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Exogenous Salicylic Acid and Thiourea Ameliorate Salt Stress in Wheat by Enhancing Photosynthetic Attributes and Antioxidant Defense

Sumaiya Farzana
Graduate Training Institute, Bangladesh Agricultural University, Mymensingh 2202; Department of Biochemistry and Molecular Biology, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Md. Rasel
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Salinity stress is a worldwide problem, constraining global crop production seriously. Recent global climate change has made this situation more serious. Exogenous application of potential protectants such as salicylic acid (SA) and thiourea (TU) can be an important approach to alleviate the adverse effects of salinity stress on plants. Therefore, a hydroponic experiment was conducted to investigate the ameliorating effect of SA and TU on salt stress in a wheat genotype namely BARI Gom-30 considering the growth traits, photosynthetic parameters and antioxidant enzyme activities. The experiment was laid out by following randomized complete block design (RCBD) with three replications and five treatments viz., control, salt, salt + SA, salt + TU, and salt + SA + TU. Salinity stress caused significant reduction of different growth traits such as plant height, shoot and root length, fresh weight and dry weight of root and shoot in wheat genotype. The leaf water status, different photosynthetic parameters and intracellular proline contents were severely shortened in the leaves of salt stressed plants. However, exogenous application of SA or TU on salt stressed wheat plants showed a significant increase in growth traits by up regulating the levels of chlorophyll content, photosynthetic pigments and proline contents in comparison to salt treated plants alone. The higher Na+/K+ was noted in the leaves of stressed seedlings and therefore, the wheat plants suffered more oxidative damage due to the higher production of H₂O₂ and MDA under salinity stress. Besides these, the activities of antioxidant enzymes namely CAT, POD and APX were slightly enhanced due to the imposition of salt on wheat seedlings compared to control treated plants. In contrast, SA or TU mediated ameliorating effect of salt stress maintained the lower Na+/K+ as well as the minimum production of H₂O₂ and MDA in BARI Gom-30. This is might be due to the higher increment of CAT, POD and APX enzyme activities in the stressed wheat genotypes supplemented with SA or TU reflecting the positive role of SA or TU against salt-induced oxidative stress in BARI Gom-30. Individual foliar application of SA and TU was found to be more effective in improving salt stress tolerance in BARI Gom-30 than that of the combined application of SA and TU.

Keywords: Wheat, Salinity, Hydroponic culture, Proline contents, Antioxidant enzymes

Location: Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Wheat, Soil salinity

Objectives:

To examine the positive role of SA and TU on mitigation of salt stress for the improvement of growth and development of a wheat genotype namely BARI Gom-30 and to reveal the physiological mechanisms of SA and TU for salt tolerance in wheat.

Methodology:

Plant materials and treatments: A wheat cultivar BARI Gom-30 (Triticum aestivum L.) was used as plant materials in this study. The hydroponic pot experiment was performed with two factorial arrangement of Salicylic Acid (SA) and Thiourea (TU) and salt treatments using a randomized complete block design (RCBD) with three replications. The salinity factor (NaCl) comprised of one level (150mM), and the SA and TU were applied at 150mM and 15mM levels, respectively. Therefore, the treatment combinations were as follows: ‘C’ 0 mM NaCl + 0 mM SA + 0mM TU (control); ‘S’ 150 mM NaCl + 0 mM SA/0mM TU; ‘S + SA’ 150 mM NaCl + 10 mM SA; ‘S + TU’ 150 mM NaCl + 15 mM TU; ‘S + SA + TU’ 150 mM NaCl + 10 mM SA+ 15 mM TU. Plant cultures and treatment induction: A homogenous lot of wheat seeds were separately surface sterilized by using 5% sodium hypochlorite + 2% Tween-20 for 25 min. Subsequently, presoaking of the seeds were done in dH₂O for 24 h and kept in a petridish with moistened filter paper for 3 days at room temperature (30°C) to induce germination and 20 seeds were placed per petridish. Evenly germinated seeds were placed in a Styrofoam seedling float (28 cm × 32 cm × 1.25cm) containing 60 (2×30) hole having nylon net at the bottom and fitted in a pot with 4L water capacity. Wheat seedlings were grown hydroponically using nutrient solution (Modified Cooper’s nutrient solution, Cooper, 1996). The control (T0) plants were grown on the nutrient solutions only with distilled water (dH20). After 7 days of seedling establishment in the pot, the salt treatment (T1, 150 mM NaCl) were applied in six steps employing 25mM in each pot in each time at an interval of 7 days (total six spray). The first and last salt stress imposition being on day 10th and day 42th, respectively. Simultaneously, the exogenous application of SA (T2, 10mM) and TU (T3, 15mM) were employed to the leaf surface of salt treated plants 20 days after seedling establishment (i.e. 10 days after stress imposition) individually to ensure the maximal penetration of externally applied compounds into the leaf tissues. The nutrient solutions were renewed at an interval of 15 days through the experimental period. Determination of photosynthetic pigments: Chlorophyll content (Chl a, Chl b, Total Chlorophyll content) and carotenoids were determined by randomly collected 42 days old leaf sample. An amount of 50 mg fresh leaf samples were taken into a small vial containing 10 ml of 80% acetone and was covered by aluminium foil and preserved in the dark for 7-10 days. The absorbance was measured at 663 nm for Chl a, 645 nm for Chl b and 663 nm wave length for total chlorophyll by using a spectrophotometer (Shimadzu UV-2550, Kyoto, Japan). Afterwards, the concentrations of Chl a, Chl b and total chlorophyll were calculated using the following formula: Chl a: 12.7(A663) – 2.69(A645); Chl b: 22.9(A645) – 4.68(A663) and total chlorophyll: 20.2(A645) + 8.02(A663) and expressed as μg g^-1 fresh weight (F.W.) of leaf. Measurement of leaf water related traits: Leaf water related traits viz., relative water content (RWC), relative water loss (RWL), and excised leaf water retention (ELWR) were determined according to Mostofa and Fujita (2013). In case of RWC measurement, leaf samples were collected after 42 days of planting and then weighed (FW) and immersed in dH₂O in a petridish for 4 hr. Subsequently, excess water was removed with a paper towel and turgid weight (TW) was immediately determined. After 48-hr oven-drying at 70 °C, dry weight (DW) was recorded, and leaf RWC was calculated according to the following formula: RWC (%) = FW − DW /TW − DW× 100. For the measurement of RWL, fresh weight (FW) of leaves were recorded and kept at 30ºC for 4 hours and reweighed (WW4h) and finally, oven dried at 72°C for 24 h to attain dry weight (DW). The RWL was measured according to the following formula: RWL (%) = [(FM – WW4h)/ (FW – DW)] × 100. For the measurement of ELWR, fresh weight (FW) of leaves were recorded and kept at 30ºC for 4 hours and reweighed (WW4h). Finally, ELWR was then calculated using the following formula: ELWR (%) = [1– (FW – WW4h)/ FW] ×100. Statistical analysis: Data were analyzed by Minitab 17 by a one way analysis of variance and significant differences between mean values with standard errors were presented indicated by different alphabetical letters in the same column at the p< 0.05 level using the least significant difference (LSD) test.

Source of Information: J Bangladesh Agril Univ 18(2): 272–282, 2020

Article Link (Online Journal): https://doi.org/10.5455/JBAU.86574

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The exposure of wheat seedlings to salt stress caused the severe reduction of growth parameters as well as photosynthetic pigments and leaf water status. The imposition of salt treatment lead the higher Na+/K+, H₂0₂ and MDA content in stressed wheat genotypes. In addition, the activities of different antioxidants were somewhat enhanced in the leaves of wheat seedlings under salt stress. On the other hand, the foliar spray of SA and TU greatly ameliorated the salt induced toxic effect and led the increment of growth parameters by the enhancement of photosynthetic attributes and by the prevention of electrolytic leakage in the leaves. Besides, SA and TU mediated effect lowered the Na+/K+ and protect the plant from oxidative damage by the maintenance of lower H₂O₂ and MDA content and by the up regulation of antioxidant enzymatic activities in salt stressed wheat seedlings.

Knowledge Management: Journal