Pretreatment with H 2 O 2 alleviates aluminum-induced oxidative stress in wheat seedlings

1. Pretreatment with H2O2 alleviates aluminum-induced oxidative stress in wheat seedlings Fang Jie Xu1, Chong Wei Jin1, Wen Jing Liu2, Yong Song Zhang2, Xian Yong Lin1,2* 1Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, 2Zhejiang Key Laboratory of Subtropical Soil Science and Plant Nutrition, College of Environmental & Resources Science, Zhejiang University, Hangzhou 310029, China INTRODUCTION Hydrogen peroxide (H2O2) is a normal reactive oxygen species (ROS) molecule which not only acts as a main cause of oxidative stress, but also involved in signal transduction pathways leading to activation of plant defense against biotic and abiotic stresses. There is growing evidence showed that pretreatment of H2O2 could alleviated the deleterious effects of various stress conditions on plant growth and triggering higher stress tolerance in many plant species. However, to the best of our knowledge, it is still little information about the role of pre-application of H2O2 in activating Al acclimation and its relation to Al tolerant acquisition is still unclear. The present study was aimed at elucidating the effect of H2O2 pretreatment on Al-induced antioxidant responses, including IRE, ROS overproduction, lipid peroxidation, cell death and antioxidant activity increases in two wheat genotypes differing in Al tolerance. RESULTS Figure 1. Relative root elongation of Yangmai-5 and Jian-864 exposed to various concentrations of AlCl3 for 24 h (A) or exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment (B). * indicates significant difference at P < 0.05 and ** indicates a significant difference at P<0.01 between two treatments at each Al concentration. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=20). Figure 4. Activities of SOD (A), CAT (B), POD (C), APX (D), MDHAR (E), DHAR (F), GR (G) and GPX (H) in root tips of Yangmai-5 and Jian-864 exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=3). Figure 2.MDA concentration (A) and Evan blue uptake (B) in root tips of Yangmai-5 and Jian-864 exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=3). Figure 3. Concentrations of O2.- (A) and H2O2 (B) in root tips of Yangmai-5 and Jian-864 exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=3). Figure 5. Concentrations of AsA (A), GSH (B), ratios of AsA/ (AsA+DHA) (C) and GSH/GSSG (D) in root tips of Yangmai-5 and Jian-864 exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=3). CONCLUSIONS • The pretreatment of H2O2 at appropriate time and concentration led to a pronounced alleviation of Al-induced deleterious effects in both wheat genotype during the subsequent Al exposure. Al sensitivity is an important factor affecting the function of H2O2 pretreatment in improving Al acclimation. The H2O2-pretreated increase in Al tolerance is greater in the Al-sensitive wheat genotype (Yangmai-5) as compared to the Al-tolerant wheat genotype (Jian-864). • The pre-application of H2O2 may induce a stronger antioxidant capacity involving higher levels of enzymatic and non-enzymatic antioxidants in root tips of wheat seedlings during subsequent Al exposure, thereby reducing endogenous ROS accumulation and improving Al acclimation of the wheat plants. Therefore, it could be demonstrated that the increased antioxidant defense system level induced by exogenously applied H2O2 acts as the primary factor regulating Al acclimation process in wheat plants. Figure 6. DPPH-radical scavenging activity (A) and FRAP assayed total antioxidant capacities (B) in root tips of Yangmai-5 and Jian-864 exposed to 0 or 30 mM AlCl3 for 24 h, with or without 2 h of 0.6 mM H2O2 pretreatment. Bars (i.e. means) with different letters are significantly different within different genotypes and different treatments (P<0.05, n=3). Acknowledgement This research was financially supported by the National Basic Research Program of China (973 Program, No. 2007CB109305), National Natural Science Foundation of China (grant Nos. 30771292, 30900920, 30270784), the Foundation for University Ph. D. Granting Discipline of the Ministry of Education (grant No. 20060335014) and IPNI. *Corresponding author: xylin@zju.edu.cn