International Journal of Agriculture and Crop Sciences. Available online atwww.ijagcs.com IJACS/2012/4-10/622-626 ISSN 2227-670X ©2012 IJACS Journal
Effect of different ratios of nitrate and ammonium on photosynthesis, and fatty acid composition of canola under saline conditions Ahmad Bybordi Research Center of Agriculture and Natural Resources of East Azerbaijan, Tabriz, Iran Corresponding author email:
[email protected] ABSTRACT: In order to evaluate effects of different ratios of ammonium and nitrate, on photosynthesis, respiration and fatty acid composition of canola under conditions of salt stress a greenhouse experiment was conducted in Agriculture Research Center of Eastern Azerbaijan, Iran on 2009. The experimental design was completely randomized design arranged in factorial. The first and second factor included four differing ratios of nitrate to ammonium namely 0:100, 25:75, 50:50 and 75:25 and salinity stress namely 0 and 200 mM NaCl, respectively. The results demonstrated that the highest wet and dry weight, leaf area, relative water content, photosynthesis ratio, transpiration ratio and leaf potassium content were obtained from those plants which were treated with nitrate and ammonium in 50:50 ratio under non saline condition. Salinity significantly decreased wet and dry weight, leaf area, relative water content, photosynthesis and respiration ratio and leaf potassium content. It seems that 50:50 ratio protects plants from salinity stress. On the other hand fatty acids content increased on account of salinity stress. In addition, in high ammonium ratios fatty acid content were considerably more than high nitrate ratios. Furthermore, the highest fatty acid content was obtained from 25:75 ratios in other word high ammonium treatments. Keywords: Canola, Salinity, Nitrate to ammonium ratio, Fatty acid composition INTRODUCTION Oilseed plants are second food sourceafter cereals in the world. In spite of high fatty acid content, these plants contain high protein content. Canola (Brassica napus L.) is one of the most important oil seeds in the world. Statisticsshow that canola is in the third rank after soybean and oil palm in the world (6). Obtained oil from canola has desirable proportion of fatty acids. Canola oil with low level of saturated fatty acids (7%) and high level of unsaturated fatty acids (61%)is one of the best oils for human diet (Bybordi,2010; Gashaw and Mugwira ,1981). Salt stress is one of the most important and common abiotic stresses which limits agricultural products and decreases efficiency of arid and semi-arid lands (Ikeda and OsawaT,1983). There are extensive disorders in plant cells created by soil salinity. In other word soil salinityleads to sodium and chlorine accumulation in plant tissues and affect on mineral absorption via competitive interactions or membrane permeability(Bybordi and Tabatabaei,2012;Alan,1989). Salt resistance is included some complex traits and these traits are correlated with physiological characteristics of plant (Rothestein and Cregg ,2005).Fatty acids in seeds are often in the form of acylglycerol. Canola oil characteristics are depends on fatty acid composition. Romero (1991) found that fatty acid composition in Brassica rapa, a species with low level of erucic acid, changes considerably at seed filling stage or 15-36 days after pollination so that oleic acid content increases andpalmitic, stearic and linolenicacid content decreases during this period. Saturated fatty acids content is affected by temperature and nutrition during seed filling and oil accumulation.When nitrogen is applied in the form of nitrate fertilizers, plants are more able to absorption and consumption of it. Nonetheless, Malhai and co-workers (1998) showed that canola can use ammonium easily. Grant and Bailey (1993) have been reported that application of nitrate and ammonium in equal proportion increases unsaturated fatty acids in canola. Numerous studies have been done regarding effects of different proportion of nitrate and ammonium on growth, photosynthesis and nitrogen metabolism of plants under salinity stress (Grant and Bailey , 1993; Lewis et al 1989; Mannervik and Gutenberg ,1981; Mohsenabadi ,1999). Recent studiesshow that application of high proportion of ammonium increases aldehyde oxidase and xanthine dehydrogenase enzyme activity under conditions of slat stress(Malhai et al .1988; Mohsenabadi ,
Intl J Agri Crop Sci. Vol., 4 (10), 622-626, 2012 1999; Pill and Lambeth ,1977). In saline soils nitrate uptake and consumption occur slowly due to ionic interactions across the root cell membrane(Rhamani and MajidiHervan , 2002). In this study different proportions of nitrate and ammonium were applied on canola plants grown under salinity stress and some physiological responses and fatty acid compositions were studied. MATERIALS AND METHODS Current study was conducted in Agriculture Research Center of Eastern Azerbaijan, Tabriz, Iran on 2008. The experimental design was completely randomized design arranged in factorial with three replications. The first and second factor included four differing ratios of nitrate to ammonium namely 0:100, 25:75, 50:50 and 75:25 and salinity stress namely 0 and 200 mMNaCl, respectively. Canola seeds (c.v SLM046) were sown in 5 liter plastic pots filled with 1:1 perlite and vermiculite and placed in green house. Light intensity was adjusted on 13000 and 32000 Lux in spring and summer, respectively. Day/Night temperature was fixed on C during experiment. Canola plants were irrigated with Hoagland solution twice a week(Ikeda and OsawaT ,1983; Hoagland and Arnon ,1950). Salt stress was induced by 200 mMNaCl solution. Nitrogen was supplied from ammonium and nitrate sources. Different proportion of ammonium and nitrate are shown in table 1 (Tabatabaei et al.2006). Electrical conductivity of nutrition solutions was adjusted on 6.5-6.8 dS.m-1using sulfuric acid. The photosynthesis and transpiration ratios were measured by photosynthesis meter (Da-10101, Germany). Light unit was 1000 µmol.m-2.S-1 and CO2 entrance flow adjusted at 500 ml.min-1. All measurements were done between 9:00 to 14:00 (Tabatabaei et al.2008).Fully expanded and healthy leaves were selected and photosynthesis and transpiration was measured three times. Leaf area was measured using leaf area meter (Li3100c, Licor, United states of America). Wet and dry weight was registered by digital scale and thus potassium and sodium content was determined by flame photometry method. In addition, relative water content in then-day leaves was estimated according to equation 1. fw − Dw Equation 1: RWC = ( ) × 100 tw − Dw Gas chromatography is the best method to identify fatty acids (Francois and Kleiman ,1990). After oil extraction, 0.1 g oil was mixed with 3 ml heptane, after 20 min shaking upon phase was separated and injected to gas chromatograph. Chromatography was performed with Varian-CP-3800 gas chromatograph equipped with a 30 m × 0.25 mm i.d.capillary column (EC-1000) coated with a 0.25 m film of HP-23. Split injection (split ratio 1:50) was performed, with nitrogen as carrier gas at a flow rate of 2.1 m.s-1and at the pressure of0.76 bar. The injection port temperature was 250°C. All data for all parameters was carried out using SPSS software. Differences between mean values were determined with Duncan’s Multiple Range Test and P value was P < 0.05. RESULTS AND DISCUSSION Different proportion of ammonium to nitrate had significant effect on wet and dry weight (Table 2). The highest wet weight was obtained from those plants which were treated with 50:50 ratios under normal conditions (Table 3). Decrease of wet weight due to salt stress was slower when 50:50 ratios were applied (Table 3). It seems that on the one hand ammonium increases oxidase enzyme activity and on the other hand nitrate protects plants from detrimental effects of salinity via creating ionic interactions(Gashaw and Mugwira ,1981;Bybordi, 2010). It has been reported that under conditions of salt stress, application of ammonium and nitrate in equal proportion helps to alleviate detrimental effects of salt stress and improvingof assimilation and biomass production (Wang et al.1998). Relative water content was affected by different proportion of ammonium and nitrate (Table 2). The highest relative water content was obtained from those plants which were treated with 50:50 or 0:100 ratios (nitrate to ammonium)under normal conditions (Table 3). Salt stress decreased relative water content dramatically. Decrease of relative water content due to salt stress was slower when 50:50 ratios were applied (Table 3). Under conditions of salt stress cell elongation rate and turgidity decreases and thus cell wall get hard and thick (Bybordi et al.2010). Reducing of relative water content was negligible when 50:50 ratios were applied it can be due to activation of some cellular mechanisms to produce soluble sugars, proline and glycine which are effective in cell water adjustment (Guerzoni et al .2001). Moreover, the highest leaf area was measured in those plants which were treated with 50:50 ratios without salinity stress (Table 3). Decrease of leaf area due to salt stress was slower when 50:50 ratios were applied (Table 3).Some researchers have reported that cytokininsynthesis increased when nitrate and ammonium were applied at same amount. It seems that increase of leaf area is related to increase of cytokininsynthesis because of equal ratios of nitrate and ammonium (Hawkins et al.1993). Table 1. Nutrient solution used for growing canola (mM) 623
Intl J Agri Crop Sci. Vol., 4 (10), 622-626, 2012 NO3 : NH4
Salts
100:0 5.7 4.3 2 1 0 0 1 0
KNO3 Ca(NO3)2 MgSo4 KH2PO4 NH4H2PO4 NH4Cl KCl NaCl2
75:25 5.4 2.7 2 0 1 2.6 2.3 1.5
50:50 0 3.6 2 0 1 6.2 7.7 0.7
25:75 0 1.8 2 0 1 9.8 7.7 2.4
Table 2.Analysis of variance some canola traits and fatty acids affected by NO3: NH4 ratios and salt stress S.O.V
df
Wet weight
Dry weight
NO3: NH4 ratio Salinity Interaction Error
3
16.06**
10.21**
1120925.28**
22.60*
1 3 16
54** 3.22* 0.51
32* 4.26* 0.61
92411775.28** 6189756.78* 152256.84
48.61** 6.96* 1.36
S.O.V
df
Palmitoleic acid
Oleic acid
Linoleic acid
Linolenic acid
3
6.36**
4.26**
9.48**
1 3 16
9.46** 2.88* 0.60
6.81** 1.12* 0.46
11.66** 3.66* 0.82
NO3: NH4 ratio Salinity Interaction Error
Leaf area
RWC
Photosynthesis
Respiration
Potassium
Sodium
Palmitic acid
39.83**
28.78**
48.61**
10.50**
39.24**
481.80** 7.64* 1.50
40.72** 9.6* 0.64
22.41** 11.6* 2.36
18.6** 4.26* 0.72
48.66** 12.14* 1.36
Arachidic acid
Eicosenoic acid
Erucic acid
Stearic acid
gadoleic acid
3.86**
2.72**
1.86**
1.26**
1.17**
1.21**
6.91** 1.72* 0.56
5.46** 1.61* 0.36
4.31** 1.41* 0.32
3.21** 1.10* 0.26
2.16** 0.96* 0.22
2.11*8 0.92* 0.19
and ns: significant at 0.05, 0,01 probability level and no significant Table 3.Effect of NO3: NH4 ratios and salt stress on some canola traits NO3: NH4 100:0 75:25 50:50 25:75
Salinity 0 mM 200 mM 0 mM 200 mM 0 mM 200 mM 0 mM 200 mM
Wet weight (g per plant) 43.8b 29.5c 53.4ab 43.2b 58.7a 45.2b 44.2b 33.4c
Dry weight (g per plant) 9.5c 6.6d 13.5ab 9.2c 14.6a 12.5b 8.6c 5.2d
Leaf area (cm)
RWC (%)
Photosynthesis 2 -1 (µmol.m .s )
Transpiration 2 -1 (µmol.m .s )
Potassium -1 (mg.g )
Sodium -1 (mg.g )
665.5c 631c 1044ab 710bc 1133a 976b 655c 561d
93a 81b 91ab 79c 93a 82b 90ab 78c
15.5ab 6.8c 15.1ab 6.2c 16.8a 7.2c 14.8b 5.8c
6.8ab 2.1c 6.5b 2c 6.9a 2.3c 6.2b 1.8c
34ab 17c 32b 16c 36a 19c 30b 15c
7.5c 33a 8c 32a 7.8c 26b 7.7c 28b
Values in columns with the same letter are no significantly different. p
