Rhizobial symbiosis alleviates polychlorinated biphenyls-induced systematic oxidative stress via brassinosteroids signaling in alfalfa.
The role of symbiotic rhizobia in the alleviation of polychlorinated biphenyl (PCB)-induced phytotoxicity in alfalfa and the brassinosteroid (BR) hormone signaling involved were investigated during phytoremediation. The association between alfalfa and Sinorhizobium meliloti was adopted as a remediation model. Phytotoxicity due to PCB 77 (3,3',4,4'-tetrachlorobiphenyl) exerted adverse impacts on plant performance (biomass accumulation and photosynthesis) and elicited cellular oxidative stress (overproduction of reactive oxygen species, lipid peroxidation, and cell necrosis) which was largely attenuated by pre-inoculation with S. meliloti strain NM. The protective role may have been achieved as a result of strengthening of basic antioxidant defense before stress as evidenced by the augmented activity and gene expression of antioxidative enzymes (peroxidase, glutathione reductase, superoxide dismutase, catalase, and ascorbate peroxidase) of both leaves and roots. In nodulated seedlings peroxidase showed additive increased activity following PCB exposure but the activities of the other four enzymes tended to remain stable after stress. Furthermore, application of strain NM and brassinolide both triggered the accumulation of endogenous BRs and the antioxidant network, while pre-treatment of seedlings with a biosynthetic inhibitor of BRs, brassinazole, abolished the rhizobia-induced activation of detoxification responses towards PCB. These observations indicate that association with S. meliloti NM enhanced the systemic antioxidant defenses of alfalfa to detoxify PCB, at least in part, via BR-dependent signaling pathways. These results contribute to our knowledge of the 'logistic role' played by rhizobia in assisting the phytoremediation of PCB-contaminated soils and suggest an optimum manipulation strategy for bioremediation.
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Xiaomi
X
Wang
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: yteng@issas.ac.cn.
Ying
Y
Teng
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Ning
N
Zhang
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Peter
P
Christie
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Zhengao
Z
Li
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Yongming
Y
Luo
Chongqing Research Academy of Environmental Sciences, Chongqing 401147, China.
Jun
J
Wang
D000975:Antioxidants / Q000502:physiology; D001673:Biodegradation, Environmental; D060406:Brassinosteroids / Q000494:pharmacology*; D000455:Medicago sativa / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects*; D011078:Polychlorinated Biphenyls / Q000009:adverse effects*; D012231:Rhizobium; D013559:Symbiosis
D000975:Antioxidants; D060406:Brassinosteroids; D011078:Polychlorinated Biphenyls
Antioxidant defense; Bioremediation; Brassinosteroids; Medicago sativa; ROS; Rhizobia