Volume 15, Issue 1 (3-2024)                   2024, 15(1): 33-50 | Back to browse issues page


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Department of Plant Production and Genetics, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran.
Abstract:   (574 Views)
Abstract
Recently, with the rapid growth of industry and agriculture, the contamination of agricultural soils with the cadmium (Cd) and microplastic particles has become a serious issue. Simultaneous presence of microplastics and Cd in soil can cause various biological effects, especially in the early stages of plant growth. In this research, the effect of Cd stress in the presence of polyvinyl chloride (PVC) microplastic particles was investigated in the early stages of the growth of foxtail millet (Setaria italica L., cv. Bastan). The experiment was arranged in a factorial according to the completely randomized design with three replicates based on five concentrations of Cd (0, 50, 100, 150, and 200 µM) and PVC microplastic (0, 1, 2, 4, and 6%). The studied traits included percentage and inhibition of germination, rate and mean germination time, seedling vigor index, weight of mobilized seed reserve, seed reserve utilization efficiency, seed reserve depletion percentage, relative seed germination, seedling toxicity level, germination tolerance index and root tolerance index. The results showed that both pollutants led to the decrease of most germination indices, however, certain concentrations of PVC with Cd stress improved the desired indices. So that germination percentage and seed reserve utilization efficiency in 200 µM Cd concentration with 1% of PVC increased by 43.2 and 206%, respectively, compared to the concentration of 200 µM Cd alone. The highest inhibition of germination percentage belonged to 200 μM Cd concentration, which was reduced by 52.4% with the application of 1% microplastic. Although PVC microplastic particles had adverse effects on the germination process of foxtail millet seeds, but in the presence of Cd in the soil, low concentrations of PVC can have some moderating effects on Cd toxicity.

Background and Objective: Simultaneous contamination of soil with microplastics and heavy metals may pose a more severe threat to the soil and plants than the contamination of one of them alone (Wang et al., 2021). Due to their high adsorption capacity and carrier effect, microplastics can change the accessibility and toxicity of co-existing environmental pollutants in soil organisms and plants. Therefore, our objective was to investigate the possible effect of PVC and Cd on Cd toxicity, germination, and growth characteristics of seedlings. 

Methods: The factorial completely randomized design experiment with three replicates was conducted. The seeds disinfected with 5% hypochlorite were placed in a sterile petri dish with 20 ml of 0, 50, 100, 150, 200 µM Cd and 0, 1, 2, 4, and 6% PVC and were kept at 25°C for seven days. The seeds were counted once every 24 hours until the seventh day. Then, the root and shoot lengths were measured in centimeters. Each of the seedling parts was separated from each other, oven-dried at 70°C for 48 hours and weighed. Germination percentage, germination rate, seedling vigor index, mean germination time, weight of mobilized seed reserve, seed reserve utilization efficiency, seed reserve depletion percentage, root tolerance index, relative seed germination, germination tolerance index, seedling toxicity level and germination inhibition percentage were calculated. Data were analyzed through the SAS (v. 9.4) statistical program, and means values were compared by LSD test (p < 0.05).

Results: The effect of Cd and PVC on the examined traits was significant at the 1% probability level, except for the germination percentage, which was significant at the 5% probability level. The effect of Cd and PVC on the relative seed germination was not significant. The presence of PVC with Cd improved the percentage of germination, the mean germination time, and the seedling vigor index. The presence of microplastic decreased the adverse conditions of Cd stress and reduced the toxicity level and germination inhibition percentage. Heavy metals can be adsorbed by microplastic particles, which could reduce Cd adverse effects during germination (Yang et al., 2019). However, co-exposure of microplastic and Cd led to a decrease in germination rate. Duan et al. (2018) stated that the simultaneous presence of Cd and microplastic causes the accumulation of pollutants in plant cells and the intensification of oxidative stress, which leads to higher toxicity. The average germination time reduction in the presence of PVC under Cd stress. Due to the increased concentration of pollutants, disturbances were observed in the weight of mobilized seed reserve, seed reserve utilization efficiency, and seed reserve depletion percentage. Under the heavy metals stress, the starch mobility was reduced, and following the reduction of the mobility of seed reserves, the weight of the transferred seed reserves decreased (Seneviratne et al., 2019). Microplastics prevent water and nutrient absorption by the seeds, then delay germination and root growth (Bosker et al., 2019). The presence of microplastics moderated the adverse conditions of Cd stress and reduced the toxicity level, and germination inhibition percentage.

Conclusions: The PVC application moderated the Cd stress and improved the germination tolerance index as a crucial parameter of plant tolerance to stress. Therefore, despite the pollution of microplastic particles in the seed culture environment, our results demonstrated the reducing and balancing effects of PVC on Cd toxicity in foxtail millet seedlings, especially at low concentrations. However, this result needs more research, especially on other plants and in different concentrations of microplastics and Cd in different soils and it should not be considered as a positive effect of microplastics presence in the environment.

References:
1. Bosker, T., Bouwman, L.J., Brun, N.R., Behrens, P., Vijver, M.G., 2019. Microplastics accumulate on pores in seed capsule and delay germination and root growth of the terrestrial vascular plant Lepidium sativum. Chemosphere 226, 774781. https://doi.org/10.1016/j.chemosphere.2019.03.163
2. Duan, C., Fang, L., Yang, C., Chen, W., Cui, Y., Li, S., 2018. Reveal the response of enzyme activities to heavy metals through in situ zymography. Ecotoxicol. Environ. Saf. 156, 106115. https://doi.org/10.1016/j.ecoenv.2018.03.015
3. Seneviratne, M., Rajakaruna, N., Rizwan, M., Madawala, H.M.S.P., Ok, Y.S., Vithanage, M., 2019. Heavy metal-induced oxidative stress on seed germination and seedling development: a critical review. Environ. Geochem. Health 41(4), 18131831. https://doi.org/10.1007/s10653-017-0005-8
4. Wang, F., Wang, X., Song, N., 2021. Polyethylene microplastics increase cadmium uptake in lettuce (Lactuca sativa L.) by altering the soil microenvironment. Sci. Total Environ. 784, 147133. https://doi.org/10.1016/j.scitotenv.2021.147133
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Type of Study: Research | Subject: Plant growth under stressful conditions
Received: 2023/11/15 | Accepted: 2024/02/4 | Published: 2024/06/18

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