Optimistic effects of galaxolide and polystyrene microplastic stress on the physio-biochemical characteristics and metabolic profiles of an ornamental plant

Galaxolide (HHCB) and polystyrene (PS) microplastics or nanoplastics have been widely recognized as emerging pollutants. However, very few efforts have been made to remove these contaminants from the environment using eco-friendly materials such as plant materials. Therefore, this study sought to investigate the physiological and biochemical effects and tolerance mechanisms of Mirabilis jalapa L. upon exposure to HHCB and PS. Our findings demonstrated that this ornamental plant was tolerant to HHCB and PS exposure. HHCB treatment increased antioxidant enzyme activity. However, superoxide dismutase (SOD) activity increased by 206.85% when the plants were treated with 0.5 mg L HHCB alone, whereas co-exposure to 0.5 mg L HHCB and 500 nm PS increased SOD activity by 93.82%. Contaminant exposure also affected photosynthetic parameters such as stomatal conductance and transpiration rate. In contrast, net photosynthetic rate and photosynthetic pigment content were not significantly affected. HHCB aggregated heavily in the roots of the plant. Moreover, 500 nm PS could be absorbed by the root and transported to the shoot, and 5 μm PS would be transferred to the shoot under the carrying effect of HHCB. Co-exposure to HHCB and PS significantly changed the glyoxylate and dicarboxylate metabolism, alanine, aspartate, and glutamate metabolism, and glycine, serine, and threonine metabolism pathways, thus affecting carbohydrate synthesis and energy metabolism in M. jalapa. These results provide a basis for the development of HHCB and PS remediation strategies using M. jalapa, an ornamental plant that is not only tolerant to organic contaminants but can also beautify the environment.