity, drought and osmotic stress, hypoxia and many more stresses [70–74]. Most of these reports discussed, in analogy with animal systems, how H2S signaling is important for plant protection against these stresses. However, it has to be noted that for all of these reports of H2S signaling in stress defense, there are equally valid alternative explanations. Treatment with H2S increases the availability of reduced sulfur for synthesis of glutathione, the major player in defense against a wide range of stresses. Increased glutathione synthesis protects against cadmium and other kinds of oxidative stress [56,75]. So, while the positive effects of H2S are not questionable, their attribution to H2S signaling is far from certain, even if H2S treatment leads to changes in gene expression, that in turn improves stress tolerance [76]. While the link between the changes in expression of defense genes and H2S is attractive as a confirmation of the H2S role in signaling, it is well known that these defense genes are regulated by changes in glutathione levels [77], so again, an alternative explanation is possible.

These reports thus require very careful consideration and revisiting before unequivocally assigning the protective effect of H2S to cellular signaling. Experiments with inhibitors of glutathione synthesis to distinguish between effects of H2S alone and downstream metabolites would be a good start to such efforts. The diverse positive effects of H2S on plant stress tolerance described above were encapsulated by a recent report showing that treatment with low doses of H2S improves plant growth and germination. Dooley et al. [78] showed that treatment with H2S in concentrations of 10–100 lM increases size and fresh weight of several plant species both in hydroculture and in soil. H2S also had a positive effect on germination, particularly at 100 lM, and on growth of leaf disks floated on aqueous solution [78]. Treatment with H2S also resulted in increased yield of wheat. The mechanism(s) behind these growth promoting effects of H2S are completely unknown. If confirmed, such a simple means of increasing growth would have an enormous impact on agriculture, however, as the effects of H2S cannot be explained, the report has to be considered cautiously. There is no indication of the nutritional status of the plants; most experiments seem to be performed using water vs. aqueous H2S, i.e. without any mineral nutrients [78]. The jury for this potential breakthrough is therefore still out. However, other processes have been shown to be affected by H2S, where its signaling function is much better characterized. Stomata are responsible for a gas exchange between the plant and the surrounding atmosphere so a gaseous signal affecting this exchange seems logical. Indeed, NO has been shown to have a specific role in the regulation of stomata opening by ABA [79,80] and increased NO production causes stomata closure. But NO has not remained the only gaseous signal in regulation of stomata opening. Studies of epidermal strips revealed that H2S induces stomata closure and that inhibition of H2S production partially blocks the ABA effect on stomata [81]. Interestingly, another report showed the opposite, an increased stomata opening upon increased H2S production [82]. In the light of several reports associating H2S production with drought tolerance [73,83], it seems that increased stomata closure as a result of H2S treatment is a more probable outcome. This has been confirmed by analysis of lcd mutant with reduced H2S accumulation, as these mutants show an increased stomatal aperture in untreated mature leaves and are more sensitive to drought stress [84]. The LCD gene encodes a PLP-binding protein with possible L-cysteine desulfurase activity, but in this line the T-DNA is inserted downstream the gene and disturbs also expression of another gene with unknown function. Therefore there is not enough evidence to mark the LCD protein as another H2S producing enzyme [84]. The mechanism of action on stomata aperture is not clear, although it seems that H2S acts via regulation of ABC channels [81]. Although similarly to NO, H2S seems to be involved in the pathway of ABA-driven stomata closure, as stomata aperture is larger in ABA treated lcd mutants than in wild type plants [84]. The interplay between ABA and H2S is complicated, as e.g. aba3 mutants possess lower capacity for H2S production, and may also involve NO, because treatment with H2S donors reduced NO accumulation in guard cells [82]. To add to the complexity, H2S also interacts with the effects of ethylene on stomata [85]. Thus, there is clearly a demand for detailed dissection of the role H2S plays in regulation of stomata opening, for a thorough dissection of the interplay of ABA, NO, and H2S and also for the clarification of the opposite effects of H2S reported in different experiments. The final area where H2S plays an important role is common to plants and animals. Autophagy is a catabolic process in which lysozymes degrade various cellular components, in order to ensure efficient nutrient recycling, particularly during starvation [86,87]. In plants this process is particularly important for senescence and pathogen defense [88]. The mechanisms of autophagy have



been well characterized in yeast and animal systems [87], which has helped to achieve similar progress in the plant world [88–90]. The involvement of H2S in autophagy was first demonstrated with colon cells, where H2S exposure induced increased formation of LC3B(+) autophagic vacuoles and acidic vesicular organelles, characteristic features of autophagy [91]. Interestingly, two other reports showed the opposite, an inhibition of autophagy by H2S [92,93]. As all three reports investigated different tissues and diseases, it is possible that the effects of H2S on autophagy are cell-type specific. In the plant world, the link between H2S and autophagy has been found by a systematic functional analysis of the OAS-TL family [28]. A mutant of the DES1 isoform showed signs of premature senescence, including the expression of senescence associated genes [28]. Accordingly, senescence associated vacuoles and increased accumulation of autophagy marker protein ATG8 were detected in leaves of des1 mutants but not wild type leaves [94]. Both phenotypes were reversed by treatment with Na2S, and treatment with H2S prevented a carbon starvation induced autophagy, confirming that it is the availability of H2S that affects the autophagy process [94]. H2S thus seems to function as inhibitor of autophagy, which may explain the finding of autophagy related proteins, such as Joka2, in sulfur starved plants as sulfide is one of the first metabolites to decrease in concentration upon S starvation [95].

Conclusions H2S is indeed an enigmatic molecule. It may be the single most important compound for origin of life on Earth [96] and has plethora functions in all observed organisms. H2S has become one of the most studied molecules in animal signaling and the number of open questions and controversies concerning its concentration, effects on various processes and mechanism of action ensure that H2S research will boom further. In plants, the situation is different because H2S importance has long been recognized, but at the same time reminiscent in terms of controversies and both known and unknown unknowns. The dissection of mechanisms of H2S signaling and/or influence on plants is difficult due to its rapid binding to proteins, metabolization to cysteine, and effects on redox homeostasis, which is very difficult to distinguish from the effects of its downstream metabolites cysteine and glutathione. However, given the huge progress the H2S field has achieved in the last decade, we can look forward with optimism to the future which will soon bring a much more detailed understanding of the mechanisms of function of H2S in plants. References [1] J. Bradbury, Medicine nobel prize awarded to US pharmacologists, Lancet 352 (1998) 1287. [2] L.J. Ignarro, G.M. Buga, K.S. Wood, R.E. Byrns, G. Chaudhuri, Endotheliumderived relaxing factor produced and released from artery and vein is nitric oxide, Proc. Natl. Acad. Sci. U.S.A. 84 (1987) 9265–9269. [3] R.M. Palmer, A.G. Ferrige, S. Moncada, Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor, Nature 327 (1987) 524–526. [4] M. Delledonne, Y. Xia, R.A. Dixon, C. Lamb, Nitric oxide functions as a signal in plant disease resistance, Nature 394 (1998) 585–588. [5] J. Durner, D. Wendehenne, D.F. Klessig, Defense gene induction in tobacco by nitric oxide, cyclic GMP, and cyclic ADP-ribose, Proc. Natl. Acad. Sci. U.S.A. 95 (1998) 10328–10333. [6] B. Almeida, S. Buttner, S. Ohlmeier, A. Silva, A. Mesquita, B. Sampaio-Marques, N.S. Osorio, A. Kollau, B. Mayer, C. Leao, J. Laranjinha, F. Rodrigues, F. Madeo, P. Ludovico, NO-mediated apoptosis in yeast, J. Cell Sci. 120 (2007) 3279–3288. [7] L. Xue, G. Farrugia, S.M. Miller, C.D. Ferris, S.H. Snyder, J.H. Szurszewski, Carbon monoxide and nitric oxide as coneurotransmitters in the enteric nervous system: evidence from genomic deletion of biosynthetic enzymes, Proc. Natl. Acad. Sci. U.S.A. 97 (2000) 1851–1855. [8] Y. Kimura, H. Kimura, Hydrogen sulfide protects neurons from oxidative stress, FASEB J. 18 (2004) 1165–1167.

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[9] N. Hogg, Nitric oxide expands scope to cover hydrogen sulfide and carbon monoxide, Nitric Oxide 35 (2013) 1. [10] M. Lisjak, T. Teklic, I.D. Wilson, M. Whiteman, J.T. Hancock, Hydrogen sulfide: environmental factor or signalling molecule?, Plant Cell Environ 36 (2013) 1607–1616. [11] C. Garcia-Mata, L. Lamattina, Gasotransmitters are emerging as new guard cell signaling molecules and regulators of leaf gas exchange, Plant Sci. 201–202 (2013) 66–73. [12] H. Takahashi, S. Kopriva, M. Giordano, K. Saito, R. Hell, Sulfur assimilation in photosynthetic organisms: molecular functions and regulations of transporters and assimilatory enzymes, Annu. Rev. Plant Biol. 62 (62) (2011) 157–184. [13] H. Takahashi, Regulation of sulfate transport and assimilation in plants, Int. Rev. Cell Mol. Biol. 281 (2010) 129–159. [14] M. Wirtz, R. Hell, Functional analysis of the cysteine synthase protein complex from plants: structural, biochemical and regulatory properties, J. Plant Physiol. 163 (2006) 273–286. [15] S. Krueger, A. Niehl, M.C. Lopez Martin, D. Steinhauser, A. Donath, T. Hildebrandt, L.C. Romero, R. Hoefgen, C. Gotor, H. Hesse, Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis, Plant Cell Environ. 32 (2009) 349–367. [16] S. Kopriva, S.G. Mugford, C. Matthewman, A. Koprivova, Plant sulfate assimilation genes: redundancy versus specialization, Plant Cell Rep. 28 (2009) 1769–1780. [17] C. Heeg, C. Kruse, R. Jost, M. Gutensohn, T. Ruppert, M. Wirtz, R. Hell, Analysis of the Arabidopsis O-acetylserine(thiol)lyase gene family demonstrates compartment-specific differences in the regulation of cysteine synthesis, Plant Cell 20 (2008) 168–185. [18] M. Watanabe, K. Mochida, T. Kato, S. Tabata, N. Yoshimoto, M. Noji, K. Saito, Comparative genomics and reverse genetics analysis reveal indispensable functions of the serine acetyltransferase gene family in Arabidopsis, Plant Cell 20 (2008) 2484–2496. [19] M. Wirtz, R. Hell, The role of cellular compartmentation for sulfur amino acid biosynthesis, Amino Acids 33 (2007). Xxxvii-Xxxvii. [20] H.W. Heldt, K. Werdan, M. Milovanc, G. Geller, Alkalization of chloroplast stroma caused by light-dependent proton flux into thylakoid space, Biochim. Biophys. Acta 314 (1973) 224–241. [21] S. Kopriva, A. Koprivova, Plant adenosine 50 -phosphosulphate reductase: the past, the present, and the future, J. Exp. Bot. 55 (2004) 1775–1783. [22] A. Schmidt, Sulfate reduction in a cell-free system of Chlorella. The ferredoxin dependent reduction of a protein-bound intermediate by a thiosulfonate reductase, Arch. Mikrobiol. 93 (1973) 29–52. [23] M.S. Khan, F.H. Haas, A.A. Samami, A.M. Gholami, A. Bauer, K. Fellenberg, M. Reichelt, R. Hansch, R.R. Mendel, A.J. Meyer, M. Wirtz, R. Hell, Sulfite reductase defines a newly discovered bottleneck for assimilatory sulfate reduction and is essential for growth and development in Arabidopsis thaliana, Plant Cell 22 (2010) 1216–1231. [24] U. Scheerer, R. Haensch, R.R. Mendel, S. Kopriva, H. Rennenberg, C. Herschbach, Sulphur flux through the sulphate assimilation pathway is differently controlled by adenosine 50 -phosphosulphate reductase under stress and in transgenic poplar plants overexpressing gamma-ECS, SO, or APR, J. Exp. Bot. 61 (2010) 609–622. [25] M. Wirtz, M. Droux, R. Hell, O-acetylserine (thiol) lyase: an enigmatic enzyme of plant cysteine biosynthesis revisited in Arabidopsis thaliana, J. Exp. Bot. 55 (2004) 1785–1798. [26] A. Riemenschneider, K. Riedel, R. Hoefgen, J. Papenbrock, H. Hesse, Impact of reduced O-acetylserine(thiol)lyase isoform contents on potato plant metabolism, Plant Physiol. 137 (2005) 892–900. [27] H.M. Harrington, I.K. Smith, Cysteine metabolism in cultured tobacco cells, Plant Physiol. 65 (1980) 151–155. [28] C. Alvarez, L. Calo, L.C. Romero, I. Garcia, C. Gotor, An O-acetylserine(thiol)lyase homolog with L-cysteine desulfhydrase activity regulates cysteine homeostasis in Arabidopsis, Plant Physiol. 152 (2010) 656–669. [29] T.N. Akopyan, A.E. Braunstein, E.V. Goryachenkova, Beta-cyanoalanine synthase: purification and characterization, Proc. Natl. Acad. Sci. U.S.A. 72 (1975) 1617–1621. [30] Y. Hatzfeld, A. Maruyama, A. Schmidt, M. Noji, K. Ishizawa, K. Saito, Betacyanoalanine synthase is a mitochondrial cysteine synthase-like protein in spinach and Arabidopsis, Plant Physiol. 123 (2000) 1163–1171. [31] A.G. Warrilow, M.J. Hawkesford, Cysteine synthase (O-acetylserine (thiol) lyase) substrate specificities classify the mitochondrial isoform as a cyanoalanine synthase, J. Exp. Bot. 51 (2000) 985–993. [32] A. Riemenschneider, R. Wegele, A. Schmidt, J. Papenbrock, Isolation and characterization of a D-cysteine desulfhydrase protein from Arabidopsis thaliana, FEBS J. 272 (2005) 1291–1304. [33] C.R. Thompson, G. Kats, Effects of continuous hydrogen sulphide fumigation on crop and forest plants, Environ. Sci. Technol. 12 (1978) 550–553. [34] L.P. Lamers, L.L. Govers, I.C. Janssen, J.J. Geurts, M.E. Van der Welle, M.M. Van Katwijk, T. Van der Heide, J.G. Roelofs, A.J. Smolders, Sulfide as a soil phytotoxin-a review, Front Plant Sci. 4 (2013) 268. [35] D. Yarmolinsky, G. Brychkova, R. Fluhr, M. Sagi, Sulfite reductase protects plants against sulfite toxicity, Plant Physiol. 161 (2013) 725–743. [36] C.E. Stuiver, L.J. De Kok, Atmospheric H(2)S as sulfur source for Brassica oleracea: kinetics of H(2)S uptake and activity of O-acetylserine (thiol)lyase as affected by sulfur nutrition, Environ. Exp. Bot. 46 (2001) 29–36.


6


[37] A. Riemenschneider, V. Nikiforova, R. Hoefgen, L.J. De Kok, J. Papenbrock, Impact of elevated H(2)S on metabolite levels, activity of enzymes and expression of genes involved in cysteine metabolism, Plant Physiol. Biochem. 43 (2005) 473–483. [38] C. Brunold, W. Landolt, P. Lavanchy, SO2 and assimilatory sulfate reduction in beech leaves, Physiol. Plant. 59 (1983) 313–318. [39] G. Brychkova, Z. Xia, G. Yang, Z. Yesbergenova, Z. Zhang, O. Davydov, R. Fluhr, M. Sagi, Sulfite oxidase protects plants against sulfur dioxide toxicity, Plant J. 50 (2007) 696–709. [40] T. Eilers, G. Schwarz, H. Brinkmann, C. Witt, T. Richter, J. Nieder, B. Koch, R. Hille, R. Hansch, R.R. Mendel, Identification and biochemical characterization of Arabidopsis thaliana sulfite oxidase. A new player in plant sulfur metabolism, J. Biol. Chem. 276 (2001) 46989–46994. [41] M. Durenkamp, L.J. De Kok, Impact of pedospheric and atmospheric sulphur nutrition on sulphur metabolism of Allium cepa L., a species with a potential sink capacity for secondary sulphur compounds, J. Exp. Bot. 55 (2004) 1821– 1830. [42] A. Koralewska, C.E.E. Stuiver, F.S. Posthumus, S. Kopriva, M.J. Hawkesford, L.J. De Kok, Regulation of sulfate uptake, expression of the sulfate transporters Sultr1;1 and Sultr1;2, and APS reductase in Chinese cabbage (Brassica pekinensis) as affected by atmospheric H(2)S nutrition and sulfate deprivation, Funct. Plant Biol. 35 (2008) 318–327. [43] M. Durenkamp, L.J. De Kok, S. Kopriva, Adenosine 50 -phosphosulphate reductase is regulated differently in Allium cepa L. and Brassica oleracea L. upon exposure to H2S, J. Exp. Bot. 58 (2007) 1571–1579. [44] H. Rennenberg, The fate of excess sulfur in higher plants, Annu. Rev. Plant Physiol. 35 (1984) 121–153. [45] E. Schnug, E.J. Evans, Monitoring of the sulfur supply of agricultural crops in northern Europe, Phyton 32 (1992) 119–122. [46] M.Y. Hirai, T. Fujiwara, M. Awazuhara, T. Kimura, M. Noji, K. Saito, Global expression profiling of sulfur-starved Arabidopsis by DNA macroarray reveals the role of O-acetyl-l-serine as a general regulator of gene expression in response to sulfur nutrition, Plant J. 33 (2003) 651–663. [47] M.Y. Hirai, M. Klein, Y. Fujikawa, M. Yano, D.B. Goodenowe, Y. Yamazaki, S. Kanaya, Y. Nakamura, M. Kitayama, H. Suzuki, N. Sakurai, D. Shibata, J. Tokuhisa, M. Reichelt, J. Gershenzon, J. Papenbrock, K. Saito, Elucidation of gene-to-gene and metabolite-to-gene networks in arabidopsis by integration of metabolomics and transcriptomics, J. Biol. Chem. 280 (2005) 25590–25595. [48] V. Nikiforova, J. Freitag, S. Kempa, M. Adamik, H. Hesse, R. Hoefgen, Transcriptome analysis of sulfur depletion in Arabidopsis thaliana: interlacing of biosynthetic pathways provides response specificity, Plant J. 33 (2003) 633– 650. [49] A. Maruyama-Nakashita, E. Inoue, A. Watanabe-Takahashi, T. Yamaya, H. Takahashi, Transcriptome profiling of sulfur-responsive genes in Arabidopsis reveals global effects of sulfur nutrition on multiple metabolic pathways, Plant Physiol. 132 (2003) 597–605. [50] L.G. Wilson, R.A. Bressan, P. Filner, Light-dependent emission of hydrogen sulfide from plants, Plant Physiol. 61 (1978) 184–189. [51] H. Rennenberg, Role of o-acetylserine in hydrogen sulfide emission from pumpkin leaves in response to sulfate, Plant Physiol. 73 (1983) 560–565. [52] J. Sekiya, A. Schmidt, L.G. Wilson, P. Filner, Emission of hydrogen sulfide by leaf tissue in response to L-Cysteine, Plant Physiol. 70 (1982) 430–436. [53] E. Bloem, S. Haneklaus, I. Salac, P. Wickenhauser, E. Schnug, Facts and fiction about sulfur metabolism in relation to plant-pathogen interactions, Plant Biol (Stuttg) 9 (2007) 596–607. [54] J. Papenbrock, A. Riemenschneider, A. Kamp, H.N. Schulz-Vogt, A. Schmidt, Characterization of cysteine-degrading and H2S-releasing enzymes of higher plants-from the field to the test tube and back, Plant Biol. (Stuttg) 9 (2007) 582–588. [55] T. Rausch, A. Wachter, Sulfur metabolism: a versatile platform for launching defence operations, Trends Plant Sci. 10 (2005) 503–509. [56] G. Noctor, C.H. Foyer, ASCORBATE AND GLUTATHIONE: keeping active oxygen under control, Annu. Rev. Plant Physiol. Plant Mol. Biol. 49 (1998) 249–279. [57] B.A. Halkier, J. Gershenzon, Biology and biochemistry of glucosinolates, Annu. Rev. Plant Biol. 57 (2006) 303–333. [58] M.G. Jones, J. Hughes, A. Tregova, J. Milne, A.B. Tomsett, H.A. Collin, Biosynthesis of the flavour precursors of onion and garlic, J. Exp. Bot. 55 (2004) 1903–1918. [59] R. Rodriguez-Kabana, J.W. Jordan, J.P. Hollis, Nematodes: biological control in rice fields: role of hydrogen sulfide, Science 148 (1965) 524–526. [60] E. Bloem, S. Haneklaus, J. Kesselmeier, E. Schnug, Sulfur fertilization and fungal infections affect the exchange of H(2)S and COS from agricultural crops, J. Agric. Food Chem. 60 (2012) 7588–7596. [61] E. Bloem, A. Riemenschneider, J. Volker, J. Papenbrock, A. Schmidt, I. Salac, S. Haneklaus, E. Schnug, Sulphur supply and infection with Pyrenopeziza brassicae influence L-cysteine desulphydrase activity in Brassica napus L, J. Exp. Bot. 55 (2004) 2305–2312. [62] M. Wirtz, K.F.M. Beard, C.P. Lee, A. Boltz, M. Schwarzlander, C. Fuchs, A.J. Meyer, C. Heeg, L.J. Sweetlove, R.G. Ratcliffe, R. Hell, Mitochondrial cysteine synthase complex regulates O-acetylserine biosynthesis in plants, J. Biol. Chem. 287 (2012) 27941–27947. [63] M. Wirtz, H. Birke, C. Heeg, C. Muller, F. Hosp, C. Throm, S. Konig, A. FeldmanSalit, K. Rippe, G. Petersen, R.C. Wade, V. Rybin, K. Scheffzek, R. Hell, Structure and function of the hetero-oligomeric cysteine synthase complex in plants, J. Biol. Chem. 285 (2010) 32810–32817.

[64] M. Droux, M.L. Ruffet, R. Douce, D. Job, Interactions between serine acetyltransferase and O-acetylserine (thiol) lyase in higher plants – Structural and kinetic properties of the free and bound enzymes, Eur. J. Biochem. 255 (1998) 235–245. [65] M. Droux, Plant serine acetyltransferase: new insights for regulation of sulphur metabolism in plant cells, Plant Physiol. Biochem. 41 (2003) 619–627. [66] J.A. Francois, S. Kumaran, J.M. Jez, Structural basis for interaction of Oacetylserine sulfhydrylase and serine acetyltransferase in the Arabidopsis cysteine synthase complex, Plant Cell 18 (2006) 3647–3655. [67] O. Berkowitz, M. Wirtz, A. Wolf, J. Kuhlmann, R. Hell, Use of biomolecular interaction analysis to elucidate the regulatory mechanism of the cysteine synthase complex from Arabidopsis thaliana, J. Biol. Chem. 277 (2002) 30629– 30634. [68] H. Birke, F.H. Haas, L.J. De Kok, J. Balk, M. Wirtz, R. Hell, Cysteine biosynthesis, in concert with a novel mechanism, contributes to sulfide detoxification in mitochondria of Arabidopsis thaliana, Biochem. J. 445 (2012) 275–283. [69] H. Zhang, L.Y. Hu, K.D. Hu, Y.D. He, S.H. Wang, J.P. Luo, Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress, J. Integr. Plant Biol. 50 (2008) 1518–1529. [70] H. Zhang, Z.Q. Tan, L.Y. Hu, S.H. Wang, J.P. Luo, R.L. Jones, Hydrogen sulfide alleviates aluminum toxicity in germinating wheat seedlings, J. Integr. Plant Biol. 52 (2010) 556–567. [71] J. Sun, R. Wang, X. Zhang, Y. Yu, R. Zhao, Z. Li, S. Chen, Hydrogen sulfide alleviates cadmium toxicity through regulations of cadmium transport across the plasma and vacuolar membranes in Populus euphratica cells, Plant Physiol. Biochem. 65 (2013) 67–74. [72] B.L. Wang, L. Shi, Y.X. Li, W.H. Zhang, Boron toxicity is alleviated by hydrogen sulfide in cucumber (Cucumis sativus L.) seedlings, Planta 231 (2010) 1301– 1309. [73] Z. Jin, J. Shen, Z. Qiao, G. Yang, R. Wang, Y. Pei, Hydrogen sulfide improves drought resistance in Arabidopsis thaliana, Biochem. Biophys. Res. Commun. 414 (2011) 481–486. [74] W. Cheng, L. Zhang, C. Jiao, M. Su, T. Yang, L. Zhou, R. Peng, R. Wang, C. Wang, Hydrogen sulfide alleviates hypoxia-induced root tip death in Pisum sativum, Plant Physiol. Biochem. 70 (2013) 278–286. [75] A. Koprivova, S. Kopriva, D. Jager, B. Will, L. Jouanin, H. Rennenberg, Evaluation of transgenic poplars over-expressing enzymes of glutathione synthesis for phytoremediation of cadmium, Plant Biol. 4 (2002) 664–670. [76] A. Christou, G.A. Manganaris, I. Papadopoulos, V. Fotopoulos, Hydrogen sulfide induces systemic tolerance to salinity and non-ionic osmotic stress in strawberry plants through modification of reactive species biosynthesis and transcriptional regulation of multiple defence pathways, J. Exp. Bot. 64 (2013) 1953–1966. [77] L. Ball, G.P. Accotto, U. Bechtold, G. Creissen, D. Funck, A. Jimenez, B. Kular, N. Leyland, J. Mejia-Carranza, H. Reynolds, S. Karpinski, P.M. Mullineaux, Evidence for a direct link between glutathione biosynthesis and stress defense gene expression in Arabidopsis, Plant Cell 16 (2004) 2448–2462. [78] F.D. Dooley, S.P. Nair, P.D. Ward, Increased growth and germination success in plants following hydrogen sulfide administration, PLoS ONE 8 (2013) e62048. [79] C. Garcia-Mata, L. Lamattina, Nitric oxide induces stomatal closure and enhances the adaptive plant responses against drought stress, Plant Physiol. 126 (2001) 1196–1204. [80] S.J. Neill, R. Desikan, A. Clarke, J.T. Hancock, Nitric oxide is a novel component of abscisic acid signaling in stomatal guard cells, Plant Physiol. 128 (2002) 13– 16. [81] C. Garcia-Mata, L. Lamattina, Hydrogen sulphide, a novel gasotransmitter involved in guard cell signalling, New Phytol. 188 (2010) 977–984. [82] M. Lisjak, N. Srivastava, T. Teklic, L. Civale, K. Lewandowski, I. Wilson, M.E. Wood, M. Whiteman, J.T. Hancock, A novel hydrogen sulfide donor causes stomatal opening and reduces nitric oxide accumulation, Plant Physiol. Biochem. 48 (2010) 931–935. [83] J. Shen, T. Xing, H. Yuan, Z. Liu, Z. Jin, L. Zhang, Y. Pei, Hydrogen sulfide improves drought tolerance in Arabidopsis thaliana by MicroRNA expressions, PLoS ONE 8 (2013) e77047. [84] Z. Jin, S. Xue, Y. Luo, B. Tian, H. Fang, H. Li, Y. Pei, Hydrogen sulfide interacting with abscisic acid in stomatal regulation responses to drought stress in Arabidopsis, Plant Physiol. Biochem. 62 (2013) 41–46. [85] Z. Hou, L. Wang, J. Liu, L. Hou, X. Liu, Hydrogen sulfide regulates ethyleneinduced stomatal closure in Arabidopsis thaliana, J. Integr. Plant Biol. 55 (2013) 277–289. [86] J.D. Rabinowitz, E. White, Autophagy and metabolism, Science 330 (2010) 1344–1348. [87] D.J. Klionsky, Autophagy: from phenomenology to molecular understanding in less than a decade, Nat. Rev. Mol. Cell Biol. 8 (2007) 931–937. [88] Y. Liu, D.C. Bassham, Autophagy: pathways for self-eating in plant cells, Annu. Rev. Plant Biol. 63 (2012) 215–237. [89] F. Li, R.D. Vierstra, Autophagy: a multifaceted intracellular system for bulk and selective recycling, Trends Plant Sci. 17 (2012) 526–537. [90] A.R. Thompson, R.D. Vierstra, Autophagic recycling: lessons from yeast help define the process in plants, Curr. Opin. Plant Biol. 8 (2005) 165–173. [91] Y.C. Wu, X.J. Wang, L. Yu, F.K. Chan, A.S. Cheng, J. Yu, J.J. Sung, W.K. Wu, C.H. Cho, Hydrogen sulfide lowers proliferation and induces protective autophagy in colon epithelial cells, PLoS ONE 7 (2012) e37572.


A. Calderwood, S. Kopriva / Nitric Oxide xxx (2014) xxx–xxx [92] F. Talaei, V.M. van Praag, R.H. Henning, Hydrogen sulfide restores a normal morphological phenotype in Werner syndrome fibroblasts, attenuates oxidative damage and modulates mTOR pathway, Pharmacol. Res. 74 (2013) 34–44. [93] D. Wang, Y. Ma, Z. Li, K. Kang, X. Sun, S. Pan, J. Wang, H. Pan, L. Liu, D. Liang, H. Jiang, The role of AKT1 and autophagy in the protective effect of hydrogen sulphide against hepatic ischemia/reperfusion injury in mice, Autophagy 8 (2012) 954–962. [94] C. Alvarez, I. Garcia, I. Moreno, M.E. Perez-Perez, J.L. Crespo, L.C. Romero, C. Gotor, Cysteine-generated sulfide in the cytosol negatively regulates

7

autophagy and modulates the transcriptional profile in Arabidopsis, Plant Cell 24 (2012) 4621–4634. [95] K. Zientara-Rytter, J. Lukomska, G. Moniuszko, R. Gwozdecki, P. Surowiecki, M. Lewandowska, F. Liszewska, A. Wawrzynska, A. Sirko, Identification and functional analysis of Joka2, a tobacco member of the family of selective autophagy cargo receptors, Autophagy 7 (2011) 1145–1158. [96] J.L. Bada, New insights into prebiotic chemistry from Stanley Miller’s spark discharge experiments, Chem. Soc. Rev. 42 (2013) 2186–2196. [97] S. Kopriva, S.G. Mugford, P. Baraniecka, B.R. Lee, C.A. Matthewman, A. Koprivova, Control of sulfur partitioning between primary and secondary metabolism in Arabidopsis, Front Plant Sci. 3 (2012) 163.


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Hydrogen sulfide in signaling pathways.

Role of cGMP in hydrogen sulfide signaling.

Biogenesis of reactive sulfur species for signaling by hydrogen sulfide oxidation pathways.

Emergence of hydrogen sulfide as an endogenous gaseous signaling molecule in cardiovascular disease.

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Signaling molecules: hydrogen sulfide and polysulfide.

Hydrogen sulfide and polysulfides as signaling molecules.

Bioconversion of high concentrations of hydrogen sulfide to elemental sulfur in airlift bioreactor.

Fluorescent probes for hydrogen sulfide (H2S) and sulfane sulfur and their applications to biological studies.

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Hydrogen sulfide production from subgingival plaque samples.

Toxicology of hydrogen sulfide.

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Hydrogen sulfide interacts with calcium signaling to enhance the chromium tolerance in Setaria italica.

Carbon Monoxide as a Signaling Molecule in Plants.

Analysis of some enzymes activities of hydrogen sulfide metabolism in plants.

Consecutive oxygen-for-sulfur exchange reactions between vanadium oxide cluster anions and hydrogen sulfide.

Effective sulfur and energy recovery from hydrogen sulfide through incorporating an air-cathode fuel cell into chelated-iron process.

Physiological Implications of Hydrogen Sulfide in Plants: Pleasant Exploration behind Its Unpleasant Odour.

Chemical tools for the study of hydrogen sulfide (H2S) and sulfane sulfur and their applications to biological studies.