Metabolism of reactive oxygen species involved in increasing root vigour of cotton seedlings by soaking seeds with mepiquat chloride

Abstract

The plant growth regulator, mepiquat chloride (1,1-dimethylpiperidinium chloride, DPC) has been used worldwide to suppress excessive growth in cotton plants. It also increases the root vigour of cotton plants. To reveal the possible role of reactive oxygen species (ROS) involved, we conducted a experiment to investigate the effect of soaking seed with 200 mg L-1 mepiquat chloride (DPC) on root vigour of cotton (Gossypium hirsutum L.) seedlings by using a cotton cv. Guoxin 3. The results showed that soaking seed with DPC could significantly increase the root vigour of cotton seedlings with two expanded cotyledons. Root viability estimated by 2,3,5-triphenyl tetrazolium chloride (TTC) reduction and root respiratory rate were increased by 167% and 90% in DPC treatment. The average OD of in situ TTC staining in DPC treated root tips was 0.3-fold higher than that of control. At 300 μm from the root apex away, DPC treatment resulted in a 36% increase of net K+ influx. The result of acridine orange staining suggested that seedlings treated with DPC had less apoptotic cells in root elongation zone compared with control. In addition, DPC treatment significantly altered the activities of antioxidant enzyme and ROS accumulation in roots of cotton seedlings. Catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were enhanced, but superoxide dismutase (SOD) was reduced, which therefore resulted in 56% less H2O2 accumulation and lighter diaminobenzidine staining (H2O2 histochemical detection in situ) in roots compared with control. Another type of ROS, O2-, its production rate also decreased by 65% in roots treated with DPC. Taken together, we speculated that the increased root vigour of cotton seedlings by soaking seed with DPC may be partially explained by improvement of ROS metabolism.