Cross-talk between antioxidant production and secondary metabolite biosynthesis under combined effects of ozone stress and nitrogen amendments: A case study of lemongrass.

The present experiment was done to study the interactive effects of soil nitrogen (N) amendments and elevated ozone (O3) (N-O3) on a medicinal plant, lemongrass [Cymbopogon flexuosus (Steud.) (Wats.)]. The experiment used two doses of inorganic soil nitrogen (N1, recommended and N2, 1.5-times recommended dose) in open-top chambers under ambient and elevated (ambient + 15 ppb and ambient + 30 ppb) O3 conditions. To analyze various characteristics, samples were collected at 45 and 90 days after transplantation (DAT). Additionally, at 110 days after transplantation (DAT), the metabolite contents of the leaves and essential oils were analyzed. The present study aims to investigate the mechanistic approach involving the crosstalk between antioxidant production and secondary metabolite biosynthesis in lemongrass upon N-O3 interactions. The present experiment showed that N amendments can be an efficient measure to manage O3 injury in plants, along with ensuring a balance between primary and secondary metabolic pathways, thus sustaining the plant defense and production of bioactive compounds, simultaneously. Under N-O3, not only the Halliwell asada pathway was stimulated resulting in the increased activities and concentrations of antioxidant pools; the shikimate, phenylpropanoid and mevalonic acid pathways were also invigorated, producing more number and contents of secondary metabolites (SMs), compared with plants that were not treated with N doses. This study suggests that soil nitrogen amendments will improve the therapeutic qualities of lemongrass, along with the strengthening of its antioxidant machinery, upon exposure to O3 stress.

Using soil nitrogen amendments in mitigating ozone stress in agricultural crops: a case study of cluster beans.

The climate change scenario in the coming years is liable to have serious negative consequences on agricultural productivity. Increasing tropospheric ozone concentration is an important aspect of climate change, which, due to its oxidative nature, is injurious to the plants. Due to the multifarious nature and continuously increasing concentration of tropospheric ozone, it is prerequisite to develop strategies to manage ozone stress in plants. Present study not only evaluates the potential of soil nitrogen amendments in ameliorating ozone stress in plants, but also focuses upon the mechanistic approaches adopted by the different plant cultivars to combat ozone stress. Three doses of nitrogen amendments, recommended (N1), 1.5× recommended (N2) and 2× recommended (N3), were given to two cultivars (S-151 and PUSA-N) of Cymopsis tetragonoloba exposed to ambient ozone stress. Control plants were also maintained in which no nitrogen treatment was given. Nitrogen supplementation reduced the root nodulation frequency and leghaemoglobin content, which subsequently increased the cellular nitrogen metabolism as evident through increase in the activities of nitrate reductase and nitrite reductase in both the test cultivars. The positive effects of nitrogen amendments are clearly evident in the 1D protein profile studies which showed a greater accumulation of larger sub-units of RuBisCO in nitrogen amended plants. The results clearly indicate that N2 treatment effectively enhanced the yield of both the cultivars (84.8% and 76.37%, in S-151 and PUSA-N, respectively); however, the mechanistic approach adopted by the two cultivars was different. Whereas the yield quantity showed higher increments in S-151, the yield quality parameters (carbohydrates and nitrogen contents) responded more positively in PUSA-N.

Role of Elevated Ozone on Development and Metabolite Contents of Lemongrass [Cymbopogon flexuosus (Steud.) (Wats.)].

The present study was conducted to assess the effect of elevated ozone stress on the development and metabolite contents of lemongrass, a medicinal plant. The experimental plant was exposed to two elevated ozone concentrations (ambient + 15 ppb, and ambient + 30 ppb) using open-top chambers. Samplings were carried out at 45 and 90 days after transplantation (DAT), for the analysis of different characteristics, while the metabolite contents of leaves and essential oils were analyzed at 110 DAT. Both the doses of elevated ozone had notable negative effects on the carbon fixation efficiency of plants, resulting in a significant reduction in plant biomass. Enzymatic antioxidant activity increased during the second sampling, which suggests that the scavenging of reactive oxygen species was more prominent in lemongrass during the later developmental stage. The results of the present study showed a stimulated diversion of resources towards the phenylpropanoid pathway, which is made evident by the increase in the number and contents of metabolites in foliar extract and essential oils of plants grown at elevated ozone doses, as compared to ambient ozone. Elevated ozone not only upregulated the contents of medicinally important components of lemongrass, it also induced the formation of some pharmaceutically active bio compounds. On the basis of this study, it is expected that increasing ozone concentrations in near future will enhance the medicinal value of lemongrass. However, more experiments are required to validate these findings.