| چکیده انگلیسی مقاله |
Silica nanoparticles can reduce the adverse effects of abiotic stresses by modulating several physiological processes. However, there is little information about how these effects are mediated under heavy metal stress. This study investigated the role of silicon nanoparticles in mitigating the toxicity of cadmium chloride in tomatoes (Solanum lycopersicum L.) was investigated. Silicon nanoparticles were used at levels 0, 25, 50, and 100 mg/l, and cadmium chloride at three levels of 0, 100, and 200 µM. The results showed that 200 μM cadmium treatment resulted in a decrease in plant fresh weight and length, ascorbate and glutathione levels in shoots and roots, but increased cadmium, malondialdehyde, H2O2, and protein content compared to the level 0 cadmium treatment. 50 mg/l nanosilica treatment resulted in an increase in plant fresh weight and length, an increase in ascorbate and glutathione levels, and a decrease in cadmium, malondialdehyde, H2O2, and protein content compared to the level 0 nanosilica treatment. Cadmium stress increased the activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase, and glutathione-S-transferase, and the treatment of 50 mg/l silicon nanoparticles under cadmium stress enhanced the activity of these enzymes. The maximum increase in the activity of enzymes by silicon nanoparticles showed that these nanoparticles play a significant role in detoxifying reactive oxygen species and reducing oxidative stress induced by cadmium.
Introduction
Environmental pollution by heavy metals has become a serious concern. Plants more readily take up Cadmium (Cd) than other heavy metals due to their high mobility and good water solubility. The high toxicity of Cd in plants may threaten crop quality and yield. Cd induces the production of reactive oxygen species (ROS). The tripeptide glutathione (Glu-Cys-Gly), widely synthesized in plants, contains a sulfhydryl group and can quench ROS. The reduced glutathione (GSH) pool is maintained by glutathione reductase (GR), which catalyzes the NADPH-dependent reduction of the disulfide bond in the glutathione molecule. Silica (Si) is the most abundant non-metallic element in the Earth's crust after oxygen. Most plants absorb soil-soluble Si from mineral sources such as silicic or monosilicic acid. Tomatoes, one of the most popular and widely consumed crops worldwide, are significant for employing strategies to mitigate the effects of toxic substances such as Cd, thereby enhancing product quality. In this context, Alves et al. (2020) used selenium, and Naciri et al. (2021) used potassium to alleviate Cd stress in tomatoes. However, available information on the effects of Nano-SiO2 under stress conditions is limited. Therefore, this study aims to investigate how Nano-SiO2 relieves Cd stress at the morphological, biochemical, and enzymatic levels.
Materials and Methods
This research was conducted as a factorial experiment in triplicate, based on a completely randomized design at Urmia University. Tomato seeds purchased from Glass Garden Company were surface sterilized using 0.1% sodium hypochlorite for 15 min, rinsed, and cultured in Petri dishes. Three days after germination, the seedlings were transferred to pots containing perlite, and a half-strength micronutrient solution of Hoagland was used for irrigation and nutrition. The plants were maintained in a greenhouse with 16 hr of light and 8 hr of darkness at a temperature of 25°C during the day and 20°C at night, with a relative humidity of 70%. Nano-SiO2 was prepared at 0, 25, 50, and 100 mg/l concentrations and sonicated for 45 min. Immediately after sonication, the plants were sprayed with Nano-SiO2 once a day during the four-leaf stage for four days. Following the Nano-SiO2 treatment, the seedlings were irrigated with Hoagland solution containing CdCl2 at concentrations of 0, 100, and 200 μM for seven days. Finally, the shoots and roots were separated, frozen in liquid nitrogen, and stored at -80 °C for subsequent experiments. Malondialdehyde (MDA), hydrogen peroxide (H2O2), ascorbic acid (ASA), and dehydroascorbate (DHA) reduced glutathione (GSH (and oxidized glutathione (GSSG) levels were determined. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), GR, and glutathione-S-transferase (GST) enzymes were also measured. All treatments were performed in triplicate, and the results were presented as mean ± SD (standard deviation). Statistical differences were evaluated using Microsoft Excel and Two Way ANOVA, followed by Duncan's multiple range test. P < 0.05 was considered to indicate a significant difference.
Results and discussion
The results showed that 200 μM CdCl2 decreased plant fresh weight and length, reduced ascorbate and glutathione content, and increased levels of Cd, MDA, and H2O2 compared to the 0 CdCl2 treatment. In contrast, the 50 mg/l Nano-SiO2 treatment increased plant fresh weight and length, elevated ascorbate and glutathione content, and decreased Cd, MDA, and H2O2 levels compared to the 0 Nano-SiO2 treatment. Furthermore, 200 μM CdCl2 increased protein content and antioxidant enzyme activity compared to the 0 CdCl2 treatment. The increase in antioxidant enzyme activity observed in this study under Cd stress suggests that this activity may not effectively neutralize ROS in tomatoes, as indicated by the elevated levels of MDA and H2O2. The content of MDA and H2O2 remained high despite the increase in antioxidant enzyme activity, suggesting that H2O2 accumulation exceeded the ROS scavenging capacity of the plants under Cd stress, resulting in oxidative stress due to an imbalance between ROS production and removal. However, the treatment with 50 mg/l Nano-SiO2 under 200 μM CdCl2 further increased antioxidant enzyme activity. This suggests that by enhancing antioxidant enzyme activity, Nano-SiO2 significantly reduces MDA and H2O2 levels, contributing to the stability of cell membranes and creating an environment with lower oxidative stress, as reflected in the reduction of lipid peroxidation. Consequently, these factors improve growth and increase tomato biomass under Cd stress.
Conclusion
The findings of this study indicate that spraying 50 mg/l of Nano-SiO2 is an effective method for enhancing tomato growth under Cd stress, as it stimulates antioxidant enzyme activity and reduces oxidative stress. Additionally, Nano-SiO2 can serve as a viable source for producing safe food products in response to food security challenges, particularly in lands contaminated with the heavy metal Cd. This method presents a suitable alternative to traditional approaches. However, field-scale studies are needed to understand these results better and confirm them. |