Involvement of antioxidant capacity in quinclorac tolerance in Eleusine indica

The relationship between quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) tolerance and scavenging capacity of reactive oxygen species (ROS) in Eleusine indica was investigated to understand the tolerance mechanisms of E. indica to the herbicide. E. indica was approximately 104-fold more tolerant to quinclorac than Digitaria adscendens based on GR40 (herbicide dose required to cause a 40% reduction in plant growth) values determined 6 days after treatment. Quinclorac (10 μM) induced the overproduction of ROS (presumably superoxide anion (O2−)) in the root tips of D. adscendens 24 h after treatment. On the other hand, 10 μM quinclorac did not induce the ROS production in the roots of E. indica. The inherent superoxide anion scavenging activity (SOSA) was 4.2-fold higher in E. indica than that in D. adscendens. The constitutive activities of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) were 1.9, 4.7, and 3.0 times higher, respectively in E. indica than those in D. adscendens. Exogenously applied H2O2, one of the main ROS, decreased the chlorophyll content in leaf discs of E. indica and D. adscendens. However, the chlorophyll content in E. indica was much higher than that in D. adscendens, indicating that E. indica with its high antioxidant capacity can alleviate H2O2-induced phytotoxicity and is more tolerant to H2O2 than D. adscendens. These results suggest that the high scavenging capacity of ROS in E. indica could be one factor in its tolerance to quinclorac.

► Eleusine indica is tolerant to the herbicide quinclorac, and Digitaria adscendens is susceptible to quinclorac.
► Quinclorac induced ROS overproduction in roots of D. adscendens, but not in E. indica.
► The inherent superoxide anion scavenging activity was much higher in E. indica than that in D. adscendens.
► The constitutive activities of CAT, APX, and GR were also much higher in E. indica than those in D. adscendens.
► E. indica can alleviate H2O2-induced phytotoxicity and is more tolerant to H2O2 than D. adscendens.