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Research Article Open Access

Susceptibility of Some Wheat (Triticum aestivum L.) Varieties to Aerosols of Oxidised and Reduced Nitrogen

Bhagawan Bharali1*, Bhupendra Haloi1, Jayashree Chutia1, Sonbeer Chack1and Koilash Hazarika2
1Department of Crop physiology, Faculty of Agriculture, AAU, Jorhat, Assam, India
2Instruction-Cum-Research Farm, AAU, Jorhat, India
Corresponding Author : Bhagawan Bharali
Department of Crop physiology Faculty of Agriculture
AAU, Jorhat, Assam, India
Tel:+919957179617
Fax: +91 376 2310183
E-mail: bbharali33@rocketmail.com; bbharali@aau.ac.in
Received: February 20, 2015 Accepted: August 07, 2015 Published:August 13, 2015
Citation: Bharali B, Haloi B, Chutia J, Chack S, Hazarika K (2015) Susceptibility of Some Wheat (Triticum aestivum L.) Varieties to Aerosols of Oxidised and Reduced Nitrogen. Adv Crop Sci Tech 3:182. doi:10.4172/2329-8863.1000182
Copyright: © 2015 Bharali B, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Abstract

In a pot culture (2011), aerosols of oxidized nitrogen (NaNO2) @20 kgha-1 yr-1 (≈200 ppm), reduced nitrogen (NH4Cl) @10 kg-1 hayr-1 (≈100 ppm) and distilled water (control) were sprayed (1500 cm3 plant-1 of each solution) weekly at different days after sowing (DAS) to study their impacts on physiology of wheat varieties (Ankur Omkar, Sonalika and K-306). In a field trial (2012), the simulated N-aerosols @ 200 ppm and 400 ppm (1000 cm3 m-2 for each solution) along with a control were sprayed to population of the best variety (Ankur Omkar) at four different growth stages. In both pot and field experiments foliar feeding of aerosols with lower dose at the earlier growth stages influenced nitrogen use efficiency and yield. Fluctuations of cellular cations (Ca2+, K+) or peroxidase activity were caused by the aerosols and altered membrane permeability.

Keywords
Cations; Nitrogen use efficiency; Nitrate reductase; Net photosynthesis; Peroxidase; Membrane permeability
Abbreviations
NaNO2: Sodium Nitrite; NH4Cl: Ammonium Chloride; NUE: Nitrogen Use Efficiency; NR: Nitrite Reductase; CMS: Cell Membrane Stability; DAS: Days after sowing; CRI: Crown Root Initiation; Pn: Net Photosynthesis; d.w: Dry Weight
Introduction
Nitrogen oxides (NO, NO2 and N2O or NOx) are recognized as atmospheric pollutants in rapidly growing urban and peri-urban areas of Northeast India [1]. Nitrogen dioxide gets dissolved in the extra-cellular water, form HNO2 and HNO3, which then dissociate to nitrate, nitrite and protons [2]. Reduced nitrogen incorporates into a wide range of compounds in nearly all higher plants [3]. Higher concentration (<10 μll-1) of oxides of nitrogen alter the physiological processes including net photosynthesis and yields [4].
Reduced nitrogen (gaseous NH3 or particulate NH+4 called NHy) causes acidification of the ecosystem [5,6]. NHy contributes to a substantial portion of total deposition of nitrogen [7]. Ammonia at high concentration (>1 mM) is toxic to plants [8]. The consequences of high N deposition are seen in terrestrial ecosystem [9]. Foliar feeding of plants with aerosols of oxidised (NaNO2) and reduced nitrogen (NH4Cl) might affect growth stages and yield attributes of wheat varieties. We examined dose responses of wheat crop to N-aerosols and discussed mechanism(s) for varietal susceptibility or tolerance to the aerosols.
Materials and Methods
Cultural practices
Three wheat cultivars viz., K-306, Sonalika and Ankur Omkar were included in the pot experiments. A mixture (5 g) of urea, super phosphate and muriate of potash @2:1:1 were added to acid mineral soil in pots (size 5 kg) before raising plants from the seeds. In field, these fertilizers @ 80:46:42 per hectare were applied as basal before sowing of wheat seeds (variety: Ankur Omkar). The crop was irrigated during the growth periods to avoid desiccation. The experiments were laid in Randomized Block Design and replicated thrice.
Application of aerosols
In pot experiment 100 ppm NH4Cl and 200 ppm NaNO2 were sprayed on foliage at four growth stages viz., 0-30 DAS: germination cum crown root initiation (CRI); 30-60 DAS: tillering; 60-90 DAS: maximum tillering; and 90-120 DAS: reproductive development. Total volume of the each solution was 1500 cm3 per stage. Similarly, solutions (1000 cm3 per stage) each of 200 ppm NH4Cl and 200 ppm NaNO2 and distilled water (control) were sprayed to population of wheat crop at the four different growth stages. Drifting of the solutions from one pot or plot to another was prevented by using a hard board at the time of spray.
Measurement of net photosynthesis
We used transparent, airtight acrylic assimilation chambers (60 x 60 x 60 cm3 for pot plants and 15 x 15 x 15 cm3 field samples). Temperature (27-29°C), Relative humidity (52-57%) and Light intensity (23-27 Klux) inside the assimilation chambers were recorded by Hygrometer and Light meter respectively. The pot plants or leaf samples from field were incubated in presence of ambient 380 ppm CO2 in sunlight during mid-day for half an hour. Inside air sample (10 cm3) was collected by clinical syringe through the rubber port of the chambers, and injected into Environmental Gas Monitor (EGM-4) for measuring carbon dioxide concentration after incubation of plants inside the assimilation chamber. The rate of net photosynthesis was expressed as ppm CO2 absorbed g-1 plant Dw h-1 [10].
NR activity in plants
Nitrate reductase activity was estimated based on conversion of nitrate to nitrite and inhibition of nitrite reduction to ammonia in anaerobic condition [11]. Green leaf samples (0.03 g) of 10-15 mm2 size were put into 2.5 ml solution containing 200 mM phosphate buffer (pH 7.5), 30 mM KNO3, 5% (v/v) propanol in assay tubes. The tubes were incubated in a water bath at 30°C for 30 minutes, at 100°C for 2 minutes and allowed them to cool to room temperature. To detect nitrite, 1 ml each of 1% sulfanilamide in 1N HCl and 0.02% N-(1-naphthyl)-ethylene diamine dihydrochloride were added to the solution. The solution was mixed thoroughly and kept in dark at room temperature for 15 min. Then, absorbency readings measured at 540 nm by spectrophotometer were plotted on a standard curve, which was prepared from a stock of 25 nmol nitrite per ml using KNO2 in water.
Peroxidase activity in plants
Lipid peroxidation was measured in terms of Malondialdehyde content (MDA) [12]. Leaf sample (0.5 g) was homogenized in 10 ml of 0.1 per cent trichloroacetic acid. The homogenate was centrifused at 15,000 g for 5 minutes. The aliquot (2 ml) of the supernatant and 4 ml of 0.5% thiobarbuteric acid (TBA) in 20 per cent of TCA were mixed. The mixture was heated at 95°C for 30 minutes and cooled in ice bath. It was centrifused at 10,000 g for 5 minutes and the absorbance of supernatant was recorded at 532 nm. The value for non-specific absorption at 600 nm was subtracted from the value of 532 nm. The absorption coefficient of 155 nmol per cm was used to calculate MDA content as: MDA (nmol per g fresh weight) = (OD x 6)/0.155 x volume extract / (2 x weight of sample)
Nitrogen use efficiency (NUE) of crop
Kjeldhal method was used to determine total Nitrogen content, which is based on catalytic conversion of organic nitrogen into ammonia and its subsequent estimation by acid base titration [13]. NUE in grains of wheat varieties under treatments were calculated from their per cent Nitrogen and dry weight as: NUE% in grain = (Nitrogen % in grain x total grain yield per plant or per plot.
Measurement of CMS and estimation of cations
Cell Membrane permeability was measured in terms of CMS [14]. Twenty pieces of young leaves from the treated plants were cut into size of one centimeter square and immersed them first into 20 cm3 distilled water in plastic bottles of 60 cm3 capacity. The bottles were closed tightly to avoid leaking of the solution and checked gently using magnetic stirrer. Thus, freely water soluble ions in intercellular spaces of leaf were removed by the three serial washes with distilled water (each 10 min, 20 cm3). Then, to extract the cations present in the exchangeable sites of the cellular locations, the same leaf discs were eluted by two treatments (each 1 h 20 cm3) with 25 mM Sr2Cl [15]. The solutions were collected into other plastic bottles. The plant samples were oven dried at 60°C to a constant weigh. The electrical conductivity readings of these solutions against the samples collected from the experimental treatments were used to compute CMS as follows.
CMS = [1-(1-T1/T2)/(1-C1/C2) × 100]/ Dry weight of leaf samplesWhere,
Where,
T1= Conductivity reading of 25 mM Sr2Cl (20 cm3) without leaf samples
T2= Conductivity readings of 25 mM Sr2Cl (20 cm3) with leaf samples
C1= Conductivity reading of double distilled water without leaf samples
C2= Conductivity readings of double distilled water with leaf
Intercellular and exchangeable Cations (K+ and Ca2+) extracted by distilled water and 25 mM Sr2Cl respectively, were estimated using a Thermo Jarrel Ash S12 atomic absorption/emission spectrophotometer (Franklin, MA, USA) and air-acetylene mixture. Element contents of the leaves were expressed in terms of their oven dry weight.
Economic yield
Grains were threshed out from the plants under respective treatments at different growth stages of wheat crop and expressed as gram per plant (in case of pot plants) and quintal per hectare in field harvest.
Statistical analysis
Data were analysed following Generalised Linear Model (GLIM) program of Royal Society of London. Significant differences between two mean values due to treatments or varieties and their interaction at a crop growth stage were computed by comparing their significant levels at P<0.05.
Results
Net photosynthesis
In the pot experiment (Table 1), Pn at the germination-cum CRI stage of the crop (i.e.0-30DAS) varied significantly among the varieties. The variety Ankur Omkar had the highest Pn followed by Sonalika>K-306. In general, NH4Cl lessened and NaNO2 increased Pn by about 1% and 7.89% respectively. The Pn differed significantly due to treatments at tillering stage (i.e. 30-60 DAS) of the crop. There were 16.71% and 29.52% reductions of Pn NH4Cl and NaNO2 respectively. Variety Ankur Omkar had the highest Pn followed by K-306>Sonalika. Both varieties and treatments had significant effects on Pn at the maximum tillering stage i.e. 60-90 DAS. Variety K-306 showed the highest Pn followed by Sonalika> Ankur Omkar at this stage. NH4Cl and NaNO2 brought down Pn by 9.89% and 15.704% respectively as compared to the control. The varieties had significant differences in respect of Pn at the reproductive development stage i.e. 90-120 DAS of the crop only. The order of Pn in varieties was K-306>AnkurOmkar>Sonalika.
In the field experiment (Figure 1), the treatments brought about significant changes in Pn of the wheat crop. Plants treated with the oxidised and reduced nitrogen had lower Pn by 5-6.5% only as compared to control. However, there were higher variations in Pn with respect to crop stages. The Pn declined at the later growth stages with application of the aerosols (Stage 1 (20.58%)>Stage 2 (46.82%)>Stage 3 (15.33%)>Stage 4). It may be due to the negative impact of the aerosols at the later growth stages as compared to the earlier ones.
Nitrate reductase activity activity
In the pot experiment (Table 2), both varieties and treatments had significant effects on NR activity of wheat crop. The effects of NH4Cl on NR of varieties were negligible, whereas NaNO2 increased NR activity merely (by 6.48%) as compared to control. Variety Ankur Omkar possessed the highest NR followed by Sonalika>K-306. At the maximum tillering stage, NR activity was significantly affected by variety and treatments. Variety Ankur Omkar had the highest NR followed by Sonalika > K-306. NH4Cl enhanced NR activity by 34.07% and NaNO2 by 7.69% as compared to control. Neither the variety nor the treatments at reproductive development stage exhibited significant changes in NR activity.
In the field experiment (Figure 2), NR activity varied significantly due to the treatments with respect to time of application. Leaves treated with aerosols had lower NR activity. There were decreases in NR activity by NaNO2 (21.62% and 28.0%) than by NH4Cl (19.39%, 11.26%) at 200 and 400 ppm respectively. Also, lower NR activity was found with the higher doses of the aerosols.
Nitrogen use efficiency
Data on NUE in wheat grains from the pot experiment are presented in Table 3. In this experiment, there were 1.87% and 8.88% reductions of grain NUE in NH4Cl and NaNO2 treated plants respectively. Some differences in NUE were found among the varieties, where Sonalika>Ankur Omkar>K-306. The variety and treatments had significant effects on grain NUE at maximum tillering stage of the crop.
There were 16.1% and 19.1% increases in grain NUE by NH4Cl and NaNO2 respectively. Variety Ankur Omkar ranked first followed by Sonalika > K-306 in case of grain NUE. The N aerosols had significant effects on the grain NUE at reproductive development stage of the crop. There were 21.99% and 27.03% increases in grain NUE by NH4Cl and NaNO2 respectively. The variety Ankur Omkar had higher grain NUE than K306>Sonalka varieties.
In the field experiment, NUE (Figure 3) increased in leaf at 400 ppm NH4Cl as well as 200 ppm and 400 ppm NaNO2 treatments (by 25.47%, 26.17% and 4.38% respectively). NUE fluctuates at different days after sowing (Stage 2 (18.84) % >Stage 4(17.27%)>Stage 3 (9.68%)>Stage 1).
Cell membrane stability
In the pot experiment (Table 4), CMS was affected significantly by the treatments at tillering stage of wheat crop. Variety Ankur Omkar>K-306>Sonalika had differences in CMS. Both varieties and treatments had significant effects on CMS of wheat crop at maximum tillering stage. K-306>Ankur Omkar>Sonalika had a variable CMS. On an average, N-aerosols applied at the reproductive development stage, had significant effects on CMS of Wheat crop. Ammonium chloride and Sodium nitrite increased CMS up-to 46.62% and 84.46% respectively as compared to control. The varieties Sonalika>Ankur Omkar>K-306 had some differences in their CMS.
In the field experiment (Figure 4), Cell membrane stability of wheat did not differ significantly for the treatments. However, a higher CMS was found in early application of the aerosols than at the later stage (Stage 1>Stage 2>Stage 4>Stage 3 by 1.22%, 13.63%, 5.36% respectively).
Economic yield
In the pot experiment, economic yield of wheat varieties corresponding to the treatments are presented in Table 5. N-aerosol applied at tillering stage of the crop had significant effects on grain yield. NH4Cl decreased (by 14.95%) and Sodium nitrite increased (by 21.74%) of grain yield. The varieties K-306>Ankur Omkar>Sonalika had variations in their grain yield. The treatments at the maximum tillering stage had significant effects on economic yield. NH4Cl and NaNO2 increased grain yield by 22.9% and 42.81% respectively at this stage. Varieties Ankur>K-306>Sonalika differed from each other in grain yield production. The application of N-aerosols at the reproductive development stage couldn’t change grain yield significantly.
In field experiment, the treatments had significant effects on economic yield of wheat crop (Figure 5). In general, NH4Cl could not change but NaNO2 decreased economic yield by 15.03% and 25.81% at 200 ppm and 400 ppm respectively. Lower was the concentration of the oxidised aerosol, higher was the production of yield of the crop. There were reductions in yield with application of aerosols at later stage (Stage1>Stage4>Stage3>Stage2).
Distribution of cations
Cations (Ca2+ and K+) present in intercellular and exchangeable sites varied significantly among the wheat varieties due to the aerosol treatments (Table 6). NH4Cl depleted more cations from the water free spaces and exchangeable sites than the oxidized nitrogen.
Peroxidase activity
The PO activity (Figure 6) in leaf of wheat (variety: Ankur Omkar) was determined in the field trial only. There were significant effects of the nitrogenous aerosols on PO at different DAS. The leaves treated with aerosol of oxidised nitrogen had higher PO (by 16.56% and 13.57%) than the reduced nitrogen (2.259% and - 1.83%) at 200 and 400 ppm respectively. The PO also increased commensuration with crop growth stages (Stage1 (37.03%)< Stage2( 4.82%)< Stage 3 (65.74%)<S4).q
 
Discussion
The present investigation into the impacts of oxidized and reduced nitrogen aerosols (viz., NaNO2 and NH4Cl respectively), applied at different growth stages of Wheat (Tritcum aestimum L.) crop, deals with physiological parameters contributing to higher grain yield production. We also attempted to sort out the most suitable variety and its stage responding positively to the aerosol of nitrogen. The mechanism(s) of injury to the varieties by the nitrogenous compounds are discussed in this paper [16].
In pot culture experiment, the simulated aerosols were NH4Cl @100 ppm (≅10 kgNha-1 yr-1) and NaNO2 @ 200 ppm (≅20 kgNha-1 yr-1) respectively. These were applied at different growth stages of wheat crop. We preferred the N-aerosols as foliar feeding to fumigating plants. The rate of Pn in wheat varieties varied significantly following foliar feeding. The Pn rate in crop varieties also different due to the differences in nitrogen input from the aerosols at their growth stages. There are several previous reports on Pn depression in higher plants by nitrogenous pollutants. A concentration at 0.6 μll-1 may cause Pn inhibition of oat (Avena sativa L.) and alfalfa (Medicago sativa L.) during 90 min fumigation [17]. Similarly there is evidence that decrease in Pn of bean (Phaseolus vulgaris) is related to 1-7 μll-1 NO2 over a period of 5 h [18]. Chloroplastic pH increases when the number of protons in the chloroplast exceeds the proton required (six) for a NO2 reduction. The key enzyme of carbon assimilation (ribulose-1-5- bisphosphate carboxylase/oxygenase) is pH dependent. Such changes in pH are likely to be harmful [19]. Photosynthetic depression has also been related to ultra structural changes in plants by NO2. The changes include protrusion from the chloroplast [20] and swelling of thylakoids [21]. Sodium and chloride ions might enter into cells, but they were neglected as non-physiological at relatively alkaline pH (>5.0) of the aerosols in our work.
The NR Nitrate activity in wheat was lowered in shoots by NH4Cl and NaNO2 at almost all stages of the crop. The varieties differed in respect of NR in their leaves. Nitrate reductase catalyses the reduction of nitrate to nitrite, and its levels of activity are determined by the supply of nitrate [22]. Inhibition of NR activity may be crop specific also [23]. The accumulation of larger amount of ammonium ions and certain amino acids in squash cotyledons during fumigation reduces NR activity [24].
In the present study, NUE in wheat increased with treatments of N-aerosols at their growth stages except a few. On an average, varieties also showed remarkable differences in their NUE in grains. However, NUE in grains decreased with the higher concentration of nitrogen aerosols in both pot culture and in field experiments. The differences between accessions in the response to N for physiological and phonological variables exists in case of Arabidopsis lyrata petrae [25]. Moreover we found that nitrogen nutrition enhanced grain yield of wheat varieties irrespective of their growth stages. The enhancement is more prominent in NaNO2 than NH4Cl fed plants. Higher nitrogen use efficiency with lower quantity of nitrogen from the source might improve nutritive quality of the crop varieties [26] but it showed a negative impact on productivity of cereal crops. The wheat varieties having higher grain yield were found with treatments at maximum tiller formation stage (60-90 DAS). In wheat, Ankur Omkar followed by K-306 and Sonalika emerged as commendable varieties. In these potential varieties, cell membrane stability was found to be higher irrespective of treatments. Cell membrane permeability was increased (with lower CMS) by both NH4Cl and NaNO2 as compared to control. As NH4Cl treated plants had higher leakage of ions from the cells, they possessed higher quantum of the cations in the intercellular and exchangeable sites. Similarly, NaNO2 treated plants had higher CMS and lower membrane leakage than NH4Cl treated plants, a lower amount of the cations were recovered from the cellular locations. The rate of PO activity of wheat crop treated with NaNO2 was higher than the rate shown by the NH4Cl treatment as compared to the control. Therefore, the membrane damages caused by NH4Cl and NaNO2 were brought by two different mechanisms. The former depleted the cations from the membrane directly and the later caused peroxidation of lipids present in the membrane. Hence, the membrane became leaky for the cations, and their quantum was higher in the intercellular and exchangeable sites irrespective of varieties, which were detected in the extraction processes with water and SrCl2 solutions respectively. Although, nitrite causes swelling of thylakoids and changes membrane stability, direct interference of free radicals with critical enzymes [27] may be responsible for reduction in growth and yield of crops. The oxides of nitrogen following the lipid breakdown in membrane cause cellular plasmolysis [28]. Apart from uncoupling electron transport chain in chloroplast [29], ammonia reduces cations viz., Calcium, magnesium, and potassium [30]. In plant cells, calcium is one of the integral components of plasma membrane, where it helps maintain stability [31]. Calcium ions binds with modulator proteins e.g. calmodulin [32], and serves as chemical signaling that in some cases equips the plant to resist external stresses [33]. These possibilities have not been explored meticulously in the present studies.
In the study, data were reproduced from pot and fields experiments in natural environmental conditions. The plants faced with varying in light intensity, temperature, relative humidity during their growth periods, and particularly during incubation period for measurement of net photosynthesis. It was clear from presentation of environmental data that none but the light intensity varied mostly (Figure 7). Light might have some roles on physiological variations and productivity of the crop stage-wise. There are differences between species imparting carbon dioxide fixation, and reduction of nitrite only at low light levels and high nitrite concentration [34]. So, the effects of irradiance, temperature and even desiccation on the pollution responses of the selected crop varieties and role of oxidative damage in these responses are important thrusts. All these largely indicate that the changes of the physiological parameters and productivity of the winter wheat crop may have quite different facets in context with the impacts of nitrogenous pollutants.
Acknowledgements
The authors express deep sense of gratitude to the Ministry of Environment and Forests, Govt. of India for providing necessary financial assistance to accomplish the various research works. We also acknowledge Assam Agricultural University for furnishing all required infrastructure and laboratory facilities in implementation of the research project in the Department of Crop Physiology, Jorhat, Assam.
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Susceptibility of Some Wheat (Triticum aestivum L.) Varieties to Aerosols of Oxidised and Reduced Nitrogen
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