Document Type : Research Article
Authors
1
2Department of Biology, College of Science, Shiraz University, Shiraz, Iran
2
Department of Biology, College of Science, Shiraz University, Shiraz, Iran
10.22067/jpp.2025.92623.1224
Abstract
Introduction
Microplastic pollution has become a growing environmental concern, with polyethylene (PE) being one of the most prevalent sources. These plastic particles, originating from industrial activities, plastic degradation, and agricultural applications, persist in ecosystems and pose significant threats to plant growth, soil health, and overall agricultural productivity. Recent studies have highlighted the widespread contamination of microplastics in terrestrial and aquatic environments, raising concerns about their impact on plant physiology and development. Polyethylene microplastics (PE-MPs) are widely used in agricultural plastic mulch, greenhouse films, and packaging materials. Over time, these plastics degrade into micro-sized fragments that infiltrate the soil, potentially altering soil properties, affecting microbial communities, and influencing plant growth. Despite the increasing awareness of microplastic contamination, limited studies have been conducted to elucidate the effects of PE-MPs on economically important crops such as wheat (Triticum aestivum L.). Wheat is a staple food crop cultivated worldwide, and any factor affecting its growth and productivity could have severe implications for food security. This study aims to investigate the physiological and biochemical effects of PE-MPs on wheat seed germination and seedling development. Key parameters such as germination rate, shoot and root growth, biomass allocation, photosynthetic pigment content, and proline accumulation are examined to provide a comprehensive understanding of the impact of microplastic pollution on crop health. The results of this study will contribute to the ongoing discussion regarding the environmental risks of microplastic pollution and the need for sustainable agricultural practices.
Materials and Methods
This study was conducted under controlled greenhouse conditions using a completely randomized design. The experiment involved four different concentrations of polyethylene microplastics: 0 mg/L (control), 1 mg/L, 10 mg/L, and 100 mg/L, with four replications per treatment group. Wheat seeds (Triticum aestivum L.) were sterilized with sodium hypochlorite (5%) and washed with distilled water before sowing. The seeds were placed in pots filled with perlite, and Hoagland's nutrient solution was applied regularly to ensure adequate nutrition. After one week of germination, polyethylene microplastics were introduced into the growth medium. The plants were grown under optimal temperature and light conditions for two additional weeks before harvesting. To assess the impact of PE-MPs on wheat seedlings, several physiological and biochemical parameters were measured: Germination rate: The percentage of seeds that successfully germinated under different PE-MP concentrations. Shoot and root growth: Length measurements of shoots and roots were recorded using a ruler. Biomass allocation: Fresh and dry weights of shoots and roots were measured to determine any changes in biomass distribution. Chlorophyll and carotenoid content: Spectrophotometric analysis was performed using the Arnon method to quantify chlorophyll a, chlorophyll b, and total carotenoids. Proline content: The acid ninhydrin method was employed to determine the accumulation of proline, an indicator of oxidative stress and plant defense responses.
Results
The results demonstrated that polyethylene microplastics had concentration-dependent effects on wheat seed germination and seedling growth. Germination: While the lowest concentration (1 mg/L) of PE-MPs had no significant impact on germination rate, moderate (10 mg/L) and high (100 mg/L) concentrations significantly reduced germination percentages. The inhibitory effect at higher concentrations suggests that microplastic exposure interferes with water uptake and seed metabolism. Root and shoot growth: Root length exhibited a notable increase across all treatment levels, with the highest stimulation observed at 10 mg/L. In contrast, shoot growth was negatively affected at both moderate and high concentrations, indicating an asymmetric response of different plant organs to PE-MP exposure. Biomass distribution: Root biomass increased significantly at 10 mg/L and 100 mg/L, while shoot biomass declined. This suggests that wheat seedlings may redirect energy allocation towards root development to enhance water and nutrient uptake under stress conditions. Photosynthetic pigments: Chlorophyll and carotenoid levels showed a biphasic response. At 1 mg/L and 10 mg/L, an increase in pigment concentration was observed, possibly due to a hormetic response where low levels of stress stimulate plant defense mechanisms. However, at 100 mg/L, both chlorophyll and carotenoid contents decreased, indicating oxidative stress and potential chloroplast damage. Proline accumulation: Proline content progressively increased with rising PE-MP concentrations. This suggests that polyethylene microplastics induce osmotic stress, triggering proline biosynthesis as a protective mechanism against oxidative damage.
Discussion
The observed results indicate that polyethylene microplastics have complex and concentration-dependent effects on wheat growth. The increase in root length and biomass at higher concentrations suggests an adaptive response, where plants prioritize root expansion to improve nutrient acquisition under stress conditions. However, the simultaneous decline in shoot growth, germination rate, and photosynthetic pigments at higher microplastic levels highlights the detrimental consequences of microplastic pollution on crop physiology. The decrease in chlorophyll and carotenoid content at high PE-MP concentrations aligns with previous studies reporting microplastic-induced oxidative stress. Reduced photosynthetic efficiency can directly impact crop productivity and grain yield, raising concerns about the long-term implications of microplastic contamination in agricultural soils. Proline accumulation serves as an important biomarker for plant stress tolerance. The significant increase in proline levels at higher PE-MP concentrations suggests that wheat seedlings perceive microplastics as an abiotic stress factor. Proline plays a crucial role in stabilizing cellular structures, scavenging reactive oxygen species (ROS), and maintaining osmotic balance under stress conditions.
Conclusion
This study highlights the potential risks of polyethylene microplastic pollution on wheat growth and development. While low concentrations of PE-MPs may induce mild stimulatory effects on certain physiological parameters, higher concentrations negatively impact germination, shoot growth, and photosynthetic efficiency, while triggering stress-related responses such as proline accumulation. These findings emphasize the urgent need for policies and practices that mitigate microplastic pollution in agricultural soils. Future research should explore the long-term effects of microplastics on soil health, crop productivity, and food safety to ensure sustainable agricultural production in the face of increasing environmental pollution.
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