Aditya Abha Singh

Cultivar specific variations in antioxidative defense system, genome and proteome of two tropical rice cultivars against ambient and elevated ozone

For the past few decades continuous increase in the levels of tropospheric ozone (O3) concentrations is posing to be a threat for agricultural productivity. Two high yielding tropical rice cultivars (Malviya dhan 36 and Shivani) were evaluated against different concentrations of O3 under field conditions. Experimental design included filtered chambers, non-filtered chambers having ambient O3 and 10 and 20ppb elevated O3 above the ambient. Study was conducted to assess differential response if any in induction of antioxidative defense system, genome stability, leaf proteome, yield and quality of the product in both the test cultivars. Superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) were induced under ambient and elevated levels of O3. Native polyacrylamide gel electrophoresis (PAGE) of SOD, CAT and POD also displayed increased enzymatic activity along with associated alterations in specific isoforms. Ascorbic acid, thiols and phenolics were also stimulated at ambient and elevated O3. Structural alterations in DNA of rice plants due to O3 affecting its genome template stability (GTS) was examined using RAPD technique. 2-D PAGE revealed 25 differential spots in Malviya dhan 36 and 36 spots in Shivani after O3 treatment with reductions in RuBisCO subunits. Reductions in yield and change in the quality of grains were also noticed.

Tropospheric ozone pollution in India: effects on crop yield and product quality

Ozone (O3) in troposphere is the most critical secondary air pollutant, and being phytotoxic causes substantial losses to agricultural productivity. Its increasing concentration in India particularly in Indo-Gangetic plains is an issue of major concern as it is posing a threat to agriculture. In view of the issue of rising surface level of O3 in India, the aim of this compilation is to present the past and the prevailing concentrations of O3 and its important precursor (oxides of nitrogen) over the Indian region. The resulting magnitude of reductions in crop productivity as well as alteration in the quality of the product attributable to tropospheric O3 has also been taken up. Studies in relation to yield measurements have been conducted predominantly in open top chambers (OTCs) and also assessed by using antiozonant ethylene diurea (EDU). There is a substantial spatial difference in O3 distribution at different places displaying variable O3 concentrations due to seasonal and geographical variations. This review further recognizes the major information lacuna and also highlights future perspectives to get the grips with rising trend of ground level O3 pollution and also to formulate the policies to check the emissions of O3 precursors in India.

Effect of elevated O3 on rhizospheric enzymatic activities of ozone sensitive and tolerant wheat cultivars

ABSTRACT Tropospheric ozone (O3) is considered harmful to agriculture production and soil community. Wheat cultivars HD 2987 (O3 sensitive) and Kharchiya 65 (O3 tolerant) were grown under ambient and elevated (ambient + 30 ppb) levels of O3 (EO) using open top chambers, and microbial biomass and enzymatic activities were investigated in soil rhizosphere. Elevated O3 declined soil enzymatic activities related to carbon cycling viz. β-glucosidase, cellobiohydrolase, cellulase and amylase more in sensitive cultivar compared to tolerant. Enzymatic activities linked to nitrogen cycling like N-acetyl-glucosaminidase and urease decreased while protease and glycine aminopeptidase increased. Microbial biomass carbon and nitrogen declined more in sensitive cultivar by 11.1 and 21.2%, respectively. Root biomass reduced in wheat cultivars with an increase of their phenolics contents by 34.3 and 10.2% in HD 2987 and Kharchiya 65, respectively at 60 days after germination. Non-significant changes were observed in soil organic carbon and total nitrogen in both the cultivars. Redundancy analysis suggested that soil enzymatic activities were predominantly affected by O3 induced changes in microbial biomass carbon and root biomass. Study also showed that rhizosphere of sensitive cultivar HD 2987 was affected more under EO as compared to tolerant Kharchiya 65.

Ozone Toxicity and Remediation in Crop Plants

Tropospheric ozone (O3) phytotoxicity is a major threat to agricultural production leading to global yield loss of about 3.9–15% for wheat, 8.5–14% for soybean and 2.2–5.5% for maize. At a global scale, the United States displays a decline in O3 level of about 17% from 2000–2015. O3 concentration in the United States is about two times higher than that of Europe. Despite the declining trend in these two continents, the prevailing concentrations are still high enough to affect the plant growth and productivity. Beside this, a significant rise in O3 pollution is observed in various Asian countries. China, the fastest developing nation of Asia, has shown an increase of surface O3 concentration by 0.58 ppbv/yr. from 1994 to 2007. A continuous increase in the emission of O3 precursors in southern and central Asia has been reported due to weaker legislative policies in the developing countries, contributing to more O3 prevalence in such regions. A simulation study projected an increase of global tropospheric O3 by 4.3 ± 2.2 ppb with maximum increment displayed in South Asia, South-East Asia and Middle Eastern region.

Tropospheric O3: A Cause of Concern for Terrestrial Plants

Tropospheric ozone (O3) is a phytotoxic pollutant causing risk to food production, pasture, and forest communities. In the present scenario, unsustainable resource utilization has turned this secondary pollutant into a major component of global climate change. The background levels of O3 are very high, and IPCC projections have shown that it will increase by 20–25 % in 2050 and 40–60 % in 2100, causing severe consequence on global food security. Ozone enters plants through stomata, where it can be dissolved in the apoplastic fluid. Ozone has several potential effects on plants: direct reaction with cell membranes, generation of ROS and H2O2 (which alter cellular function by causing cell death), induction of premature senescence, negative impact on photosynthetic machinery and up- or downregulation of antioxidants, defense reactions, and variations in metabolic pathways. Tropospheric O3 causes changes in tree diameter, wood quality, herbivory pattern, forage quality, and crop yield and quality. In this chapter, we make an attempt to present an overview of O3 concentrations throughout the globe and its impact on agricultural crops, forest, and grassland ecosystems. We summarized the information available on plant responses to O3 at physiological, cellular, and biochemical levels; crop yield; and forest and grassland communities at present concentrations and also under projected future concentrations.