The Low Root Zone Temperature Effects on Nitrogen Fixation, Growth, and Antioxidant Responses of Lentil Inoculated with Rhizobium leguminosarum

Abstract

The plant molecular signals that induce legume-Rhizobium symbiosis are potentially an important source of plant growth promotion in agricultural systems. A study was conducted to evaluate the effects of low root zone temperature (RZT) on nitrogen fixation, antioxidant response, and growth of the lentil plant (Lens culinaris L.), which harbor isoflavonoids that may exert positive impacts on human health, inoculated with R. leguminosarum bv. viciae pre-cultured with additional plant-torhizobia signal compounds (inducers), naringenin (NA), methyl-jasmonate (MJ), and NA+MJ treatment, under greenhouse conditions. Two RZT levels, 20 and 14oC, were maintained through daily irrigations until the plants were harvested 25–30 days after transplantation. The addition of inducer compounds increased the dry weight and leaf greenness of plants under both temperature regimes. Photosynthesis levels were increased significantly (p<0.05) by approximately 12.3% when compared to the group without inducer treatment (control). Nitrogen fixation per plant increased with increasing numbers of nodules. The fixed nitrogen per plant in the NA and NA+MJ treatment groups increased by 18.2 and 20.4% as compared to the controls. No interaction between inducer and temperature factors was detected. Increasing low RZT levels significantly (p<0.05) reduced antioxidant activity, proline content, ascorbate peroxidase, and glutathione reductase contents in the plants treated with induced rhizobia as compared to the controls. Phenol content was recorded as higher at a temperature of 14 than at 20oC, and was significantly (p<0.05) increased in the inducer treatments. These results, collectively, suggest that the pre-incubation of bacterial cells with plant-to-bacteria signal compounds could enhance lentil growth, photosynthetic rates, and nitrogen fixation, and could also alleviate low RZT stress.