Zinc (Zn (II) HEDTA) was used to determine their effect on salt-induced damages in maize plants. The aim of this study was to investigate the antioxidant capacity and the levels of enhanced total phenolic (TPC), total flavonoid (TFC) contents and their antioxidant activity in leaves of two maize cultivars Single cross 10 (SC10) and Single cross 162 (SC162) grown in two levels of salinity 0.00 and 100 mmol in response to 20 μmol Zn (II) HEDTA foliar spray treatments. Significant differences (P ≤ 0.05) in amounts of TPC ranged from (2.55 to 4.62 mg/gdw as Gallic) in Single cross 10 (SC10) and from (2.53 to 4.38 mg/gdw as Gallic) in Single cross 162 (SC162), TFC (ranged 1.53 to 2.41 mg/gdw as qurestien) in Single cross 10 (SC10) and from (1.28 to 2.41 mg/gdw as qurestien) in Single cross 162 (SC162) among all treated plants were observed. The levels of their compounds increase related to foliar spraying of Zn (II) HEDTA. A significant positive correlation between TPC, TFC and DPPH scavenging activity and iron chelating activity was observed which shows that phenolic compounds were involved in the mechanism of salt tolerance of the two cultivars by showing enhanced antioxidant activity which resulted in reduced membrane damage and hence improved growth. According to the results obtained, the adverse effects of salt stress on maize plants can partly be alleviated with application of Zn (II)-HEDTA chelates. It is concluded that the application of Zn (II) HEDTA to maize plants grown in salt conditions leads to the increase of antioxidant compounds and maize tolerance.
Salinity is one of the most important abiotic stresses affecting yield and quality of agricultural plants worldwide. Salinity may affect root uptake, translocation to shoots and physiological utilization of nutrients in plant. For example, [
To reduce AOS-induced damage, plants have evolved an antioxidative system, involving antioxidative enzymes, as well as low-molecular mass secondary metabolites such as phenolic compounds [
Zinc (Zn) is an important micronutrient essential for plant growth and development. One approach is the use of foliar spraying for increasing plant tolerance to salinity by alleviating Na+ and Cl− injury to plants [
The experiment was carried out at Fertilization Technology Department, National Research Centre, Cairo, Egypt, at Climatic Chamber (SNIJDERS SCIENTIFIC) donated by A.V. Humboldt Foundation, FR Germany. Seeds of two cultivars of maize Single cross 10 (SC10) and Single cross 162 (SC162) were washed and soaked for several hours in aerated tap water. The germination was carried out in plastic dishes at 28˚C in dark. Three days-old seedlings were put to grow in plastic pots filled with one-tenth concentration of Hoagland-Arnon solution (pH 6.0) containing 5 m MCa(NO3)2∙4H2O, 5 mM KNO3, 1 mM KH2PO4, 2 mM MgSO4∙7H2O and micronutrients in μM: H3BO3―10, MnCl2―0.5, ZnSO4―0.5, CuSO4―0.2, Na2MoO4―0.1, Fe (III)-HEDTA―20. The seedlings were grown in an environmental chamber under 12-h light at PPFD of 120 μmol∙m−2∙sec−1 provided by fluorescent tubes, 12-h night, 60% RH, at 25˚C day/20˚C night temperature. Two days later the plants were divided into four variants (plus and minus NaCl) with and without spraying Chelated Zn (20 umol) were applied for each pot. It was used to correct the nutrient imbalance caused by salt stress conditions. At 21 days old leaves were collected for different analysis.
2,2-Diphenyl-1-picrylhydrazyl (DPPH.) was purchased from Sigma Aldrich from Sigma-Aldrich (St. Louis,
MO). 3-(2-Pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4"-disulfonic acid monosodium salt (ferrozine) were purchased from Fluka (Buchs, Switzerland). All other chemicals and solvents were of the highest commercial grade and obtained from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China).
The total phenolic content (TPC) in maize extracts were determined spectrophotometrically according to [
Total flavonoids content (TFC) of maize extracts were spectrophotometrically determined by the aluminum chloride method using quercetin as a standard compound for preparation of calibration curve based on the formation of complex of flavonoid aluminum [
The method described by [
The capacity to scavenge the DPPH. radical was calculated using the following equation:
DPPH. scavenging effect (Inhibition %) =
where Ac was the absorbance of the control reaction and as the absorbance in the presence of the plant methanolic extract.
Metal chelating effects on ferrous ions was carried out as described by [
The percentage of ferrous ion chelating ability was calculated using the following equation:
Iron chelating activity (Inhibition %) =
where Ac was the absorbance of the control reaction and As the absorbance in the presence of the plant methanolic extract
Data were statistically analyzed according to [
Data presented in
Application of Zn (II) HEDTA in maize plants grown in salinized nutrient solution led to accumulation of high amounts of antioxidant compounds as compared to that in plants grown without NaCl. The highest levels of TPC (6.05 and 4.30) mg G/gdw and TFC (2.80, 2.41) mgQ/gdw were observed in Single cross 10 (SC10) and Single cross162 (SC162) respectively. Leaf phenolic contents are important protective components of plant cells. Accumulation may have been due to the reason that the accumulation of phenolics depends on plant growth stage and may act in vivo through different mechanisms in plant stress tolerance [
It is well known that, the higher concentrations of phenolics in Single cross 10 (SC10) can be explained by the accumulation of phenolic and flavonoids in stressed seedling of salt-tolerance Single cross 10 (SC10) than salt- sensitive Single cross 162 (SC162) cultivar. Thus, flavonoids may have a protective role under stress conditions. Exogenous application of Zn counteracted the harmful effects of salinity on non-enzymatic scavenging systems.
Application of Zn-Chelated increased the total phenols content in the leaves of two maize cultivars (
Single cross 10 (SC10) | ||
---|---|---|
Treatment | TPC mg/g | TFC mg/g |
Control | 2.83a ± 0.04 | 1.52a ± 0.09 |
NaCl | 4.62c ± 0.03 | 2.17b ± 0.11 |
Control + Zn-Ch | 4.39b ± 0.05 | 2.11b ± 0.11 |
NaCl + Zn-Ch | 6.05d ± 0.04 | 2.80c ± 0.12 |
LSD (0.05) | 0.15 | 0.36 |
All values with the same letter are not significantly different at p > 0.05; All values are the mean of three replicates ± SD.
Single cross 162 (SC162) | ||
---|---|---|
Treatment | TPC mg/g | TFC mg/g |
Control | 2.55a ± 0.05 | 1.28a ± 0.07 |
NaCl | 7.03d ± 0.06 | 3.06d ± 0.15 |
Control + Zn-Ch | 3.91b ± 0.08 | 1.85b ± 0.14 |
NaCl + Zn-Ch | 4.38c ± 0.06 | 2.41c ± 0.16 |
LSD (0.05) | 0.19 | 0.39 |
All values with the same letter are not significantly different at p > 0.05; All values are the mean of three replicates ± SD.
Generally, this study showed that the levels of phenolic and flavonoids content in maize cultivars were comparable to previous findings in several varieties of wheat located in Asia and North America [
However, it is know that varieties, agronomic, the part of the sampled and environmental factors had significant effect on the concentrations of antioxidant compounds in maize plant [
Free radical scavenging ability of methanolic extracts of the two cultivars of maize salinized plants in response to Zn (II) HEDTA foliar spray was measured with the change of absorbance caused by the reduction of DPPH radical, and results of the values of IC50 are shown in (
The methanolic extracts of two maize cultivars grown with NaCl combined with foliar spray of Zn (II) HEDTA exhibited appreciable Iron-chelating activity. The highest Fe-chelating activity were observed for extracts of Single cross 10 (SC10) stressed plants treated with Zn (II) HEDTA foliar spray ranged from (43.73 to 54.64 µg/ml) (
Inhibition % | |||||
---|---|---|---|---|---|
Treatments | 20 µg/ml | 50 µg/ml | 100 µg/ml | 150 µg/ml | 200 µg/ml |
Control | 4.72a ± 0.48 | 11.45a ± 0.18 | 23.38a ± 0.38 | 31.67a ± 0.36 | 42.73a ± 0.54 |
NaCl | 7.37c ± 0.36 | 15.70c ± 0.24 | 26.71c ± 0.30 | 38.25c ± 0.30 | 51.64c ± 0.25 |
Control + Zn-Ch | 6.30b ± 0.36 | 13.32b ± 0.36 | 24.34b ± 0.30 | 34.48b ± 0.24 | 47.52b ± 0.30 |
NaCl + Zn-Ch | 9.24d ± 0.30 | 18.51d ± 0.42 | 29.42d ± 0.28 | 40.39d ± 0.48 | 54.46d ± 0.24 |
EDTA standard | 42.41e ± 0.30 | 63.50e ± 0.43 | 75.51e ± 0.36 | 82.80e ± 0.42 | 91.56e ± 0.24 |
LSD (0.05) | 0.70 | 0.43 | 0.56 | 0.61 | 0.65 |
All values with the same letter are not significantly different at p > 0.05; All values are the mean of three replicates ± SD.
Inhibition % | |||||
---|---|---|---|---|---|
Treatments | 20 µg/ml | 50 µg/ml | 100 µg/ml | 150 µg/ml | 200 µg/ml |
Control | 3.37a ± 0.30 | 9.16a ± 0.36 | 19.74a ± 0.24 | 28.50a ± 0.48 | 40.39a ± 0.48 |
NaCl | 8.56c ± 0.24 | 17.48c ± 0.31 | 26.75c ± 0.36 | 39.79c ± 0.18 | 53.31c ± 0.48 |
Control + Zn-Ch | 5.35b ± 0.31 | 11.49b ± 0.42 | 24.65b ± 0.30 | 33.57b ± 0.36 | 47.52b ± 0.30 |
NaCl + Zn-Ch | 9.27d ± 0.54 | 20.49d ± 0.42 | 32.82d ± 0.36 | 46.37d ± 0.24 | 58.66d ± 0.36 |
EDTA standard | 42.41e ± 0.30 | 63.50e ± 0.43 | 75.51e ± 0.36 | 82.80e ± 0.42 | 91.56e ± 0.24 |
LSD (0.05) | 0.68 | 0.77 | 0.54 | 0.60 | 0.71 |
All values with the same letter are not significantly different at p > 0.05; All values are the mean of three replicates ± SD.
finding was in accordance with [
TPC and TFC exhibited a positive correlation with antioxidant scavenging properties (IC50) and Fe2+-chelating. Correlation coefficient of TPC, and TFC as well as DPPH. scavenging assay and Fe chelating for both cultivars (
Based on the results obtained, it might be concluded that foliar application of Zn (II) HEDTA improved the physiological and biochemical performance of maize plants in terms of increasing antioxidant compounds.
This work was done in the frame of the cooperation between National Research Centre (NRC) and Popov Institute for Plant Physiology Sofia-Belgaria (Egyptian Academy of Science and Technology-Bulgarian Academy of Science). It was supported by the Egypto-German Project “Micronutrient and other Plant Nutrition Problems “implemented by the National Research Centre (NRC) The project was supported by the Egyptian Academy of Science and Technology and the German Federal Ministry of Technical Cooperation (BMZ) through the German Agency For Technical Cooperation (GTZ).