Oxidative Medicine and Cellular Longevity
Volume 2015 (2015), Article ID 397502, 6 pages
http://dx.doi.org/10.1155/2015/397502

Review Article

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

Zhuping Jin1,2 and Yanxi Pei¹

¹School of Life Science, Shanxi University, Taiyuan 030006, China
²School of Chemical Engineering and Environment, North University of China, Taiyuan 030051, China

Received 27 November 2014; Accepted 16 February 2015

Academic Editor: David Pattison

Copyright © 2015 Zhuping Jin and Yanxi Pei. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Recently, overwhelming evidence has proven that hydrogen sulfide (H₂S), which was identified as a gasotransmitter in animals, plays important roles in diverse physiological processes in plants as well. With the discovery and systematic classification of the enzymes producing H₂S in vivo, a better understanding of the mechanisms by which H₂S influences plant responses to various stimuli was reached. There are many functions of H₂S, including the modulation of defense responses and plant growth and development, as well as the regulation of senescence and maturation. Additionally, mounting evidence indicates that H₂S signaling interacts with plant hormones, hydrogen peroxide, nitric oxide, carbon monoxide, and other molecules in signaling pathways.

1. Introduction

Hydrogen sulfide (H₂S) is a colorless, flammable gas with the characteristic odor of rotten eggs. It was widely considered to be just a toxic gas for nearly 300 years mostly due to its unpleasant smell. The breakthrough in the effort to link endogenous H₂S levels and functional changes came when the possible role of H₂S as an endogenous neuromodulator in the brain was reported [1]. The focus on enzymes generating H₂S was another breakthrough in 2001 [2]. The initial work concluded that H₂S was a physiological vasodilator and regulator of blood pressure, which stimulated research on H₂S physiology [3]. In plants, H₂S has been revealed as a crucial player in the regulation of normal plant physiological processes, including seed germination, root morphogenesis, photosynthesis, and flower senescence [4–8]. It was also shown to be an important messenger in plant defense signaling against various abiotic stresses at physiological concentrations [9–13]. In this review, we discuss recent progress that increases our understanding of H₂S synthesis and signaling functions in plants.

2. H₂S Synthesis

In mammalian cells, H₂S is physiologically generated by pyridoxal-5′-phosphate-dependent enzymes, including cystathionine beta-synthase, cystathionine gamma-lyase, and 3-mercaptopyruvate sulfurtransferase (3-MST), during cysteine (Cys) metabolism [3, 14]. H₂S is generated in plants via both enzymatic and nonenzymatic pathways, although the latter only accounts for a small portion of H₂S production. Figure 1, with the enzymes highlighted, demonstrates the production of H₂S in Arabidopsis thaliana.

Figure 1: An overview of H₂S generation in higher plants (adapted from Papenbrock et al., 2007). APS: adenosine 5′-phosphosulfate; Fdred, Fdox: reduced and oxidized ferredoxin; SIR: sulfite reductase.

Several candidate Cys-degrading enzymes have been reported to exist in different plant species (shown in Table 1). In the model plant A. thaliana, the enzymes that produce H₂S can be roughly divided into two categories. One class of these enzymes is Cys desulfhydrases (CDes), which degrade Cys into H₂S, ammonia, and pyruvate in a stoichiometric ratio of 1 : 1 : 1 and require pyridoxal 5′-phosphate as a cofactor [15]. L-Cys desulfhydrase is one of the enzymes that decompose L-Cys and was first discovered in the sulfur metabolism of tobacco cultured cells [16]. D-Cys desulfhydrase 1 specifically uses D-Cys as its substrate, and D-Cys desulfhydrase 2 degrades L/D-Cys simultaneously [17, 18]. The production of H₂S by CDes has been confirmed in various areas of biology [9, 11, 14, 15, 19, 20]. CDes are Cys desulfhydrases with singular functions in desulfuration. Their mRNA levels were significantly higher in the stems and cauline leaves than in the roots, rosette leaves, and flowers of A. thaliana [9].

Table 1: Enzymes and coding genes related to H₂S generation in Arabidopsis.

Substrate
Enzyme
Cellular localization
Locus
Reference

L-Cys
AtLCD
Cytoplasm
At3g62130
[16]

AtNFS1/Nifs1
Mitochondria
At5g65720
[27]

AtNFS2/Nifs2
Plastid
At1g08490
[28]

DES1
Cytoplasm
At5g28030
[24]

OASTL-A1
Cytoplasm
At4g14880
[25]

OASTL-A2
Cytoplasm
At3g22460
[30]

OASTL-B
Plastid
At2g43750
[26]

OASTL-C
Mitochondria
At3g59760
[27]

D-Cys
AtDCD1
Mitochondria
At1g48420
[17]

L/D-Cys
AtDCD2
Mitochondria
At3g26115
[18]

Unknown
PLP-dependent transferase superfamily
Chloroplast
At5g26600
[15]

Unknown
NAC domain containing protein 1
Unknown
At1g01010
[15]

At: Arabidopsis thaliana, Cys: cysteine, DCD: D-Cys desulfhydrase, DES: desulfhydrase, LCD: L-Cys desulfhydrase, NAC: N-acetyl-L-cysteine, NFS: nitrogenase Fe-S cluster, OASTL: O-acetyl-L-serine(thiol)lyase, and PLP: pyridoxal 5′-phosphate.

Another class of the enzymes is O-acetyl-L-serine (thiol) lyase (OAS-TL), which is responsible for the incorporation of inorganic S into Cys, and free H₂S appears to be released only in a minor reaction [21]. During an incubation period, the enzyme formed about 25 times more Cys than H₂S, in a molar ratio, per mg protein [22]. Nine OAS-TL genes have been identified in A. thaliana, which are located in the cytosol, mitochondria, or plastid [23]. Recently, DES1 was reported as a frequent novel L-Cys desulfhydrase, which, based on sequence feature alignments, belongs to the OAS-TL family [24–28]. The Km value for L-Cys in the DES1 reaction is 13-fold lower than that for OAS in the OAS-TL reaction, indicating a much higher affinity of DES1 for L-Cys as a substrate [2]. The biochemical characterization of the T-DNA insertion mutant des1 reveals that the total intracellular Cys concentration increased by approximately 25% [28]. However, as a member of the OAS-TL family, its function in synthesizing H₂S has not been clearly studied. In vitro, the reaction of OAS-TL is a net H₂S-consuming reaction [22]. Thus, the statement that DES1 is the only enzyme involving in the degradation of Cys is open to question [24, 28, 29].

In addition, Nifs/NFS, with L-Cys desulfhydrase-like activity, is also potentially involved in H₂S production [31, 32]. Two genes, At5g26600 and At1g01010, in A. thaliana have been identified that encode proteins with CDes structural features [15], and 3-MST is also related to H₂S production in plants [33].

3. Physiological Functions of H₂S in Plants

H₂S has been reported to play important roles in diverse physiological processes in plants. Research on the endogenous H₂S of higher plants can be traced back to 1978, when H₂S was observed to be released from leaves of cucumber, corn, and soybean [34]. Leaves of older plants contain higher H₂S concentrations than younger plants [35]. A recent study showed that the mRNA levels of CDes were gradually elevated in a developmental stage-dependent manner [9]. The importance of H₂S in the regulation of plant growth, development, and senescence has emerged.

The improvement in seed germination rates due to exogenous H₂S treatments was confirmed. H₂S or HS⁻, rather than other sulfur-containing components derived from the exogenous H₂S donor, NaHS, contributed to the promotion of seed germination [4]. NaHS preferentially affects the activity of endosperm β-amylase and maintains lower levels of malondialdehyde and hydrogen peroxide (H₂O₂) in germinating seeds [7]. In addition, the application of NaHS to seedling cuttings of sweet potato promoted the number and length of adventitious roots [5]. At the same time, H₂S modulates the expression of genes involved in photosynthesis and thiol redox modification to regulate its photosynthesis [36]. It is hypothesized that an increase in the stomatal density also contributes to this process [37]. The osmotic-induced decrease in the chlorophyll concentration could be alleviated by spraying the NaHS solution [6]. H₂S was also found to delay flower opening and senescence in cut flowers and branches [8]. These effects occur in a dose-dependent manner. In the cytosol, H₂S negatively regulates autophagy and modulates the transcriptional profile of A. thaliana using des1 [38]. H₂S strongly affects plant metabolism at most stages of life and causes statistically significant increases in biomass, including higher fruit yields [39].

H₂S also plays pivotal roles in plant responses or adaptation under biotic and abiotic stress conditions. Early studies concerning H₂S emissions in plants were associated with plant responses to pathogens as part of sulfur-induced resistance [40]. In 2008, H₂S was found to be an important cellular signal for the first time, highlighting the protective effect of H₂S against copper stress [4]. Thereafter, a stream of publications on various positive effects of H₂S and H₂S signaling in plants emerged. Soon, H₂S was shown to alleviate the effects of aluminum, cadmium, chromium and boron toxicity, drought and osmotic stress, heat stress, hypoxia, and other stresses [9, 11–13, 20, 41–43]. Most of these reports discussed, as analogies with animal systems, how H₂S signaling is important for plant protection against stress.

Stomatal movement is very important in plant responses to environmental stimuli, and a key target of H₂S signaling in plants is the specialized guard cell. Recent studies have reported that H₂S is responsible for drought stress relief by inducing stomatal closure in A. thaliana [9, 20]. These observations are consistent with a previous report in both Vicia faba and Impatiens walleriana [30]. Similarly, H₂S was confirmed to be a novel downstream indicator of nitric oxide (NO) during ethylene-induced stomatal closure [44]. However, the effect of H₂S on stomatal movement has been a controversial topic. Another research group reported that exogenous H₂S induced stomatal opening by reducing the accumulation of NO in guard cells of A. thaliana and a crop plant, Capsicum annuum [45, 46]. The reasons for these different observations are not clear and require further study. The difference may simply be due to the different experimental materials and methods. The purpose of stomatal closure is to reduce the moisture loss under drought stress, and the induction of stomatal opening is to enhance photosynthesis and reduce the photorespiration.

4. Cross-talk of H₂S with Other Signals

Plants perceive and respond to H₂S, but studies on the mechanisms of H₂S functioning in plant responses to stress are very limited. An overview of our current understanding of plant H₂S signaling is shown in Figure 2. H₂S is particularly active and may interact with and modify numerous other signals. Thus, there may be multiple routes of H₂S perception and signaling to be unraveled.

Figure 2: Generalized model of H₂S signaling in response to abiotic stress in plants. Solid line arrows depict stimulatory effect; dashed cents arrows represent the putative interaction; gray bold rectangle indicates cell membrane. ABA: abscisic acid; CBF: C-repeat binding factor; CO: carbon monoxide; DREB: dehydration responsive element; Eth: ethylene; GA: gibberellic acid; cGMP: cyclic guanosine monophosphate; GSH: glutathione; H₂O₂: hydrogen peroxide; H₂S: hydrogen sulfide; JA: jasmonic acid; NO: nitric oxide; PCD: programmed cell death; RD: responsive to desiccation.

Several lines of evidence point to an interrelationship between H₂S and plant hormones in plant defenses. Abscisic acid (ABA) is produced in large amounts in plants under various abiotic stresses. Under drought stress, the expression of CDes was significantly upregulated, and the production rate of H₂S from these plants also increased [9]. Subsequently, the relationship between H₂S and ABA was reported based on a deficiency of H₂S in the lcd mutant that had a weakened ABA induction of stomatal closure, which indicated that the induction of stomatal closure by ABA was partially dependent on H₂S. As H₂S was also involved in the expression regulation of ion-channel genes, H₂S may be a critical component of ABA-induced stomatal closure via ion channels. At the same time, H₂S influenced the expression of ABA receptors, and the influence of H₂S may have begun upstream of the ABA signaling pathway. Therefore, the above results showed that H₂S interacted with ABA in the stomatal regulation responsible for drought stress in A. thaliana [20]. Indole acetic acid (IAA) showed a rapid increase in different plants treated by exogenous H₂S [5], and ethylene (Eth) could induce H₂S generation [44]. In addition, gibberellic acid (GA) and jasmonic acid (JA) were also involved in the H₂S signal transduction process. H₂S can alleviate the GA-induced programmed cell death in wheat aleurone cells [47], and H₂S may function downstream of H₂O₂ in JA-induced stomatal closure in V. faba [48].

H₂O₂ is another signaling molecule in plants, especially in guard cells. Abiotic stress induces synthesis of both H₂S and H₂O₂; yet it is unclear how these two molecules work in concert in the physiological process. H₂S may represent a novel downstream component of the H₂O₂ signaling cascade during JA-induced stomatal movement in V. faba [48]. Pretreatment of H₂O₂ could improve the germination percentage of Jatropha curcas seeds, and this improvement was mediated by H₂S [49]. These results suggest that H₂O₂ is upstream of H₂S. However, there is plenty of evidence to the contrary. H₂S inhibited the cadmium influx through the plasma membrane calcium channels, which were activated by H₂O₂ [50]. H₂S can participate in enhancing plant resistance to abiotic stress via the improvement of antioxidant systems, such as heavy metal stress, osmotic stress, heat stress, and hypoxia stress [4–7, 10, 42, 43, 49].

Recent evidence suggests that H₂S also plays a role in the NO and carbon monoxide (CO) signaling pathway. In bermudagrass, sodium nitroprusside (SNP, a NO donor) and NaHS combined treatments showed that NO signaling could be blocked by H₂S inhibitors and scavengers, indicating that NO-activated H₂S was essential for the cadmium stress response [51]. Additional evidence showed that both NaHS and GYY4137 reduced the NO accumulation to a large extent in A. thaliana epidermal cells [45]. In sweet potato seedlings, a rapid increase in endogenous H₂S and NO was sequentially observed in shoot tips treated with NaHS. A similar phenomenon in H₂S donor-dependent root organogenesis was observed in both excised willow shoots and soybean seedlings. These results indicated that the process of H₂S-induced adventitious root formation was likely mediated by IAA and NO and that H₂S acts upstream in IAA and NO signaling transduction pathways [5]. Similarly, heme oxygenase 1 functions as a downstream component in H₂S-induced adventitious root formation by the modulation of expression of related genes, which suggested that CO was involved in H2S-induced cucumber adventitious root formation [52].

Additionally, growing evidence suggests that H₂S signaling interacts with calcium (Ca) signaling pathways. Ca²⁺ confers structure and rigidity to the cell wall and regulates plant processes through calmodulin. Li et al. (2013) showed that NaHS pretreatment could improve the entry of extracellular Ca²⁺ into tobacco suspension cultured cells mediated by intracellular calmodulin to increase the heat tolerance [41]. At the level of transcription, the expression of Ca²⁺ channel coding genes decreased, whereas Ca²⁺-ATPase and Ca²⁺-H⁺ cation antiporters were elevated in the lcd mutant. This was in accordance with stronger Ca²⁺ fluorescence in the wild type than in the lcd mutant [20]. These results suggest that Ca signaling plays an important role in the mechanism of H₂S.

Numerous studies showed that, during the enhancement of plant resistance, many substances changed simultaneously. H₂S plays an ameliorative role in protecting plants by increasing the proline content against aluminum toxicity and heat stress [10, 12, 41]. Aluminum-induced citrate secretion was also significantly enhanced by NaHS pretreatment [10]. During the NaHS preincubation period the grain β-amylase activity increased, improving seed germination [7].

5. Conclusions and Perspectives

The mechanisms by which H₂S is generated still remain unresolved, and elucidating how it is made by different plant cells under different conditions is clearly a research priority. H₂S is a key factor in the tolerance of cells to the oxidative stress induced by a range of abiotic conditions, including heavy metal toxicity, drought and osmotic stress, hot stress, hypoxia and other stresses. This probably involves the activation of antioxidant defenses, the induction of stomatal closure, and the enhanced expression of genes encoding resistance-associated enzymes. In these processes, plant hormones, H₂O₂, NO, CO, and Ca signaling participate in H₂S signal transduction, resulting in a complex signaling network.

There are numerous unanswered questions and important areas for further research, concentrated in the following areas. (1) Owing to the promiscuous chemical properties of H₂S, it is problematic to achieve adequate specificity and selectivity for its measurement. At present, the physiological H₂S level was measured by various techniques such as the methylene blue method, monobromobimane, gas chromatography, ion selective electrodes, and fluorescent probes [53]. The diverse detection methods resulted in magnitude differences in measured biological sulfide levels, which will certainly attract increasing attention. (2) The mechanism of H₂S functions performed at the protein level. Until now, a great number of studies focused on protein S-sulfhydration, which is impossible to determine directly by chemical analyses. But in mammals, there have been many results indicating that this process might occur by the transition of intermediate links, such as positional changes and interactions with associated proteins. Moreover, if H₂S can thiolate proteins, it may have the same effect on DNA. (3) Even though H₂S is a short-lived molecule, it is an extremely active one. The mechanisms by which either H₂S or other molecules participating in H₂S signaling function are also important. Thus, elucidation of the H₂S complex signaling network is clearly a research priority.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (31372085 to Yanxi Pei; 31400237 to Zhuping Jin; 31300236 to Zhiqiang Liu) and Shanxi Province Science Foundation for Youths (2014021026-2, to Zhuping Jin).

References

K. Abe and H. Kimura, “The possible role of hydrogen sulfide as an endogenous neuromodulator,” The Journal of Neuroscience, vol. 16, no. 3, pp. 1066–1071, 1996.

W. Zhao, J. Zhang, Y. Lu, and R. Wang, “The vasorelaxant effect of H₂S as a novel endogenous gaseous KATP channel opener,” The EMBO Journal, vol. 20, no. 21, pp. 6008–6016, 2001.

G. Yang, L. Wu, B. Jiang et al., “H₂S as a physiologic vasorelaxant: hypertension in mice with deletion of cystathionine γ-lyase,” Science, vol. 322, no. 5901, pp. 587–590, 2008.

H. Zhang, L.-Y. Hu, K.-D. Hu, Y.-D. He, S.-H. Wang, and J.-P. Luo, “Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress,” Journal of Integrative Plant Biology, vol. 50, no. 12, pp. 1518–1529, 2008.

H. Zhang, J. Tang, X.-P. Liu et al., “Hydrogen sulfide promotes root organogenesis in Ipomoea batatas, Salix matsudana and Glycine max,” Journal of Integrative Plant Biology, vol. 51, no. 12, pp. 1086–1094, 2009.

H. Zhang, Y.-K. Ye, S.-H. Wang, J.-P. Luo, J. Tang, and D.-F. Ma, “Hydrogen sulfide counteracts chlorophyll loss in sweetpotato seedling leaves and alleviates oxidative damage against osmotic stress,” Plant Growth Regulation, vol. 58, no. 3, pp. 243–250, 2009.

H. Zhang, W. Dou, C.-X. Jiang, Z.-J. Wei, J. Liu, and R. L. Jones, “Hydrogen sulfide stimulates β-amylase activity during early stages of wheat grain germination,” Plant Signaling and Behavior, vol. 5, no. 8, pp. 1031–1033, 2010.

H. Zhang, S.-L. Hu, Z.-J. Zhang et al., “Hydrogen sulfide acts as a regulator of flower senescence in plants,” Postharvest Biology and Technology, vol. 60, no. 3, pp. 251–257, 2011.

Z. Jin, J. Shen, Z. Qiao, G. Yang, R. Wang, and Y. Pei, “Hydrogen sulfide improves drought resistance in Arabidopsis thaliana,” Biochemical and Biophysical Research Communications, vol. 414, no. 3, pp. 481–486, 2011.

J. Chen, W.-H. Wang, F.-H. Wu et al., “Hydrogen sulfide alleviates aluminum toxicity in barley seedlings,” Plant and Soil, vol. 362, no. 1-2, pp. 301–318, 2013.

Y.-W. Li, Z.-H. Gong, Y. Mu et al., “An Arabidopsis mutant atcsr-2 exhibits high cadmium stress sensitivity involved in the restriction of H₂S emission,” Journal of Zhejiang University: Science B, vol. 13, no. 12, pp. 1006–1014, 2012.

Z.-G. Li, M. Gong, H. Xie, L. Yang, and J. Li, “Hydrogen sulfide donor sodium hydrosulfide-induced heat tolerance in tobacco (Nicotiana tabacum L) suspension cultured cells and involvement of Ca²⁺ and calmodulin,” Plant Science, vol. 185-186, pp. 185–189, 2012.

H. Zhang, L.-Y. Hu, P. Li, K.-D. Hu, C.-X. Jiang, and J.-P. Luo, “Hydrogen sulfide alleviated chromium toxicity in wheat,” Biologia Plantarum, vol. 54, no. 4, pp. 743–747, 2010.

R. Wang, “Physiological implications of hydrogen sulfide: a whiff exploration that blossomed,” Physiological Reviews, vol. 92, no. 2, pp. 791–896, 2012.

J. Papenbrock, A. Riemenschneider, A. Kamp, H. N. Schulz-Vogt, and A. Schmidt, “Characterization of cysteine-degrading and H₂S-releasing enzymes of higher plants—From the field to the test tube and back,” Plant Biology, vol. 9, no. 5, pp. 582–588, 2007.

H. M. Harrington and I. K. Smith, “Cysteine metabolism in cultured tobacco cells,” Plant Physiology, vol. 65, no. 1, pp. 151–155, 1980.

A. Schmidt, “A cysteine desulfhydrase from spinach leaves specific for D-cysteine,” Zeitschrift für Pflanzenphysiologie, vol. 107, no. 4, pp. 301–312, 1982.

A. Riemenschneider, E. Bonacina, A. Schmidt, and J. Papenbrock, “Remove from marked Records Isolation and characterization of a second D-cysteine desulfhydrase-like protein from Arabidopsis,” in Proceedings of the 6th International Workshop on Plant Sulfur Metabolism: Sulfur Transport and Assimilation in Plants in the Post Genomic Era, K. Saito, L. J. de Kok, I. Stulen et al., Eds., pp. 103–106, Chiba, Japan, 2005.

J. J. Shen, Z. J. Qiao, T. J. Xing et al., “Cadmium toxicity is alleviated by AtLCD and AtDCD in Escherichia coli,” Journal of Applied Microbiology, vol. 113, no. 5, pp. 1130–1138, 2012.

Z. Jin, S. Xue, Y. Luo et al., “Hydrogen sulfide interacting with abscisic acid in stomatal regulation responses to drought stress in Arabidopsis,” Plant Physiology and Biochemistry, vol. 62, no. 1, pp. 41–46, 2013.

C.-H. Tai and P. F. Cook, “O-acetylserine sulfhydrylase,” Advances in Enzymology and Related Areas of Molecular Biology, vol. 74, pp. 185–234, 2000.

P. Burandt, J. Papenbrock, and A. Schmidt, “Genotypical differences in total sulfur contents and cysteine desulfhydrase activities in Brassica napus L.,” Phyton-International Journal of Experimental Botany, vol. 41, no. 1, pp. 75–86, 2001.

C. Álvarez, L. Calo, L. C. Romero, I. García, and C. Gotor, “An O-Acetylserine(thiol)lyase homolog with l-Cysteine desulfhydrase activity regulates cysteine homeostasis in Arabidopsis,” Plant Physiology, vol. 152, no. 2, pp. 656–669, 2010.

M. Wirtz, M. Droux, and R. Hell, “O-acetylserine (thiol) lyase: an enigmatic enzyme of plant cysteine biosynthesis revisited in Arabidopsis thaliana,” Journal of Experimental Botany, vol. 55, no. 404, pp. 1785–1798, 2004.

E. R. Bonner, R. E. Cahoon, S. M. Knapke, and J. M. Jez, “Molecular basis of cysteine biosynthesis in plants: structural and functional analysis of O-acetylserine sulfhydrylase from Arabidopsis thaliana,” The Journal of Biological Chemistry, vol. 280, no. 46, pp. 38803–38813, 2005.

C. Heeg, C. Kruse, R. Jost et al., “Analysis of the Arabidopsis O-acetylserine(thiol)lyase gene family demonstrates compartment-specific differences in the regulation of cysteine synthesis,” Plant Cell, vol. 20, no. 1, pp. 168–185, 2008.

J. M. Jez and S. Dey, “The cysteine regulatory complex from plants and microbes: what was old is new again,” Current Opinion in Structural Biology, vol. 23, no. 2, pp. 302–310, 2013.

L. C. Romero, I. García, and C. Gotor, “L-cysteine desulfhydrase 1 modulates the generation of the signaling molecule sulfide in plant cytosol,” Plant Signaling & Behavior, vol. 8, no. 5, Article ID e24007, 2013.

L. C. Romero, M. Á. Aroca, A. M. Laureano-Marín, I. Moreno, I. García, and C. Gotor, “Cysteine and cysteine-related signaling pathways in Arabidopsis thaliana,” Molecular Plant, vol. 7, no. 2, pp. 264–276, 2014.

C. Gotor, C. Álvarez, M. Á. Bermúdez, I. Moreno, I. García, and L. C. Romero, “Low abundance does not mean less importance in cysteine metabolism,” Plant Signaling and Behavior, vol. 5, no. 8, pp. 1028–1030, 2010.

S. Kushnir, E. Babiychuk, S. Storozhenko et al., “A mutation of the mitochondrial ABC transporter stat1 leads to dwarfism and chlorosis in the Arabidopsis mutant starik,” Plant Cell, vol. 13, no. 1, pp. 89–100, 2001.

S. Léon, B. Touraine, J.-F. Briat, and S. Lobréaux, “The AtNFS2 gene from Arabidopsis thaliana encodes a Nifs-like plastidial cysteine desulphurase,” Biochemical Journal, vol. 366, no. 2, pp. 557–564, 2002.

J. Papenbrock, S. Guretzki, and M. Henne, “Latest news about the sulfurtransferase protein family of higher plants,” Journal of Amino Acids, vol. 41, no. 1, pp. 43–57, 2011.

L. G. Wilson, R. A. Bressan, and P. Filner, “Light-dependent emission of hydrogen sulfide from plants,” Plant Physiology, vol. 61, no. 2, pp. 184–189, 1978.

H. Rennenberg and P. Filner, “Developmental changes in the potential for H₂S emission in cucurbit plants,” Plant Physiology, vol. 71, no. 2, pp. 269–275, 1983.

J. Chen, F.-H. Wu, W.-H. Wang et al., “Hydrogen sulphide enhances photosynthesis through promoting chloroplast biogenesis, photosynthetic enzyme expression, and thiol redox modification in Spinacia oleracea seedlings,” Journal of Experimental Botany, vol. 62, no. 13, pp. 4481–4493, 2011.

B. Duan, Y. Ma, M. Jiang, F. Yang, L. Ni, and W. Lu, “Improvement of photosynthesis in rice (Oryza sativa L.) as a result of an increase in stomatal aperture and density by exogenous hydrogen sulfide treatment,” Plant Growth Regulation, vol. 75, no. 1, pp. 33–44, 2014.

C. Álvarez, I. García, I. Moreno et al., “Cysteine-generated sulfide in the cytosol negatively regulates autophagy and modulates the transcriptional profile in Arabidopsis,” The Plant Cell, vol. 24, no. 11, pp. 4621–4634, 2012.

F. D. Dooley, S. P. Nair, and P. D. Ward, “Increased growth and germination success in plants following hydrogen sulfide administration,” PLoS ONE, vol. 8, no. 4, Article ID e62048, 2013.

E. Bloem, A. Riemenschneider, J. Volker et al., “Sulphur supply and infection with Pyrenopeziza brassicae influence L-cysteine desulphydrase activity in Brassica napus L.,” Journal of Experimental Botany, vol. 55, no. 406, pp. 2305–2312, 2004.

Z.-G. Li, X.-J. Ding, and P.-F. Du, “Hydrogen sulfide donor sodium hydrosulfide-improved heat tolerance in maize and involvement of proline,” Journal of Plant Physiology, vol. 170, no. 8, pp. 741–747, 2013.

W. Cheng, L. Zhang, C. Jiao et al., “Hydrogen sulfide alleviates hypoxia-induced root tip death in Pisum sativum,” Plant Physiology and Biochemistry, vol. 70, pp. 278–286, 2013.

B.-L. Wang, L. Shi, Y.-X. Li, and W.-H. Zhang, “Boron toxicity is alleviated by hydrogen sulfide in cucumber (Cucumis sativus L.) seedlings,” Planta, vol. 231, no. 6, pp. 1301–1309, 2010.

J. Liu, L. Hou, G. Liu, X. Liu, and X. Wang, “Hydrogen sulfide induced by nitric oxide mediates ethylene-induced stomatal closure of Arabidopsis thaliana,” Chinese Science Bulletin, vol. 56, no. 33, pp. 3547–3553, 2011.

M. Lisjak, N. Srivastava, T. Teklic et al., “A novel hydrogen sulfide donor causes stomatal opening and reduces nitric oxide accumulation,” Plant Physiology and Biochemistry, vol. 48, no. 12, pp. 931–935, 2010.

M. Lisjak, T. Teklić, I. D. Wilson, M. E. Wood, M. Whiteman, and J. T. Hancock, “Hydrogen sulfide effects on stomatal apertures,” Plant Signaling and Behavior, vol. 6, no. 10, pp. 1444–1446, 2011.

Y. Xie, C. Zhang, D. Lai et al., “Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression,” Journal of Plant Physiology, vol. 171, no. 2, pp. 53–62, 2014.

Z. Hou, J. Liu, L. Hou, X. Li, and X. Liu, “H₂S may function downstream of H₂O₂ in jasmonic acid-induced stomatal closure in Vicia faba,” Chinese Bulletin of Botany, vol. 46, no. 4, pp. 396–406, 2011.

Z.-G. Li, M. Gong, and P. Liu, “Hydrogen sulfide is a mediator in H₂O₂-induced seed germination in Jatropha Curcas,” Acta Physiologiae Plantarum, vol. 34, no. 6, pp. 2207–2213, 2012.

J. Sun, R. Wang, X. Zhang et al., “Hydrogen sulfide alleviates cadmium toxicity through regulations of cadmium transport across the plasma and vacuolar membranes in Populus euphratica cells,” Plant Physiology and Biochemistry, vol. 65, pp. 67–74, 2013.

H. Shi, T. Ye, and Z. Chan, “Nitric oxide-activated hydrogen sulfide is essential for cadmium stress response in bermudagrass (Cynodon dactylon (L). Pers.),” Plant Physiology and Biochemistry, vol. 74, pp. 99–107, 2014.

Y.-T. Lin, M.-Y. Li, W.-T. Cui, W. Lu, and W.-B. Shen, “Haem oxygenase-1 is involved in hydrogen sulfide-induced cucumber adventitious root formation,” Journal of Plant Growth Regulation, vol. 31, no. 4, pp. 519–528, 2012.

P. Nagy, Z. Pálinkás, A. Nagy, B. Budai, I. Tóth, and A. Vasas, “Chemical aspects of hydrogen sulfide measurements in physiological samples,” Biochimica et Biophysica Acta, vol. 1840, no. 2, pp. 876–891, 2014.