Dual pathways of photosynthetic inhibition by nanoplastics: Light reaction blockade in soybean and carbon fixation enzyme suppression in corn

Nanoplastics (NPs) have raised increasing attention due to their potential environmental risks to terrestrial vegetation and food security. However, for the plants with various photosynthetic pathways, the differences in their photosynthetic response and related mechanisms upon NPs exposure are still unclear. Here, the photosynthetic responses of typical soybean and corn plants under polystyrene NPs (PSNPs) exposure were systematically compared for the first time. Our results revealed that the uptake of PSNPs by soybean and corn roots and was efficiently transferred to plant aerial portion through vascular bundle. The net photosynthetic rate of corn and soybean seedlings decreased 13.22 %-42.98 % and 17.28 %-48.19 % respectively, within different concentrations of PSNPs. For soybean plants, PSNPs hindered the photosynthesis in soybean by reducing the chlorophyll content, inhibiting the energy conversion efficiency of PSII and blocking electron transport in the light reaction. But for corn plants, the relative expression of carbon fixation enzyme genes (pepc, rbcL and rbcS) encoding phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were down-regulated in corn exposed to PSNPs, and the activity of PEPC and Rubisco were significantly decreased by 21.54 %-30.77 % and 9.38 %-18.75 % respectively. The study highlighted PSNPs induce stronger soybean plants stress than corn plants responses from photosynthesis perspectives, which are valuable for evaluating the potential risks of NPs to food security of crops with different photosynthetic pathways.