Growth, ultrastructural and physiological characteristics of Abelmoschus cytotypes under elevated ozone stress: a study on ploidy-specific responses.

Tropospheric ozone (O3 ) is a significant abiotic stressor whose rising concentration negatively influences plant growth. Studies related to the differential response of Abelmoschus cytotypes to elevated O3 treatment are scarce and need further exploration to recognise the role of polyploidisation in stress tolerance. In this study, we analysed the changes in growth pattern, ultrastructure, physiology and foliar protein profile occurring under O3 stress in Abelmoschus moschatus (monoploid), Abelmoschus esculentus (diploid) and Abelmoschus caillei (triploid). Our findings showed that higher stomatal conductance in A. moschatus triggered higher O3 intake, causing damage to stomatal cells and photosynthetic pigments. Additionally, it caused a reduction in photosynthetic rates, leading to reduced plant growth, total biomass and economic yield. This O3 -induced toxicity was less in diploid and triploid cytotypes of Abelmoschus . Protein profiling by sodium dodecyl sulpate-polyacrylamide gel electrophoresis showed a significant decrease in the commonly found RuBisCO larger and smaller subunits. The decrease was more prominent in monoploid compared to diploid and triploid. This study provides crucial data for research that aim to enhance plant ability to withstand O3 induced oxidative stress. Our findings may help in developing a tolerant variety through plant breeding techniques, which will be economically more advantageous in reaching the objective of sustainable production at the high O3 levels projected under a climate change scenario.

Assessment of herbaceous community structure for identifying metal-tolerant species at different land uses in and around Varanasi city.

Plant community structure under different land uses provides an important understanding of vegetation dynamics to safeguard future restoration programmes and balance ecosystem services. Therefore, this study was carried out to estimate the alterations in soil properties and contamination by potentially toxic metals at different land uses (industrial, brick kiln, highway, and residential areas) compared to the reference (botanical garden area) site coupled with their subsequent influence on herbaceous community structure, bioconcentration, translocation, and extraction amount of metals in different plant species. Most of the total and phytoavailable metals (Co, Cr, Cd, Cu, Ni, Pb, Mn, and Zn) were higher at the contaminated sites compared to the reference site. The number of herbaceous species was highest at the reference site and minimum at the industrial site. Dominant and tolerant species were Cyanodon dactylon, Croton bonaplandianus, Achyranthus aspera, Malvestrum coromendelianum, Dicanthium annulatum, Nicotiana hindostana, Sporobolus virginicus, and Parthenium hysterophorus, found at the industrial, brick kiln, and highway sites. Based on transfer coefficients, C. bonaplandianus, D. annulatum, and Eleusine indica were recognized as potential accumulators, whereas C. dactylon, Commelina benghalensis, A. aspera, Amaranthus sessilis, and M. coromendelianum were found as excluder species for different metals. The identified tolerant herbaceous species could be used for future phytoremediation strategies and the prevention of hazardous risks to living components of contaminated sites.

Effect of elevated ozone on the antioxidant response, genomic stability, DNA methylation pattern and yield in three species of Abelmoschus having different ploidy levels.

The majority of polyploids can withstand many stresses better than their monoploid counterparts; however, there is no proven mechanism that can fully explain the level of tolerance at the biochemical and molecular levels. Here, we make an effort to provide an explanation for this intriguing but perplexing issue using the antioxidant responses, genomic stability, DNA methylation pattern and yield in relation to ploidy level under the elevated level of ozone in Abelmoschus cytotypes. The outcome of this study inferred that the elevated ozone causes an increase in reactive oxygen species leading to enhanced lipid peroxidation, DNA damage and DNA de-methylation in all the Abelmoschus cytotypes. The monoploid cytotype of Abelmoschus, that is Abelmoschus moschatus L., experienced the highest oxidative stress under elevated O3, resulting in maximum DNA damage and DNA de-methylation leading to the maximum reduction in yield. While the diploid (Abelmoschus esculentus L.) and triploid (Abelmoschus caillei A. Chev.) cytotypes of Abelmoschus with lower oxidative stress result in lesser DNA damage and DNA de-methylation which ultimately leads to lower yield reduction. The result of this experiment explicitly revealed that polyploidy confers better adaptability in the case of Abelmoschus cytotypes under ozone stress. This study can further be used as a base to understand the mechanism behind the ploidy-induced stress tolerance in other plants mediated by gene dosage effect.

Ecological and health risk assessment of different land uses along with seasonal variation in toxic metal contamination around Varanasi city situated in Indo-Gangetic Plain.

Metal pollution load in soil environment has been enhanced during last few decades due to increasing industrialization and wide application of metals in all sectors. Due to the persistent and hazardous nature of metals, it can accumulate in the living system and cause severe risks to the ecosystem. The abundance of metals in soils from 5 different land use systems (industrial, industrial highway, brick kiln production area, residential highways and botanical gardens) in the Indo-Gangetic Plain region of India was analysed for three consecutive years (2018-2020) to evaluate the effects of metal load on soil properties and ecosystem health. Soil enzymatic activities, moisture, porosity, total nitrogen, and organic carbon were least at the industrial area of Ramnagar site and highest at Botanical garden area of BHU. Geochemical indices were calculated to compare the background status of metals in the soil where Cd, Cu, Cr, Co, Ni, Mn and Zn were increased in recent times. Contamination, enrichment and potential ecological risk factors with respect to Cu and Cd contents in soil were significantly higher at industrial area of Ramnagar and highway near industrial area. Maximum lifetime non-cancer and cancer health hazards were observed for Cd and Ni, respectively. The study clearly indicates that Cd, Cu and Ni are capable of posing health risk and cause imbalance in ecological functioning of soil due to chronic exposure of the potential toxic metals generated through change in land uses in sub-urban areas of Indo-Gangetic Plain region.

Photosynthetic, Biochemical and Secondary Metabolite Changes in a Medicinal Plant Chlorophytum borivillianum (Safed musli) against Low and High Doses of UV-B Radiation.

Plants are inevitably grown in presence of sunlight, therefore bound to be exposed to natural UV-B radiation. Several studies have already been conducted with UV-B and medicinal plants and only few studies showed dose dependent variation. The present study aims to find out the variations and adaptation in Chlorophytum borivillianum under two different doses of UV-B radiation; ambient + low (3.2 kJm-2 d-1 ) and high (7.2 kJm-2 d-1 ) UV-B dose, denoted as LD and HD, respectively. Reduction in photosynthetic rate was higher at HD, while plants receiving LD displayed nonsignificant variation. During vegetative and reproductive stage, significant reduction (P ≤ 0.001) in stomatal conductance was obtained when exposed to HD-eUV-B. Fv /Fm showed more reductions in HD-eUV-B (12.6%) followed by LD-eUV-B (7.9%). Low and high doses of UV-B enhanced the anthocyanin content but the increase was significant in HD, indicates epidermal protection strategy by the plants. Under LD-eUV-B, the content of saponin, a major phytochemical constituent was enhanced by 26%. Phytochemical analysis of roots revealed reduction mostly in fatty acid components whereas the steroidal components (stigmasterol and sarsasapogenin) showed enhancement in response to LD. The study suggests the importance of LD-eUV-B in the stimulation of medicinal compounds in C. borivillianum.

Individual and combined effects of chromium and ultraviolet-B radiation on defense system, ultrastructural changes, and production of secondary metabolite psoralen in a medicinal plant Psoralea corylifolia L.

The present study focuses on the effects of individual and combined stress of chromium (Cr) and ultraviolet-B (UV-B) radiation on Psoralea corylifolia L. The experiment comprised four sets: (i) control, (ii) eUV-B (elevated UV-B i.e., ambient + 7.2 kJ m-2 day-1 UV-B), (iii) Cr (chromium; 30 mg kg-1 soil), and (iv) Cr + eUV-B (chromium and elevated UV-B; Cr 30 mg kg-1 and ambient + 7.2 kJ m-2 day-1 UV-B). The eUV-B and Cr individually and in combination showed the variable responses on ultrastructure, physiology and biomass however, the impact was more prominent under individual Cr treatment followed by Cr + eUV-B and eUV-B. Higher bioconcentration factor and the lowered translocation factor consequently led to a higher reduction in the below ground biomass and the lesser reduction in above ground biomass under Cr + eUV-B treatment as compared to individual Cr treatment. In addition, higher induction in the enzymatic (glutathione reductase, ascorbate peroxidase, superoxide dismutase, and glutathione-S-transferase) and non-enzymatic antioxidants (glutathione reduced) were found to be responsible for efficient scavenging of hydrogen peroxide and superoxide radical leading to lowered MDA content under combined treatment as compared to Cr treatment. Deposition of Cr as electron dense granules in the cytoplasm, vacuoles, and cell wall under Cr and Cr + eUV-B is contemplated as one of the cellular mechanisms of P. corylifolia against the toxicity of Cr. Psoralen increased under all treatments with a maximum increase under Cr + eUV-B treatment. Taken together our results accentuated that P. corylifolia can be grown in an area contaminated with Cr and has a higher influx of UV-B for the attainment of psoralen considering its pharmaceutical perspectives.

Stabilization of metals in sludge-amended soil using red mud and its effects on yield and oil quality of Brassica juncea cultivar Kranti.

Prolonged application of sewage-sludge may cause excessive accumulation of metal(oid)s in soil, leading to phytotoxic effects. Spread of contaminants in soil can probably be hindered by using an effective metal(oid) stabilizer. Pot experiment in open field conditions was conducted for five months to evaluate the metal(oid) (Al, Cu, Zn, Cd and Cr) stabilization potential of red mud (RM) in sludge-amended soil and its effects on growth, yield, oil quality parameters and metal(oid) accumulations in Brassica juncea cultivar Kranti. The test plant was grown at different RM concentrations (0, 5, 10 and 15% w/w) in sludge-amended soil (soil/sludge: 2:1 w/w). As the total and phytoavailable metal(oid) concentrations in sludge were high, its application increased their concentrations in soil compared to the control (no RM and sludge). Increasing RM concentrations in sludge-amended soil effectively stabilized Cd followed by Cr, Cu, Zn and Al, leading to their reduced contents in plants coupled with enhanced growth performance and yield. Maximum plant (root and shoot) biomass (14.9%) and seed yield (40.4%) were found in 10% RM treatment, whereas oil content showed substantial increase with increasing RM treatments in sludge-amended soil. Mustard oil showed low rancidification, high long-chain fatty acids, saturated and polyunsaturated (ω-3 and ω-6) fatty acids within FAO ranges for edible oils under varying RM treatments compared to sludge-amended soil. Furthermore, high oleic and low erucic acid contents in mustard oil indicated a better oil quality under different RM treatments. Metal(oid) contents in seeds under different red mud treatments were within FAO/WHO limits for consumption. Thus, RM applications preferably 5 and 10% (w/w) in sludge-amended soil might be effective in stabilization of metal(oid)s using B. juncea cultivar Kranti coupled with better yield, improved oil quality and metal(oid)s within limits for human consumption.

Application potential of Chrysopogon zizanioides (L.) Roberty for the remediation of red mud-treated soil: an analysis via determining alterations in essential oil content and composition.

NOVELTY STATEMENT: The present study is of significant importance because phytoremediation of metals in red mud using essential oil-bearing plants such as Chrysopogon zizanioides (commonly known as vetiver) is a potential alternative for on-site management of the waste in most economical and sustainable way. Vetiver is a potential metal tolerant plant with high economic value; therefore the present study was accomplished to evaluate the impacts of metals in red mud on essential oil content and composition, used for remediation and stabilization of dumps. Novelty of the study is that, it aimed to utilize red mud along with sewage-sludge to cultivate vetiver which offers twin benefits, i.e. phytoremediation of metals in red mud coupled with improved quantity and quality of high valued essential oil without metal contamination.

Responses of a semi-natural grassland community of tropical region to elevated ozone: An assessment of soil dynamics and biomass accumulation.

Despite knowing the phytotoxic effects of tropospheric ozone (O3), which is of global concern, there is no study so far reported about its impacts on grassland community of tropical regions. Therefore, we assessed the responses of a semi-natural grassland community of Indo-Gangetic plains to elevated O3 exposure (Ambient + 20 ppb) compared to ambient after three years of exposure using open-top chambers. Percent decreases were found in above (26%; p ≤ 0.002) and belowground (30%; p ≤ 0.003) biomass under elevated compared to ambient O3 exposure. Percent decrements in total organic carbon (TOC; 24%; p ≤ 0.001), total nitrogen (29%; p ≤ 0.001) and available phosphorus (11%; p ≤ 0.002) in the soil were also observed under elevated O3 exposure. Exposure at elevated O3 reduced soil microbial biomass and activities of ß-glucosidase, amylase, urease and phosphatase, while polyphenol oxidase and peroxidase showed enhancement in their activities, showing negative effects on belowground soil health. Percent reduction in root shoot ratio (10%; p ≤ 0.05) depicts that less C-allocation towards root system led to a reduction in TOC in the soil, which could affect C-sequestration under elevated O3 condition in the semi-natural grasslands. Elevated O3 also affected enzymes participating in N and P-cycles, causing reductions in total nitrogen and phosphorus. The study concludes that projected O3 concentrations have serious implications for aboveground biomass as well as belowground soil health in tropical areas, identified as hotspots of O3 in the world.

Role of supplemental UV-B in changing the level of ozone toxicity in two cultivars of sunflower: growth, seed yield and oil quality.

Ultraviolet-B radiation (UV-B) is inherent part of solar spectrum and tropospheric ozone (O3) is a potent secondary air pollutant. Therefore the present study was conducted to evaluate the responses of Helianthus annuus L. cvs DRSF 108 and Sungold (sunflower) to supplemental UV-B (sUV-B; ambient + 7.2 kJ m-2 d-1) and elevated ozone (O3; ambient + 10 ppb), given singly and in combination under field conditions using open-top chambers. The individual and interactive effects of O3 and sUV-B induced varying changes in both the cultivars of sunflower ranging from ultrastructural variations to growth, biomass, yield and oil composition. Reduction in leaf area of Sungold acted as a protective feature which minimized the perception of sUV-B as well as uptake of O3 thus led to lesser carbon loss compared to DRSF 108. Number- and weight of heads plant-1 decreased although more in Sungold with decline of oil content. Both the stresses when given singly and combination induced rancidification of oil and thus made the oil less suitable for human consumption.

Heteropogon contortus BL-1 (Pilli Grass) and Elevated UV-B Radiation: The Role of Growth, Physiological, and Biochemical Traits in Determining Forage Productivity and Quality.

Exposure to elevated UV-B (eUV-B) is well known for its phytotoxicity, although studies made with UV-B exposure and its impact on grasses are limited especially from tropical countries including India. In this study, responses of a valuable grass species, Heteropogon contortus BL-1, were assessed under eUV-B (over ambient UV-B) at different growth stages. Damage caused by eUV-B was observed in the form of membrane damage and loss of pigments at early stages of growth, whereas tannin, phenol, and protein contents showed their increments at all the growth stages, to overcome the imposed stress. Reducing sugar showed its decline at all the growth stages, whereas starch and sucrose contents were higher mostly at later ages of plant growth. eUV-B caused a marked variations in anatomical structures with increase of mesophyll and spongy parenchymatous cells in leaves to reduce severity of irradiation, to maintain the growth and productivity. The study also highlights the significant negative influence of eUV-B on the growth of H. contortus BL-1 and its adaptive strategy to minimize the negative impacts. With the progression of age, plants although adopted to UV-B stress with maintenance of productivity, but palatability of forage was affected due to increment of tannin content.

The influence of urban stress factors on responses of ground cover vegetation.

A comprehensive study was conducted to evaluate the effects of ambient air pollution, land use, and soil properties on ground cover vegetation in the urban area of Varanasi city, situated in the Indo Gangetic Plain of India. Twelve leaf functional traits were assessed on eight most dominant herbaceous species belonging to four angiospermic families in three different land uses with varying air pollution loads and soil properties. Particulate matter (PM10 and TSP), gaseous pollutants (SO2, NO2, and O3), land uses (built-up area, shrub, and grass cover), and soil properties showed significant variability among the land uses. Air pollution was identified as the major stress factor which influenced leaf functional traits of ground cover vegetation followed by soil properties and land uses. Among the plants, Croton sparsiflorus was found to be the most responsive plants to all the factors. Plants responded differently under varying environmental factors as Euphorbia hirta was maximally influenced by air pollution, whereas the effect of land use was maximum in C. sparsiflorus. Influence of soil properties was highest in Digitaria ciliaris and Scoparia dulcis. All the environmental factors in combination maximally influenced non-enzymatic antioxidants (ascorbic acid and polyphenolics) followed by photosynthetic pigments among the different leaf functional traits. Among the environmental factors, NO2 and PM were identified as the most influencing factors regulating leaf functional traits followed by K level in soil and shrub cover. It can be concluded that responses of different leaf functional traits of ground cover vegetation varied with different environmental factors and responses were mostly species specific.

Effect of elevated ozone and varying levels of soil nitrogen in two wheat (Triticum aestivum L.) cultivars: Growth, gas-exchange, antioxidant status, grain yield and quality.

Tropospheric ozone (O3) is a phytotoxic air pollutant causing a substantial damage to plants and agriculture worldwide. Plant productivity is affected by several environmental factors, which interact with each other. Studies related to interactions involving O3 and different levels of nitrogen (N) are still rare and elusive. In the present study we grew two wheat cultivars (HD2967 and Sonalika) in open top chambers (OTC) under ambient (AO) and elevated O3 (EO) (ambient + 20 ppb O3) and provided two levels of N fertilization; (a) recommended nitrogen (RN), (b) 1.5 times the recommended N (HN). Growth (root/shoot ratio, leaf number and leaf area), biomass, gas-exchange (stomatal conductance (gs), photosynthesis (A), transpiration (E), chlorophyll fluorescence (Fv/Fm), physiological (chlorophyll and carotenoids), biochemical [antioxidant activity, lipid peroxidation (MDA)] parameters and leaf N content were measured at the vegetative and reproductive phases. Yield attributes (spike weight plant-1, grain weight plant-1, grain numbers plant-1, husk weight plant-1, straw weight plant-1, 1000 grain weight, harvest index) and seed N content were analyzed at the final harvest stage. Grain yield plant-1 was decreased in Sonalika under EO irrespective of different levels of N fertilization. Seed N content decreased by 3.9% and 5.6% in HD2967 and Sonalika, respectively, under EO at RN treatment. Antioxidant defense played an important role in protecting the plants against O3 stress which was enhanced under HN treatment. Response of antioxidants varied between the cultivar, growth phase (at the vegetative or reproductive phase) and the N levels (RN or HN). Cultivar HD2967 was characterized by higher biomass, gs and stronger antioxidant protection system, while, Sonalika showed early senescence response (decreased leaf number plant-1, gs) and greater resources allocation towards eco-physiological parameters (increased A and Fv/Fm) at the vegetative phase, resulting in the significant decrease in the yield attributes. Further study warrants the need to screen a large number of cultivars in relation to their response to various levels of N fertilization to minimize the yield losses under highly O3 polluted areas.

A Global Perspective of Fine Particulate Matter Pollution and Its Health Effects.

Fine particulate matter (PM) in the ambient air is implicated in a variety of human health issues throughout the globe. Regulation of fine PM in the atmosphere requires information on the dimension of the problem with respect to variations in concentrations and sources. To understand the current status of fine particles in the atmosphere and their potential harmful health effects in different regions of the world this review article was prepared based on peer-reviewed scientific papers, scientific reports, and database from government organizations published after the year 2000 to evaluate the global scenario of the PM2.5 (particles <2.5 µm in aerodynamic diameter), its exceedance of national and international standards, sources, mechanism of toxicity, and harmful health effects of PM2.5 and its components. PM2.5 levels and exceedances of national and international standards were several times higher in Asian countries, while levels in Europe and USA were mostly well below the respective standards. Vehicular traffic has a significant influence on PM2.5 levels in urban areas; followed by combustion activities (biomass, industrial, and waste burning) and road dust. In urban atmosphere, fine particles are mostly associated with different health effects with old aged people, pregnant women, and more so children being the most susceptible ones. Fine PM chemical constituents severely effect health due to their carcinogenic or mutagenic nature. Most of the research indicated an exceedance of fine PM level of the standards with a diverse array of health effects based on PM2.5 chemical constituents. Emission reduction policies with epidemiological studies are needed to understand the benefits of sustainable control measures for fine PM mitigation.

Influence of metals on essential oil content and composition of lemongrass (Cymbopogon citratus (D.C.) Stapf.) grown under different levels of red mud in sewage sludge amended soil.

Lemongrass is a commercially important perennial herb with medicinal value and ability to tolerate high alkaline and saline conditions. Essential oil bearing plants can grow safely in soil contaminated with heavy metals without severe effects on morphology and oil yield. The present study was aimed to assess the essential oil content and composition in lemongrass in response to elevated metals in above-ground plant parts. Pot experiment was conducted for six months using sewage sludge as soil amendment (soil: sludge: 2:1 w/w) followed by red mud treatments (0, 5, 10 and 15% w/w). Garden soil without sludge and red mud was control and there were ten replicates of each treatment. Oil content in leaves was differently affected due to presence of metals in soil under different treatments. Oil content under SRM5 (5% red mud) treatment was raised by 42.9 and 11.5% compared to the control and SRM0 treatment, respectively. Among identified compounds in oil under red mud treatments, 17 compounds contributed more than 90% of total volatiles (citral contributing approximately 70%). Under SRM10 treatment, essential oil showed maximum citral content (75.3%). Contents of Fe, Zn, Cu, Cd, Ni and Pb in above-ground plant parts exceeded, whereas Mn was detected within WHO permissible limits for medicinal plants. However, metal contents in essential oil were well within FSSAI limits for food. The study suggests utilization of 5 and 10% red mud in sludge amended soil for lemongrass cultivation to have better oil yield and quality, without metal contamination.

Assessment of ethylene diurea-induced protection in plants against ozone phytotoxicity.

Urbanization, industrialization and unsustainable utilization of natural resources have made tropospheric ozone (03) one of the world's most significant air pollutants. Past studies reveal that 0 3 is a phytotoxic air pollutant that causes or enhances food insecurity across the globe. Plant sensitivity, tolerance and resistance to 0 3 involve a wide array of responses that range from growth to the physiological, biochemical and molecular. Although plants have an array of defense systems to combat oxidative stress from 0 3 exposure, they still suffer sizable yield reductions. In recent years, the ground-level 0 3 concentrations to which crop plants have been exposed have caused yield loses that are economically damaging. Several types of chemicals have been applied or used to mitigate the effects produced by 0 3 on plants. These include agrochemicals (fungicides, insecticides, plant growth regulators), natural antioxidants, and others. Such treatments have been effective to one degree to another, in ameliorating Or generated stress in plants. Ethylene diurea (EDU) has been the most effective protectant used and has also served as a monitoring agent for assessing plant yield losses from 0 3 exposure. In this review, we summarize the data on how EDU has been used, the treatment methods tested, and application doses found to be both protective and toxic in plants. We have also summarized data that address the nature and modes of action (biophysical and biochemical) of EDU. In general, the literature discloses that EDU is effective in reducing ozone damage to plants, and indicates that EDU should be more widely used on 0 3 sensitive plants as a tool for biomonitoring of 0 3 concentrations. Biomonitoring studies that utilize EDU are very useful for rural and remote areas and in developing countries where 0 3 monitoring is constrained from unavailability of electricity. The mechanism(s) by which EDU prevents 0 3 toxicity in plants is still not completely known. EDU possesses great utility for screening plant sensitivity under field conditions in areas that experience high 0 3 concentrations, because EDU prevents 0 3 toxicity only in 0 3 sensitive plants. Ozone-resistant plants do not respond positively to EDU applications. However, EDU application dose and frequency must be standardized before it can be effectively and widely used for screening 0 3 sensitivity in plants. EDU acts primarily by enhancing biochemical plant defense and delaying Or induced senescence, thereby reducing chlorophyll loss, and maintaining physiological efficiency and primary metabolites; these actions enhance growth, biomass and yield of plants. We believe that future studies are needed to better address the EDU dose response relationship for many plant species, and to screen for new cultivars that can resist 0 3 stress. Although some research on the physiological and biochemical mechanisms of action of EDU have been performed, the new 'omics' tools have not been utilized to evaluate EDUs mechanism of action. Such data are needed, as is gene expression and proteome profiling studies on EDU-treated and -untreated plants.

Application of ethylene diurea (EDU) in assessing the response of a tropical soybean cultivar to ambient O3: nitrogen metabolism, antioxidants, reproductive development and yield.

The present study deals with assessment of response of a tropical soybean cultivar to O3 in relation to photosynthetic pigments, chlorophyll fluorescence kinetics, antioxidative capacity, N assimilation enzymes, metabolites, growth and yield using ethylene diurea (EDU) given as a soil drench (400) ppm at an interval of 10 days after germination up to maturity. Mean O3 concentration was 42 ppb and accumulated threshold above 40 ppb (AOT 40) was 9.07 ppm h. Lipid peroxidation and total phenolics reduced, while increases in activities of antioxidative and nitrogen assimilation enzymes, ascorbic acid, protein, photosynthetic pigments, Fv/Fm ratio, number of leaves, flowers, pods, branches and yield attributes were found in EDU treated plants. EDU alleviated the negative effects of O3 by enhancing the first line of defense against ROS and protecting N assimilation enzymes at flowering and maintaining adequate supply of photosynthates to developing pods during pod filling stage. EDU provided maximum protection between flowering to pod filling stage.

Responses of pea plants to elevated UV-B radiation at varying nutrient levels: N-metabolism, carbohydrate pool, total phenolics and yield.

The effects of elevated UV-B (280-315nm) were assessed on nitrogen metabolism, carbohydrate pool, total phenolics, photosynthetic pigments, UV-B absorbing compounds, variables related to oxidative stress, biomass and yield of pea plants grown under various levels of NPK. The NPK levels assayed were: background NPK level (F0); recommended NPK (F1) and recommended NK+1.5×recommended P (F2) and the UV-B levels were: control (C) and elevated (T). The responses of T plants varied with different combinations of NPK. Yield reduced under elevated UV-B at all NPK levels with maximum reduction in F0T and minimum reduction in F1T. Leghaemoglobin content was reduced under elevated UV-B at all NPK levels. Maximum increase in malondialdehyde content recorded in F0T plants corresponded with higher superoxide and hydrogen peroxide contents. Nitrite reductase activity decreased significantly under UV-B at all NPK levels, but nitrate reductase activity increased significantly in F1T and F2T. Maximum reduction in C:N ratio of leaves in F2T plants suggests competition between sucrose synthesis and nitrate reduction under additional P level. The study concludes that application of recommended level of NPK caused least changes in N metabolism leading to minimum yield losses due to elevated UV-B stress.

UVR8 mediated plant protective responses under low UV-B radiation leading to photosynthetic acclimation.

The UV-B photoreceptor UVR8 regulates the expression of several genes leading to acclimation responses in plants. Direct role of UVR8 in maintaining the photosynthesis is not defined but it is known to increase the expression of some chloroplastic proteins like SIG5 and ELIP. It provides indirect protection to photosynthesis by regulating the synthesis of secondary metabolites and photomorphogenesis. Signaling cascades controlled by UVR8 mediate many protective responses thus promotes plant acclimation against stress and secures its survival.

Differential sensitivity of spinach and amaranthus to enhanced UV-B at varying soil nutrient levels: association with gas exchange, UV-B-absorbing compounds and membrane damage.

The metabolic reasons associated with differential sensitivity of C3 and C4 plant species to enhanced UV-B under varying soil nutrient levels are not well understood. In the present study, spinach (Spinacia oleracea L. var All Green), a C3 and amaranthus (Amaranthus tricolor L. var Pusa Badi Chaulai), a C4 plant were subjected to enhanced UV-B (280-315 nm; 7.2 kJ m(-2) day(-1)) over ambient under varying soil nutrient levels. The nutrient amendments were recommended Nitrogen (N), Phosphorus (P), Potassium (K), 1.5× recommended NPK, 1.5× recommended N and 1.5× recommended K. Enhanced UV-B negatively affected both the species at all nutrient levels, but the reductions varied with nutrient concentration and combinations. Reductions in photosynthetic rate, stomatal conductance and chlorophyll content were significantly more in spinach compared with amaranthus. The reduction in photosynthetic rate was maximum at 1.5× recommended K and minimum in 1.5× NPK amended plants. The oxidative damage to membranes measured in terms of malondialdehyde content was significantly higher in spinach compared with amaranthus. Enhanced UV-B reduced SOD activity in both the plants except in amaranthus at 1.5× recommended K. POX activity increased under enhanced UV-B at all nutrient levels in amaranthus, but only at 1.5× K in spinach. Amaranthus had significantly higher UV-B-absorbing compounds than spinach even under UV-B stress. Lowest reductions in yield and total biomass under enhanced UV-B compared with ambient were observed in amaranthus grown at 1.5× recommended NPK. Enhanced UV-B did not significantly change the nitrogen use efficiency in amaranthus at all NPK levels, but reduced in spinach except at 1.5× K. These findings suggest that the differential sensitivity of the test species under enhanced UV-B at varying nutrient levels is due to varying antioxidative and UV-B screening capacity, and their ability to utilize nutrients. Amaranthus tolerated enhanced UV-B stress more than spinach at all nutrient levels and 1.5× recommended NPK lowered the sensitivity maximally to enhanced UV-B with respect to photosynthesis, biomass and yield. PCA score has also confirmed the lower sensitivity of amaranthus compared with spinach with respect to the measured physiological and biochemical parameters.