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. 2011 May 26;17(3):215–222. doi: 10.1007/s12298-011-0067-5

The effects of selenium and other micronutrients on the antioxidant activities and yield of corn (Zea mays L.) under drought stress

Nour Ali Sajedi 1, Mohammad Reza Ardakani 2, Hamid Madani 3, Ahmad Naderi 4, Mohammad Miransari 5,✉
PMCID: PMC3550583  PMID: 23573012

Abstract

The effects of selenium (Se) on plant growth under drought stress and in the presence of micronutrients are yet to be investigated. Hence, in a field experiment in 2007 the effects of Se and micronutrients including iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), boron (B) and molybdenum (Mo) were evaluated on corn (Zea mays L.) grain yield under drought stress. Main- and sub-plots were devoted to irrigation (control and water stressed at the eight-leaf, blister and grain filling stages) and micronutrients treatments, respectively. Micronutrients were foliarly applied at 2 l ha-1 at the six-leaf stage, one week before tasseling, using a corn fertilizer, called biomin containing (on the basis of dry weight percentage) Fe (2.6), Zn (4.1), Cu (1.5), Mn (2.6), B (1.5), Mo (0.5) and Mg (4.1). Se was used as sodium selenite (Na2SeO3), at the rate of 20 g ha-1 two weeks before treating the plants with drought stress. Effects of drought stress on plant growth were determined based on the activity or level of antioxidants. With increasing the stress level, addition of Se or micronutrients significantly enhanced the antioxidant activity and level as well as corn grain yield. The interaction effects between Se and micronutrients adversely affected antioxidant activity as well as corn grain yield. Se addition at the grain filling stage resulted in the highest grain yield under drought stress. The single but not the combined use of Se or micronutrients can alleviate the unfavorable effects of drought stress on corn yield by affecting plant metabolism including antioxidant activity.

Keywords: Antioxidants, Corn (Zea mays L.) yield, Drought stress, Micronutrients, Selenium (Se)

Introduction

Environmental stresses, including drought, affect plant growth and yield production in different parts of the world (Chaves et al. 2002). Drought stress may increase the formation of free oxygen radicals, hydrogen peroxide and hydroxyl radicals resulting in the degradation of membrane components, the oxidation of protein sulfhydryl (-SH) group and the loss of membrane functions (Yao et al. 2009). Drought stress can adversely affect root and shoot growth resulting in the reduction of leaf surface area (Sajedi et al. 2010).

The production of various forms of active oxygen, due to stress, can also damage cellular constituents such as lipids, carbohydrates, proteins and nucleic acids. The oxidative stress of drought may also adversely affect the resistance of chlorophyll and caratenoid membrane and hence prevents the plant from photosynthetic and respiratory processes and the subsequent growth. By controlling the production and adverse effects of active oxygen in plant, enzymatic and non-enzymatic mechanisms can enhance plant resistance to drought (Bowler et al. 1992; Yao et al. 2009).

The activity of enzymes such as SOD, especially under stress, can affect the structure of activated species such as superoxide and hydrogen peroxide. This may eventually result in the degradation of cellular components. High amounts of such species are produced under stress. CAT, SOD and ascrobate peroxidase are enzymes, which are vital for the activities of organism. Under different conditions, including stress, these enzymes can continuously collect free radicals, which are the products of aerobic metabolites. Peroxidases are a collection of enzymes that catalyse the breakdown of H2O2 (Mittler 1993), preventing cellular peroxidation and other possible damages. Reduction of glutathione by GPX decreases H2O2 activity (Dixon 1998), especially under stress. Therefore, the collection of antioxidants can help the plant handle the stress.

Se is among the beneficial micronutrients, which is essential for the growth and activities of different organisms, except plants. Previous research has indicated the effects of Se on plant growth under different conditions including drought (Germ et al. 2007). Elemental Se is poisonous to the plant, however after absorption by root system and through metabolic processes it is converted to selenomethionine, and selenocysteine amino acids, which are not poisonous to the plant (Pilon-Smits et al. 2009). Dhillon (2002) found that Se affected the defense mechanism of living organisms.

Irrigation water enriched with Se significantly affected rice and sunflower growth. Se foliar application enhanced the production of plant antioxidants and the resistance to drought stress. Se alleviated the adverse effects of drought on plant growth and leaf water content in spring wheat (Triticum aestivum L.) (Kuznetsov et al. 2004). Addition of 18 g ha−1 Se solution as sodium selenite at the flowering stage increased the activities of SOD, GPX and CAT antioxidant enzymes (Rahimizadeh et al. 2007; Dadnia et al. 2008).

Some nutrients, including Fe, Zn, Cu, Mn, B and Mo are required for plant growth at micro amounts. Ionic forms of Fe, Zn, Cu, Mn, and Mg act as co-factors in many antioxidant enzymes. Under micronutrient deficiency the activity of antioxidant enzymes decreases, which in turn increases plant sensitivity to environmental stresses (Cakmak 2000). Similar to the other crop plants, corn (Zea mays L.) growth and production is influenced by environmental stresses such as drought. In addition, a variety of nutrients are necessary for corn optimum growth at different stages. Corn is among the crop plants, which are very sensitive to micronutrient deficiency. Movahed Dehnavi et al. (2002) indicated that application of micronutrient fertilizers can enhance plants resistance to environmental stresses such as drought and salinity.

Application of micronutrient fertilizers under severe drought stress increased the activities of SOD, GPX and CAT by 22 %, 79 % and 58 %, respectively (Rahimizadeh et al. 2007). Nutrient deficiency can adversely affect plant growth through inducing oxidative stress on plant growth (Yu and Rengel 1999). More specifically, researchers have very recently indicated the importance of metal ions in the activity of cell mitochondria. For example, their deficiency can influence mitochondria activity through inducing oxidative stress on the metal binding proteins (Tan et al. 2010). The beneficial effects of Se on plant growth under drought have been previously indicated, however its effects, in the presence of micronutrients, on corn growth under drought are yet to be investigated. Hence, this research work was conducted to address such effects on corn growth, with respect to the activity of antioxidants.

Materials and methods

Experimental procedure

A field experiment was performed in the Research Station of Islamic Azad University, Arak Branch, Iran, in 2007. Soil physical and chemical properties were determined for the depths of 0–30 and 30–60 cm, using the standard laboratory methods (Table 1). The acidity (pH) and electrical conductivity (EC) of a saturated paste was determined (Rhoades 1982). Using wet oxidation (Nelson and Sommers 1982) and Kjeldahl method (Nelson and Sommers 1973) soil organic carbon and nitrogen (N) were measured, respectively. Phosphorous (P) using bicarbonate extraction method (Olsen 1954) and potassium (K) using flamephotometer (emission spectrophotometery, Knudsen et al. 1982) were determined. Using atomic adsorption spectrometry (Model Perklin Elmer 3110) soil micronutrients including iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu) were measured according to the diethylenetriaminepentaacetic acid (DTPA) method (Baker and Amachar 1982). Soil texture was also determined using the hydrometery method (Gee and Bauder 1986).

Table 1.

Soil physical and chemical properties

Depth (cm) EC ds m−1 pH OC% N % P (ppm) K (ppm) Zn (ppm) Fe (ppm) Mn (ppm) Cu (ppm) Sand % Silt % Clay %
0–30 1.20 7.5 0.82 0.080 5 150 0.8 4.6 10.6 1.14 29 35 36
30–60 1.70 7.4 0.61 0.061 3.6 120 0.4 4 6.6 0.88 27 29 44
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EC: electrical conductivity, OC: organic carbon

The experiment was a split plot factorial on the basis of a completely randomized block design with four replicates. The main plots were four irrigation levels including control (full watering), drought stress at the vegetative (V8), blister or seed formation and at the pre mature seed stage or dough stage with the subplots being the combination of Se and micronutrients treatments. Plants were subjected to the drought stress treatment at each growing stages by not watering the plots for a certain period of time and re-irrigating when 180 mm water had been evaporated from the basin pan. Full irrigation was arranged based on the amount of crop water requirement and the measured daily evaporation from the basin pan. Plots were irrigated using polyethylene tubes in which the amounts of water were controlled using water contour.

Corn plants were foliarly fertilized with micronutrients one week before tasseling at the six-leaf stage at two liter ha−1 using a corn fertilizer, called “biomin” (JH Biotech Inc.) containing (on the basis of dry weight percent) Fe (2.6), Zn (4.1), Cu (1.5), Mn (2.6), B (1.5), Mo (0.5) and Mg (4.1). Se was used as sodium selenite (Na2SeO3), at the rate of 20 g ha−1 two weeks before subjecting the plants to the drought stress treatment (Dadnia et al. 2008).

Corn seeds were planted 20 cm apart in 6-m rows, with a 75-cm spacing. To prevent any likely side effects, the two side lines between the plots were not planted. The amounts of fertilizers were determined according to soil testing analysis and one third of N and all of P was applied at seeding and the remaining N was fertilized twice during the vegetative stage. Ten sample plants were harvested from the middle of each plot at physiological maturity when a black layer was formed on the seed base.

Enzymatic bioassay

Sampling

For the measurement of enzyme activity and content, three leaf sample were collected from the sampled plants, and were then washed, frozen and stored using liquid N2 at −80 °C for further analyses.

Extract preparation

Using a mortar and pestle, leaf samples were homogenized with ice-cold extraction buffer (25 mM sodium phosphate, pH 7.8). The homogenate was then centrifuged at 18,000 g for 30 min at 4 °C (the temperature for all operations) and the supernatant, which was used as a crude extract for the enzyme bioassay, was filtered using a filter paper.

Antioxidant bioassay

Catalase activity was measured by the method of Cakmak and Horst (1991). The reaction mixture contained 100 μl crude enzyme extract, 500 μL 10 mM H2O2, and 1,400 μL 25 mM sodium phosphate buffer. The decrease in the absorbance at 240 nm was recorded for 1 min by spectrophotometer (model Cintra 6, GBC Scientific Equipment, Dandenong, Victoria, Australia). CAT activity of the extract was expressed as CAT units per milligram of protein. Superoxide dismutase activity was determined with the reaction mixture containing 100 μL 1 μM riboflavin, 100 μL 12 mM L-methionine, 100 μL 0.1 mM EDTA (pH 7.8), 100 μL 50 mM Na2CO3 (pH 10.2) and 100 μL 75 μM nitroblue tetrazolium (NBT) in 2,300 μL 25 mM sodium phosphate buffer (pH 6.8), and 200 μL crude enzyme extract with the final volume of 3 mL.

SOD activity was assayed by measuring the ability of the enzyme extract to inhibit the photochemical reduction of NBT glass test tubes with the mixture as were illuminated with a fluorescent lamp (120 W); identical tubes, which were not illuminated were used as blanks. After illumination for 15 min, the absorbance was measured at 560 nm. One unit of SOD was defined as the amount of enzyme activity that was able to inhibit the photo reduction of NBT to blue formazan by 50 %. The SOD activity of the extract was expressed as SOD units per milligram of protein. Peroxidase activity was determined by the oxidation of guaiacol in the presence of H2O2. The increase in absorbance was recorded at 470 nm (Hernandez et al. 2000). The reaction mixture contained 100 μL crude enzyme, 500 μL H2O2 5 mM, 500 μL guaiacol 28 mM, and 1,900 μL potassium phosphate buffer 60 mM (pH = 6.1).

Lipid peroxidation was determined by estimating the malondialdehyde (MDA) content in 1 g leaf fresh weight according to Madhava Rao and Sresty (2000). MDA is a product of lipid peroxidation by thiobarbituric acid reaction. The concentration of MDA was calculated from the absorbance at 532 nm (correction was done by subtracting the absorbance at 600 nm for unspecific turbidity).

Statistical analysis

Data were subjected to the analysis of variance using SAS (SAS Inc. 1988) and means were compared using Duncan’s multiple range test (Steel and Torrie 1980).

Results

According to the analysis of variance the effects of drought stress on the activity of antioxidants and corn grain yield were significant at different growth stages at P = 0.01. However, Se addition just significantly affected the activity of antioxidants and not crop yield. The results also indicated that the activity of SOD, MDA content and corn grain yield was significantly affected by the interaction effects of drought and Se. Micronutrients significantly affected the activity of antioxidants and corn grain yield. The two way interaction effects of drought and Se significantly affected MDA content and in the case of Se and micronutrients, CAT and GPX were significantly affected. Their three way interaction significantly affected just corn grain yield (Table 2).

Table 2.

Analysis of variance for the effects of experimental treatments on the activities of antioxidants and corn grain yield

S. O. V df SOD CAT GPX MDA Grain yield
Replication 3 21,928.52 ns 18.417 ns 0.46 ns 0.01 ns 20,634.1ns
Water level (L) 3 567,191.97** 1,377.07** 212.38** 3.24** 18,890,861.9**
Error 9 15,982.00 27.58 1.69 0.08 512,256.9
Selenium (Se) 1 1,814,072.27** 2,618.88** 226.50** 5.71** 355,040.3 ns
L × Se 3 113,933.22* 91.10 ns 6.59 ns 0.21** 11,963,794.9**
Micronutrients (M) 1 1,115,400.07** 1,681.00** 236.39** 2.91** 1,647,468.5*
L × M 3 27,342.56 ns 23.07 ns 7.44 ns 0.29** 966,299.7 ns
Se × M 1 86,215.64 ns 216.83* 46.92* 0.06 ns 1,374,961.4 ns
L × Se × M 3 27,467.43 ns 14.01ns 10.57 ns 0.12 ns 2,684,642.4**
Error 36 33,378.78 49.93 9.20 0.04 365,658.4
C V % – 14.31 7.82 18.98 16.22 8.92
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ns, * and ** : not significant, significant at 5 and 1 % level of probability, respectively. S.O.V.: source of variation.

SOD Superoxide dismutase; CAT Catalase; GPX Glutathione peroxidase; MDA Malondialdehyde

Mean comparison of main effects indicated that drought stress at different levels significantly enhanced the activity of antioxidants, compared with the control treatment and it resulted in significant reduction in corn grain yield. Averaged across the other two experimental parameters, addition of Se and other micronutrients decreased the activities of antioxidants (Table 3).

Table 3.

Mean comparison of antioxidants and corn grain yield, as affected by the main effects of experimental treatments

Treatment SOD (μmol/mg protein) CAT (μmol/mg protein) GPX (μmol/mg protein) MDA (nmol/g fresh weight) Grain yield (kgha−1)
L1 1,024.19c 79.04d 12.71d 0.78d 8,025a
L2 1,240.69b 87.94c 14.09c 1.07c 6,989b
L3 1,417.00a 93.21b 16.07b 1.54b 6,712b
L4 1,423.69a 101.13a 21.04a 1.78a 5,386c
Se0 1,444.75a 96.73a 17.86a 1.59a 6,852a
Se1 1,108.03b 83.93b 14.10b 0.99b 6,703a
M0 1,408.41a 95.46a 17.60a 1.51a 6,618b
M1 1,144.37b 85.21b 14.06b 1.08b 6,938a
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SOD Superoxide dismutase; CAT Catalase; GPX Glutathione peroxidase; MDA Malondialdehyde.

Mean values, followed by the same letters within each column are not significantly different using Duncan’s multiple rang test at P = 0.05, L1: control L2: drought stress at V8 Stage, L3: drought stress at blister stage, L4: drought stress at grain filling stage, Se0: Without Selenium, Se1: with Selenium M0: without micronutrients M1: with micronutrients

SOD activity ranged from 1,024 to 1,424 μmole/mg.protein at control to the highest level of drought. For CAT and GPX the corresponding ranges were equal to 79 to 101 and 12.7 to 21 μmol/mg protein, respectively. MDA content on the basis of nmol/g fresh weight ranged from 0.78 to 1.78 and for the grain yield the corresponding values were in the range of 8,025 (control treatment) to 5,386 kg ha−1 (the highest drought level) (Table 3).

Se addition decreased the activity of SOD from 1,445 to 1,108, CAT from 97 to 84 and GPX from 18 to 14 μmol/mg protein. Se reduced MDA content from 1.6 to 1.0 nmol/g fresh weight and the grain yield from 6,852 to 6,703 kg ha−1. The reduction resulted by micronutrient addition was from 1,408 to 1,144 for SOD, 95.5 to 85.2 for CAT and 18 to 14 μmol/mg protein for GPX. Micronutrients reduced MDA content from 1.5 to 1.1 nmol/g fresh weight and increased corn grain yield from 6,618 to 6,938 kg ha−1. All the differences were statistically significant (Table 3).

Interestingly, while the addition of Se at control treatment decreased the activity of antioxidant enzymes, under stress Se significantly enhanced their activity. For example at the highest level of drought the activity of SOD, CAT and GPX increased from 1,129 to 1,718, 91 to 111, and 19 to 23 μmol/mg protein, respectively. The corresponding increases for MDA and corn grain yield were equal to 1.33 to 2.23 nmol/g fresh weight and 4,458 to 6,314 kg ha−1, respectively. The same trend was observed for micronutrient addition, although it decreased corn grain yield at different levels of drought. Micronutrient treatment at different levels of Se resulted in significant reduction of antioxidant activity or level as well as corn grain yield (Table 4).

Table 4.

Mean comparison of antioxidants and corn grain yield, as affected by the two way interaction effects of experimental treatments

Treatment SOD (μmol/mg protein) CAT (μmol/mg protein) GPX (μmol/mg protein) MDA (nmol/g fresh weight) Grain yield (kg ha−1)
Water level Selenium
L1 Se0 1,159.37d 85.09de 14.07cd 0.99d 9,144a
Se1 889.00e 72.99f 11.35d 0.58e 6,905bc
L2 Se0 1,113.75d 83e 12.80cd 0.85d 6,618c
Se1 1,367.62bc 92.89bc 15.39c 1.30c 7,361b
L3 Se0 1,300.12cd 88.49cde 13.56cd 1.22c 6,595c
Se1 1,533.87ab 97.94d 18.57b 1.86b 6,829bc
L4 Se0 1,129.25d 91.26bcd 18.67b 1.33c 4,458d
Se1 1,718.12a 111a 23.40a 2.23a 6,314c
Water level Micro-nutrients
L1 M0 1,148.25b 85.53cd 13.85cd 0.97d 7,841a
M1 900.12c 72.54e 11.57d 0.60e 8,208a
L2 M0 1,162.87b 83.86d 11.96d 1.03cd 7,153b
M1 1,318.50b 92.02bc 16.22bc 1.11cd 6,826bc
L3 M0 1,263.75b 87.45cd 13.32cd 1.19c 6,995bc
M1 1,570.25a 98.97ab 18.81b 1.90a 6,429c
L4 M0 1,250.75b 96.97b 19.36b 1.51a 5,765d
M1 1,596.62a 105.29a 22.71a 2.06a 5,007e
Selenium Micro-nutrients
Se0 M0 1,540.06a 100.01a 18.92a 1.78a 6,717b
M1 1,349.44b 93.44b 16.79a 1.41b 6,690b
Se1 M0 1,276.75b 90.90b 16.87a 1.24c 7,159a
M1 939.31c 76.97c 11.32b 0.75d 6,545b
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SOD Superoxide dismutase; CAT Catalase; GPX Glutathione peroxidase; MDA Malondialdehyde

Mean values, followed by the same letters within each column are not significantly using Duncan’s multiple rang test at P = 0.05, L1: control L2: drought stress at V8 Stage, L3: drought stress at blister stage, L4: drought stress at grain filling stage, Se0: Without Selenium, Se1: with Selenium, M0: without micronutrients, M1: with micronutrients

The three way interaction effects interestingly indicated that Se can effectively alleviate the stress of drought on corn yield, especially at the highest level of drought as the amount of yield increased to 6,818 kg ha−1, significantly different from the other treatments. At control, addition of Se or/and micronutrients decreased the activity or content of antioxidants, which was not the case for drought treatments. In addition, there were interactions effects between Se and micronutrients, as addition of micronutrients with Se significantly decreased the activity of antioxidants activities and corn grain yield at different drought levels, while their single application significantly increased the activity and level of antioxidants (Table 5).

Table 5.

Mean comparison of antioxidants and corn grain yield, as affected by the three way interaction effects of the experimental treatments

Treatment SOD (μmol/mg protein) CAT (μmol/mg protein) GPX (μmol/mg protein) MDA (nmol/g fresh weight) Grain yield (kgha−1)
L1Se0M0 1,262.25cde 89.95cdef 14.72cd 1.20d 8,769ab
L1Se0M1 1,056.50ef 80.22fg 13.42cde 0.77e 9,519a
L1Se1M0 1,034.25ef 81.12fg 12.97cde 0.73e 6,914cde
L1Se1M1 743.75g 64.85h 9.72e 0.43f 6,898cde
L2Se0M0 1,293.50cde 90.95cdef 13.67cde 1.2n 6,146def
L2Se0M1 1,441.75bc 94.82bcd 17.10bc 1.37cd 7,089cd
L2Se1M0 1,195.25cde 89.22cdef 15.35c 0.86e 8,159b
L2Se1M1 1,032.25ef 76.77g 10.25de 0.85e 6,562cdef
L3Se0M0 1,405.25bcd 92.85bcde 16.27bc 1.55bc 7,243c
L3Se0M1 1,662.5ab 103.02ab 20.87ab 2.18a 5,947ef
L3Se1M0 1,478.00bc 94.92bcd 16.75bc 1.62bc 6,747cdef
L3Se1M1 1,122.25def 82.05efg 10.37de 0.83e 6,912cde
L4Se0M0 1,642.50ab 109.75a 23.80a 2.11a 4,712g
L4Se0M1 1,793.75a 112.25a 23a 2.36a 4,202g
L4Se1M0 1,399.50bcd 98.32bc 22.42a 1.75b 6,818cde
L4Se1M1 859.00fg 84.20defg 14.92cd 0.90e 5,810f
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SOD Superoxide dismutase; CAT Catalase; GPX Glutathione peroxidase; MDA Malondialdehyde

Mean values, followed by the same letters within each column are not significantly using Duncan’s multiple rang test at P = 0.05, L1: control, L2: drought stress at V8 Stage, L3: drought stress at blister stage, L4: drought stress at grain filling stage, Se0: Without Selenium, Se1: with Selenium, M0: without micronutrients, M1: with micronutrients

Discussion

When plants are subjected to different stresses, the activity of antioxidants are increased to alleviate the stress through degrading the products of stress including free radicals such as superoxide and peroxide, which are not favorable to plant growth (Cakmak 2000; Habibi et al. 2004; Rahimizadeh et al. 2007). Therefore, determination of antioxidants activity in plants can be used as a useful indicator for plant response to the stress and accordingly the appropriate ways of alleviating stress can be suggested. In this experiment the effects of drought stress on the activity of antioxidants (as indicators of drought stress) and corn grain yield were evaluated and the single and combined effects of Se and micronutrients to alleviate the stress were tested. There is little data regarding such effects.

According to the results of this research work, Se had negative effects on the activity of antioxidants at the control level of drought; however it significantly increased the activity of antioxidants at the stressed treatments, which is also indicated by the significant interaction effect between Se and drought on the activity of antioxidants (Table 2). These results are in agreement with Shen et al. (2008). Such enhancing effects of Se on the activity of antioxidants have been attributed to the antioxidant activity of selenoproducts and the upregulating effects of Se on the genes responsible for the related stress mechanisms (Hartikainen 2005).

Se can also affect plant growth through influencing the production of jasmonic acid and the stress hormone ethylene and the proteins, which affect the plant resistance versus pathogens and sulfate/selenite production (Tamaoki et al. 2008). GPX contains Se in its structure, which can influence the enzyme activity. The increase in the activities of antioxidants under drought stress with Se addition is in agreement with the results of other researchers (Bailly et al. 2000; Habibi et al. 2004; Rahimizadeh et al. 2007). Metal ions such as Fe, Mn, Cu, Zn, and Mg are essential for plant growth and production; because they are necessary for many plant activities and are the cofactors for most antioxidant enzymes. Based on the type of their metal cofactor (Cu or Mg, Mn or Fe) SOD enzymes are categorized (Yu and Rengel 1999).

CAT has iron in its structure and catalyses the turn of hydrogen peroxide to oxygen and water. CAT reduces hydrogen peroxide by reduced gluthatione, resulting in the protection of cellular damage from oxidative processes (Marschner 1995; Cakmak 2000). Our results are also in agreement with Wang et al. (2004) and Rahimizadeh et al. (2007) who indicated that application of micronutrients can alleviate the adverse effects of stresses such as salinity and drought on plant growth. Micronutrient presence in the structure of antioxidants (Yu and Rengel 1999; Allen et al. 2007), their important effects on the cellular respiration (Tan et al. 2010), and their deficiency under drought make their application necessary under different conditions, including stress (Hu and Schmidhalter 2005).

At the control level of water stress, addition of Se or micronutrients decreased the antioxidants activities or corn grain yield. This may be due the toxic effects of Se or micronutrients on plant growth, especially at higher concentration. However, with increasing the level of stress the application of Se (Xue et al. 2001) or micronutrients significantly enhanced the antioxidants activities and corn grain yield indicating that there are interaction effects between the drought stress and Se (Shen et al. 2008) or micronutrients. Se or micronutrients under stress can help the plant to utilize the mechanisms, which eventually result in the production of antioxidants, more effectively. Researchers have indicated that under drought stress, in addition to enhancing the level of antioxidants, Se can also enhance plant resistance to the stress by increasing the amount of proline in plant (Khattab 2004).

The combined use of Se and micronutrients adversely affected the antioxidants activities and corn grain yield indicating that there are some kind of antagonistic effects between Se and micronutrients and their combined use is not recommendable under drought stress. It is likely that the presence of each may interrupt the functioning of the other (Singh and Singh 1978; Yang et al. 2007).

According to the mean comparisons Se addition resulted in the highest amounts of antioxidants during the grain filling stage. This can be attributed to the reduction in plant absorption and hence less water availability for metabolic activities during the final period of plant growth. Therefore, the antioxidant activities might have increased to alleviate probable damages caused by water stress (Rahimizadeh et al. 2007).

Conclusion

According to the results of this research work, addition of Se or micronutrients is recommendable for increased corn production under drought stress as such use can enhance the activities of antioxidants and hence protect the plant from oxidative damage. However, the combined use of Se and micronutrients are not suggested because the antagonistic effects between the two treatments decreased antioxidant activities and corn grain yield.

Abbreviations

SOD, EC 1.15.1.1

Superoxide dismutase

CAT, EC 1.11.1.6

Catalase

GPX, EC 1.11.1.9

Glutathione peroxidase

MDA

Malondialdehyde

N

Nitrogen

P

Phosphorous

Mg

Magnesium

Fe

Iron

Zn

Zinc

Mn

Manganese

Cu

Copper

B

Boron

Mo

Molybdenum

Se

Selenium

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