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Aluminium Toxicity on the Activities of Antioxidant Enzymes in Rice (oryza Sativa L.) and Chickpea (cicer Arietinum L.) Seedlings Grown in Hydroponic Culture

Rifat Samad
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Parveen Rashid
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

JL Karmoker
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

Effects of four different concentrations of aluminum (10, 50, 100 and 150 µM) on some antioxidant enzyme activities like peroxidase, catalase and superoxide dismutase of the seedlings of rice and chickpea grown in hydroponic culture showed aluminium toxicity which caused a dramatic increase in peroxidase and catalase activities in the root and shoot of rice seedlings. Al (150 µM) caused an eight to nine-fold increase in peroxidase and catalase activity, respectively, in the root of rice seedlings. On the contrary, Al stress decreased superoxide dismutase (SOD) activity in the root and shoot of rice seedlings. In chickpea seedlings, Al stress caused a few-fold increase in peroxidase, catalase and SOD activities in the roots and leaves. A dramatic 14.8 and 14.6-folds increase in SOD activity was recorded in the roots and leaves of chickpea seedlings, respectively. It is noted that there is a generic difference between rice and chickpea with respect to the effect of Al stress on SOD activity.

Keywords: Aluminium toxicity, Antioxidant enzymes, Superoxide dismutase, Rice, Chickpea

Location: Department of Botany, University of Dhaka, Dhaka, Bangladesh.

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Rice, Chickpea

Objectives:

To investigate the effect of aluminum toxicity on the activities of peroxidase, catalase and superoxide dismutase of rice and chickpea seedlings grown in hydroponic culture.

Methodology:

Rice (Oryza sativa L. var. BRRI Dhan-53), the most widely consumed cereal grain of the family Poaceae and chickpea (Cicer arietinum L. var. BARI chhola-7), the third most extensively planted grain legume of the family Fabaceae were used as experimental plant materials. Seeds of rice were collected from Bangladesh Rice Research Institute (BRRI) and that of chickpea were procured from Bangladesh Agricultural Research Institute (BARI). The experiments were conducted at the Department of Botany, University of Dhaka, Dhaka, Bangladesh. The seeds were surface-sterilized according to Samad and Karmoker (2013). The sterilized seeds were spread over a cotton gauge placed in a lid having holes (1 cm in diameter) and the lid with seeds was placed on a beaker containing 500 ml of distilled water. The beakers were covered by a black plastic sheet to avoid the exposure of light to the roots. After germination, the seedlings were transferred to a modified half-strength Hoagland solution (Hoagland and Arnon 1950) and the beakers with the seedlings were placed in a light bank. Rice seedlings were grown at a day/night temperature of 30 ± 1^oC/25 ± 1^oC and day/night length of 14 hrs/10 hrs. Chickpea seedlings were grown at a day/night temperature of 25 ± 1^oC/18 ± 1^oC and day/night length of 10 hrs/14 hrs. Light intensity was 160 µ-einstein/m²s. The solution was continuously aerated through a bubbler with the help of an air compressor (Rockyvac 320). The solution was replenished every 48 hrs. Seven-day-old seedlings were transferred to half-strength Hoagland solution as control and 10, 50, 100 and 150 µM AlCl₃ solution made in half-strength Hoagland solution were used as treatments. The pH of all solutions including control was adjusted to 4.2 with 0.2N H₂SO₄. For the determination of the activities of antioxidant enzymes, 0.5 g of plant sample was homogenized in 0.05 M phosphate buffer (pH 7.8). Homogenate was centrifuged at 10,000 rpm for 10 min at 4ºC. The supernatant was separated and used for specific enzyme assay. The activity of peroxidase was determined by the method as described by Zhang et al. (1995). The reaction mixture consisted of 0.1 M phosphate buffer (pH 7.8), 30% H₂O₂ and 0.05 M guaiacol (freshly prepared). The supernatant (0.2) ml was added to the reaction mixture. The change of optical density (O.D) was measured at a wavelength of 470 nm with a spectrophotometer every 30 sec for 2 min. Peroxidase activity was expressed as µmol/min/mg/ protein. The catalase activity was assayed according to the method of Barber (1980). Catalase activity was measured by using an assay solution containing 0.05 M phosphate buffer (pH 7.8), 0.1 M H₂O₂ and 0.2 ml extract. A decrease in absorbance of H₂O₂ was recorded within 2 min at 240 nm. One unit of catalase activity was defined as the amount of enzyme required to reduce 1 μmol of H₂O₂ per min. Catalase activity was expressed as µmol/min/mg/protein. The superoxide dismutase (SOD) activity was determined according to the modified method of Zhang et al. (2005). The SOD activity was determined by measuring the inhibition of the photochemical reduction of nitroblue tetrazolium chloride (NBT). The reagents used for assay included 50 mM phosphate buffer (pH 7.8), 130 mmol/l methionine, 750 µmol/l NBT, 100 µmol/l Na₂-EDTA and 20 µmol/l riboflavin. After adding 1 ml of supernatant (extract) to the reaction mixture, the test tubes were exposed for 10 mins to fluorescent light (13 W). Then the change in absorbance was followed up to 2 min at a wavelength of 560 nm using a spectrophotometer (Shimadzu, Model: UV-1800, Japan). One unit of SOD was defined as the amount of enzyme required to inhibit NBT reduction by 50% under specified conditions of the assay. SOD activity was expressed as unit min/mg/protein.

Source of Information: Bangladesh J. Bot. 49(3): 619-624, 2020 (September)

Article Link (Online Journal): DOI: https://doi.org/10.3329/bjb.v49i3.49994

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Antioxidant enzyme activities serve as a key biochemical indicator to assess the sensitivity of plants under stress conditions. Al triggers increased production of ROS which includes singlet oxygen (0.5 O₂), superoxide radical (O₂), hydroxyl radical (OH) and H₂O₂ in the tissue. ROS causes damage to lipid, protein and nucleic acid in the cells. The most effective antioxidant enzyme preventing ROS-induced cellular oxidative damage is SOD which catalyzes the conversion of 0.5 O₂ ? to H₂O₂ whereas catalase scavenges H₂O₂ and peroxidase use H₂O₂ for oxidation of various organic substrates. Thus, Al-induced increase in activities of antioxidant enzymes peroxidase, catalase and SOD play a vital role in the tolerance of plants under Al-stress.

Knowledge Management: Journal