Sulfur dioxide (SO2) is a major air pollutant and has significant impacts on plant physiology. Plant can adapt to SO2 stress by controlling stomatal movement, gene expression, and metabolic changes. Here we show clear evidences that SO2-triggered hydrogen peroxide (H2O2) production mediated stomatal closure and cell death in Arabidopsis leaves. High levels of SO2 caused irreversible stomatal closure and decline in guard cell viability, but low levels of SO2 caused reversible stomatal closure. Exogenous antioxidants ascorbic acid (AsA) and catalase (CAT) or Ca2+ antagonists EGTA and LaCl3 blocked SO2-induced stomatal closure and decline in viability. AsA and CAT also blocked SO2-induced H2O2 and elevation. However, EGTA and LaCl3 inhibited SO2-induced increase but did not suppress SO2-induced H2O2 elevation. These results indicate that H2O2 elevation triggered stomatal closure and cell death via signaling in SO2-stimulated Arabidopsis guard cells. NADPH oxidase inhibitor DPI blocked SO2-induced cell death but not the stomatal closure triggered by low levels of SO2, indicating that NADPH oxidase-dependent H2O2 production plays critical role in SO2 toxicity but is not necessary for SO2-induced stomatal closure. Our results suggest that H2O2 production and accumulation in SO2-stimulated plants trigger plant adaptation and toxicity via reactive oxygen species mediating Ca2+ signaling. 1. Introduction Sulfur dioxide (SO2) is a harmful gas that is emitted largely from burning coal, high-sulfur oil, and fuels. During the past few decades, the concentration of SO2 in the atmosphere has increased in many areas of the world, especially in the developing countries. High levels of SO2 can injure many plant species and varieties, resulting in photosynthesis decline, growth inhibition, and even death [1–4]. Sulfur dioxide enters plants mainly through the open stomata [5]. Once it enters the leaf, SO2 is hydrated to form and . The toxicity of SO2 is derived from molecular species sulfite () and bisulfite () generated after SO2 is dissolved in cellular fluid [6]. Sulfite oxidation, which is the detoxification reaction of sulfite to sulfate (), leads to the formation of reactive oxygen species (ROS) in plant cells [7, 8]. The production and accumulation of ROS are one of the key events in plant response to SO2 [9–12]. ROS have been proposed as central components of plant response to both biotic and abiotic stresses. Under such conditions, ROS may play two very different roles: exacerbating damage or signaling the activation of defense responses [13, 14]. It has been
References
[1]
N. M. Darrall, “The effect of air pollutants on physiological processes in plants,” Plant, Cell & Environment, vol. 12, no. 1, pp. 1–30, 1989.
[2]
T. Hogetsu and M. Shishikura, “Effects of sulfur dioxide and ozone on intact leaves and isolated mesophyll cells of groundnut plants (Arachis hypogaea L.),” Journal of Plant Research, vol. 107, no. 3, pp. 229–235, 1994.
[3]
M. Noji, M. Saito, M. Nakamura, M. Aono, H. Saji, and K. Saito, “Cysteine synthase overexpression in tobacco confers tolerance to sulfur-containing environmental pollutants,” Plant Physiology, vol. 126, no. 3, pp. 973–980, 2001.
[4]
R. Rakwal, G. K. Agrawal, A. Kubo et al., “Defense/stress responses elicited in rice seedlings exposed to the gaseous air pollutant sulfur dioxide,” Environmental and Experimental Botany, vol. 49, no. 3, pp. 223–235, 2003.
[5]
H. Rennenberg and C. Herschbach, “Responses of plants to atmospheric sulphur,” in Plant Response to Air Pollution, M. Yunus and M. Iabal, Eds., pp. 285–294, John Wiley & Sons, Chichester, UK, 1996.
[6]
H. Pfanz and U. Heber, “Buffer capacities of leaves, leaf cells, and leaf cell organelles in relation to fluxes of potentially acidic gases,” Plant Physiology, vol. 81, pp. 597–602, 1986.
[7]
K. Asada, “Formation and scavenging of superoxides in chloroplasts, with relation to injury by sulfur dioxide,” Research Report of the National Institute for Environmental Studies, vol. 11, pp. 165–179, 1980.
[8]
N. R. Madamanchi and R. G. Alscher, “Metabolic bases for differences in sensitivity of two pea cultivars to sulfur dioxide,” Plant Physiology, vol. 97, no. 1, pp. 88–93, 1991.
[9]
K. Tanaka, N. Kondo, and K. Sugahara, “Accumulation of hydrogen peroxide in chloroplasts of SO2-fumigated spinach leaves,” Plant and Cell Physiology, vol. 23, no. 6, pp. 999–1007, 1982.
[10]
R. H？nsch and R. R. Mendel, “Sulfite oxidation in plant peroxisomes,” Photosynthesis Research, vol. 86, no. 3, pp. 337–343, 2005.
[11]
E. Giraud, A. Ivanova, C. S. Gordon, J. Whelan, and M. J. Considine, “Sulphur dioxide evokes a large scale reprogramming of the grape berry transcriptome associated with oxidative signalling and biotic defence responses,” Plant, Cell and Environment, vol. 35, no. 2, pp. 405–417, 2012.
[12]
L. Li and H. Yi, “Differential expression of Arabidopsis defense-related genes in response to sulfur dioxide,” Chemosphere, vol. 87, no. 7, pp. 718–724, 2012.
[13]
J. Dat, S. Vandenabeele, E. Vranová, M. van Montagu, D. Inzé, and F. van Breusegem, “Dual action of the active oxygen species during plant stress responses,” Cellular and Molecular Life Sciences, vol. 57, no. 5, pp. 779–795, 2000.
[14]
P. Sharma, A. B. Jha, R. S. Dubey, and M. Pessarakli, “Reactive Oxygen species, oxidative damage, and antioxidative defense mechanism in plants under stressful conditions,” Journal of Botany, vol. 2012, Article ID 217037, 26 pages, 2012.
[15]
S. Neill, R. Desikan, and J. Hancock, “Hydrogen peroxide signalling,” Current Opinion in Plant Biology, vol. 5, no. 5, pp. 388–395, 2002.
[16]
C. Laloi, K. Apel, and A. Danon, “Reactive oxygen signalling: the latest news,” Current Opinion in Plant Biology, vol. 7, no. 3, pp. 323–328, 2004.
[17]
H. B. Shao, L. Y. Chu, Z. H. Lu, and C. M. Kang, “Primary antioxidant free radical scavenging and redox signaling pathways in higher plant cells,” International Journal of Biological Sciences, vol. 4, no. 1, pp. 8–14, 2008.
[18]
R. Mittler, “Oxidative stress, antioxidants and stress tolerance,” Trends in Plant Science, vol. 7, no. 9, pp. 405–410, 2002.
[19]
S.-H. Hung, C.-W. Yu, and C. H. Lin, “Hydrogen peroxide functions as a stress signal in plants,” Botanical Bulletin of Academia Sinica, vol. 46, no. 1, pp. 1–10, 2005.
[20]
L. Li, H. Yi, L. Wang, and X. Li, “Effects of sulfur dioxide on the morphological and physiological biochemical parameters in Arabidopsis thaliana plants,” Journal of Agro-Environment Science, vol. 27, pp. 525–529, 2008.
[21]
A. M. Hetherington, “Guard cell signaling,” Cell, vol. 107, no. 6, pp. 711–714, 2001.
[22]
X. Zhang, L. Zhang, F. C. Dong, J. F. Gao, D. W. Galbraith, and C.-P. Song, “Hydrogen peroxide is involved in abscisic acid-induced stomatal closure in Vicia faba,” Plant Physiology, vol. 126, no. 4, pp. 1438–1448, 2001.
[23]
J. I. Schroeder, G. J. Allen, V. Hugouvieux, J. M. Kwak, and D. Waner, “Guard cell signal transduction,” Annual Review of Plant Biology, vol. 52, pp. 627–658, 2001.
[24]
H. Yi, J. Yin, X. Liu, X. Jing, S. Fan, and H. Zhang, “Sulfur dioxide induced programmed cell death in Vicia guard cells,” Ecotoxicology and Environmental Safety, vol. 78, pp. 281–286, 2012.
[25]
K. Apel and H. Hirt, “Reactive oxygen species: metabolism, oxidative stress, and signal transduction,” Annual Review of Plant Biology, vol. 55, pp. 373–399, 2004.
[26]
R. Desikan, M.-K. Cheung, A. Clarke et al., “Hydrogen peroxide is a common signal for darkness- and ABA-induced stomatal closure in Pisum sativum,” Functional Plant Biology, vol. 31, no. 9, pp. 913–920, 2004.
[27]
N. Suzuki, S. Koussevitzky, R. Mittler, and G. Miller, “ROS and redox signalling in the response of plants to abiotic stress,” Plant, Cell and Environment, vol. 35, no. 2, pp. 259–270, 2012.
[28]
T. Fukao and J. Bailey-Serres, “Plant responses to hypoxia—is survival a balancing act?” Trends in Plant Science, vol. 9, no. 9, pp. 449–456, 2004.
[29]
R. Mittler, S. Vanderauwera, M. Gollery, and F. van Breusegem, “Reactive oxygen gene network of plants,” Trends in Plant Science, vol. 9, no. 10, pp. 490–498, 2004.
[30]
Y. Song, Y. Miao, and C.-P. Song, “Behind the scenes: the roles of reactive oxygen species in guard cells,” New Phytologist, vol. 201, no. 4, pp. 1121–1140, 2014.
[31]
Z.-M. Pel, Y. Murata, G. Benning, et al., “Calcium channels activated by hydrogen peroxide mediate abscisic acid signalling in guard cells,” Nature, vol. 406, no. 6797, pp. 731–734, 2000.
[32]
V. D. Petrov and F. van Breusegem, “Hydrogen peroxide—a central hub for information flow in plant cells,” AoB Plants, vol. 12, no. 1, Article ID pls014, 2012.
[33]
M. A. Torres and J. L. Dangl, “Functions of the respiratory burst oxidase in biotic interactions, abiotic stress and development,” Current Opinion in Plant Biology, vol. 8, no. 4, pp. 397–403, 2005.
[34]
R. Mahalingam and N. Fedoroff, “Stress response, cell death and signalling: the many faces of reactive oxygen species,” Physiologia Plantarum, vol. 119, no. 1, pp. 56–68, 2003.
[35]
I. C. Mori and J. I. Schroeder, “Reactive oxygen species activation of plant Ca2+ channels. A signaling mechanism in polar growth, hormone transduction, stress signaling, and hypothetically mechanotransduction,” Plant Physiology, vol. 135, no. 2, pp. 702–708, 2004.
[36]
D. B. Kiselevsky, Y. E. Kuznetsova, L. A. Vasil'ev et al., “Effect of Ca2+ on programmed death of guard and epidermal cells of pea leaves,” Biochemistry, vol. 75, no. 5, pp. 614–622, 2010.
[37]
R. Errakhi, A. Dauphin, P. Meimoun et al., “An early Ca2+ influx is a prerequisite to thaxtomin A-induced cell death in Arabidopsis thaliana cells,” Journal of Experimental Botany, vol. 59, no. 15, pp. 4259–4270, 2008.
[38]
S. Orrenius, B. Zhivotovsky, and P. Nicotera, “Regulation of cell death: the calcium-apoptosis link,” Nature Reviews Molecular Cell Biology, vol. 4, no. 7, pp. 552–565, 2003.
[39]
F. Van Breusegem and J. F. Dat, “Reactive oxygen species in plant cell death,” Plant Physiology, vol. 141, no. 2, pp. 384–390, 2006.
[40]
M. C. de Pinto, V. Locato, and L. de Gara, “Redox regulation in plant programmed cell death,” Plant, Cell and Environment, vol. 35, no. 2, pp. 234–244, 2012.
[41]
T. Pfannschmidt, K. Br？utigam, R. Wagner, et al., “Potential regulation of gene expression in photosynthetic cells by redox and energy state: approaches towards better understanding,” Annals of Botany, vol. 103, no. 4, pp. 599–607, 2009.
