Kun Yan 1,2 Xingyuan He 1 Wei Chen 1 Tao Lu 1 Sheng Xu 1 Hongbo Shao 2,3 Guoyou Zhang 1,4 1 Department of Urban Forest, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, P. R. China 2 Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, P. R. China 3 Institute of Life Sciences, Qingdao University of Science and Technology, Qingdao, P. R. China 4 Laboratory of International Plant Resources, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan Research Article Variation of Antioxidant System in Pinus armandii under Elevated O 3 in an Entire Growth Season Impact of elevated O 3 (80 nmol mol 1 ) was studied on antioxidant system in the previous-year needles (P-needles) of Pinus armandii under the background of global climate change. CAT (catalase) did not play an important role in defensing O 3 pollution, as no significant change was observed in its activity in P-needles exposed to elevated O 3 during the entire growth season. Ascorbate (AsA) was more sensitive to elevated O 3 , as the O 3 -induced decrease in its content was observed at Day 45. It suggests that AsA consumption was a crucial way for protecting against O 3 pollution. After 75 days of O 3 exposure, increase in superoxide dismutase and ascorbate peroxidase activities occurred in P-needles (p < 0.05), whereas glutathione reductase activity was significantly increased after 105 days of O 3 treatment (p < 0.05). Dehydroascorbate reductase and monoascorbate reductase activities also increased after 75 days of elevated O 3 exposure. However, the elevated antioxidant capability did not suppress the generation of reactive oxygen species, and as a result, increase in malondialdehyde content was noted (p < 0.05). Noticeably, no change was observed in electrolyte leakage during the entire growth season under elevated O 3 fumigation. It indicates that O 3 -induced oxidative stress was not severe in the needles of P. armandii. In other words, P. armandii has certain tolerance to O 3 pollution. Keywords: Biomarker; East Asia; Global climate change; Lipid peroxidation Received: April 11, 2012; revised: May 28, 2012; accepted: June 7, 2012 DOI: 10.1002/clen.201200161 1 Introduction Ground-level background O 3 concentration has been increasing to current level of 20–45 nmol mol 1 in the middle latitude northern hemisphere since pre-industrial times, and this rising trend is expected to persist throughout the century to levels in the range of 42–84 nmol mol 1 by 2100 due to the increased emission of O 3 precursors [1]. Especially in China, anthropogenic emission of O 3 precursors have increased significantly due to rapid urbanization and industrialization, compared with a great reduction in Europe and mild variation in North America [2–4]. Ozone is a phytotoxic air pollutant which can increase the gener- ation of reactive oxygen species (ROS) in plant cell [5–7]. Antioxidant system regulating ROS concentration in plants plays a crucial role in response to high environmental O 3 [8]. Antioxidant system consists of antioxidant enzymes and antioxidants. The most abundant anti- oxidant is ascorbate (AsA). Superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) are ROS-scavenging enzymes, while glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monoascorbate reductase (MDAR) act as antioxidant- regenerating enzymes. AsA works as substrate for APX to scavenge hydrogen peroxide and also can directly clear ROS [5, 7, 9]. The positive role of AsA is demonstrated by the higher O 3 -sensitivity in the mutants without AsA synthesis capacity [10] and by plant overexpressing AsA oxidase [11]. SOD cooperates with APX and CAT to scavenge superoxide anion radical and hydrogen peroxide and then limits the production of hydroxyl radical, which can avoid danger- ous oxidative damage in plant cell [5, 7, 12]. DHAR, MDAR, and GR cooperate to regenerate glutathione and AsA from their oxidized forms at the expense of reducing power [12]. In previous studies, increase in antioxidants content or antioxidant enzymes activities was widely reported in broadleaf trees as well as conifers under O 3 exposure (e.g., [13, 14]), as O 3 stimulated the antioxidant defense capability in plants. In contrast, it has been found that O 3 decreased antioxidant capacity in Laurus nobilis leaves and Picea abies needles [14, 15]. Besides, high O 3 did not affect antioxidant content in Pinus canariensis needles [16]. Much work has been done to explore how elevated O 3 affect trees distributed in North America and Mediterranean area, but the endemic tree species in East Asia has not been well concerned. So far, studies on the effects of elevated O 3 have mainly focused on important crops such as wheat and rice in Asia [17–19], since it is still a crucial issue to provide enough food for the countries with great Additional correspondence: X. He, e-mail: hexy@iae.ac.cn Correspondence: Prof. H. Shao, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China E-mail: shaohongbochu@126.com Abbreviations: AA, ambient air; AsA, ascorbate; APX, ascorbate peroxidase; CAT, catalase; DHAR, dehydroascorbate reductase; DW, dry weight; EL, electrolyte leakage; EO, elevated O 3 ; GR, glutathione reductase; MDA, malondialdehyde; MDAR, monoascorbate reductase; OTC, open top chamber; P-needles, previous-year needles; ROS, reactive oxygen species; SOD, superoxide dismutase 5 ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com 2013, 41 (1), 5–10