Brassinosteroids And Humic Acid Alleviate Nanoplastic Toxicity In Edible Plants

The application of compost,plastic mulch and soil improver during the growing of food-derived plants inevitably leads to the release of nanoplastics into the soil.Nanoplastics can pose a threat to human health when transferred to edible parts of plants and absorbed in large quantities by plants.Currently,little is known about the accumulation of nanoplastics in edible parts of plants.The phytotoxicity caused by nanoplastics has attracted more and more attention,however,how to inhibit the absorption of nanoplastics by plants and reduce the subsequent adverse effects remains unclear.Here,the absorption and accumulation of polystyrene nanoplastics（PS-NPs）in different plants were studied,and the negative effects of PS-NPs on the growth of tomato seedlings and the induced oxidative damage were investigated with the model plant tomato.Brassinosteroids（BRs）and humic acid（HA）were also selected to treat tomatoes exposed to PS-NPs.The effects of BRs and HA on inhibiting the accumulation of PS-NPs and alleviating plant damage induced by PS-NPs were investigated by two ways of absorption,root or stoma,respectively.In order to provide reference for solving the problems of food safety and crop yield decrease caused by PS-NPs.The main research results are summarized as follows:（1）Accumulation and toxic effects of PS-NPs in edible parts of plants.The accumulation of PS-NPs in edible plants including tomato fruit,chili fruit,lettuce leaf,celery stem,coriander stem,tarragon stem,endive stem,scallion stem,spinach stem,and cabbage stem were studied.The results showed that the absorption of PS-NPs by different plants had similar laws.PS-NPs could be absorbed by plant roots and transported to edible parts through vascular bundle.Phytotoxicity induced by PS-NPs was studied in tomato.The results suggested that PS-NPs exposure concentration higher than 50 mg?L^-1had negative effects on plant growth,which significantly inhibited plant height,induced oxidative stress,and increased the levels of reactive oxygen species and lipid peroxidation in tomato seedlings.（2）The effect of brassinosteroids on inhibiting the accumulation of PS-NPs and alleviating phytotoxicity.In this study,tomatoes were exposed to 50 mg?L^-1PS-NPs and BRs were applied to inhibit PS-NPs accumulation and alleviate plant damage.The results showed that the application of 50 n M BRs significantly inhibited the accumulation of PS-NPs in tomato fruits.Compared with PS-NPs group,exogenous application of 50 n M BRs alleviated phytotoxicity and oxidative damage induced by PS-NPs,promoted plant growth,increased fresh weight and plant height.Besides,the expressions of aquaporin related genes such as TIP2-1,TIP2-2,PIP2-2,PIP2-8,PIP2-9,SIP2-1 and NIP1-2 were affected after the application of BRs.Transcriptome analysis showed that BRs enhanced the metabolism and synthesis of fatty acids and amino acids.Taken together,these results adequately indicated that BRs could mitigate PS-NPs toxicity in tomato.（3）The role of HA in alleviating the toxicity of PS-NPs.In this study,tomatoes were exposed to 50 mg?L^-1PS-NPs and HA were applied to inhibit PS-NPs accumulation and alleviate plant damage.The results showed that HA could significantly inhibit the accumulation of PS-NPs in tomato when the application concentration was higher than 50mg?L^-1.It might be achieved that HA induced stomatal closure by regulating the expression of genes related to stomatal development.Compared with PS-NPs group,50 mg?L^-1HA obviously increased plant fresh weight,alleviated phytotoxicity induced by PS-NPs,increased net photosynthetic rate,and promoted plant photosynthesis.It also alleviated oxidative stress,including the increase of reactive oxygen species and the aggravation of membrane lipid peroxidation caused by PS-NPs.These results indicated that HA could alleviate the adverse effects of PS-NPs on plants.