Titanium dioxide nanoparticles (TiO2 NPs) have been widely used in agriculture, which increased the risk to soilplant systems. Studies have demonstrated that TiO2 NPs can induce phytotoxicity. However, the toxicity mechanisms, particularly under the stress of TiO2 NPs with different crystalline forms, remain inadequately reported. In this study, we combined transcriptomics and metabolomics to analyze the toxicity mechanisms in rice (Oryza sativa L.) under the stress of anatase (AT) or rutile (RT) TiO2 NPs (50 mg/kg, 40 days). The length (decreased by 1.1-fold, p = 0.021) and malondialdehyde concentration (decreased by 1.4-fold, p = 0.0027) of rice shoots was significantly reduced after AT exposure, while no significant changes were observed following RT exposure. Antioxidant enzyme activities were significantly altered both in the AT and RT groups, indicating TiO2 NPs induced rice oxidative damage (with changes of 1.1 to 1.4-fold, p < 0.05). Additionally, compared to the control, AT exposure altered 3247 differentially expressed genes (DEGs) and 56 significantly differentially metabolites in rice (collectively involved in pyrimidine metabolism, TCA cycle, fatty acid metabolism, and amino acid metabolism). After RT exposure, 2814 DEGs and 55 significantly differentially metabolites were identified, which were collectively involved in fatty acid metabolism and amino acid metabolism. Our results indicated that AT exposure led to more pronounced changes in biological responses related to oxidative stress and had more negative effects on rice growth compared to RT exposure. These findings provide new insights into the phytotoxic mechanisms of TiO2 NPs with different crystalline forms. Based on the observed adverse effects, the study emphasizes that any form of TiO2 NPs should be used with caution in rice ecosystems. This study is the first to demonstrate that AT is more toxic than RT in paddy ecosystems, providing crucial insights into the differential impacts and toxic mechanisms of TiO2 NPs with different crystalline forms. These findings suggest prioritizing the use of RT when TiO2 NPs are necessary in agricultural development to minimize toxicity risks.

Polyethylene microplastics (PE-MPs) have toxicity to ecological environment, including animals and plants. This study investigated the toxicity of photodegraded PE-MPs on Brassica rapa, which is a typical model plant and only have around a 30-day life cycle. It is noted that the presence of photodegraded PEMPs inhibited Brassica rapa growth since the stem length decreased by 11.94%-51.11 % while the fresh weight and dry weight decreased by 18.56%-27.46 % and 1.90 %-6.91 % respectively, compared to the blank group. PE-MPs receiving more light radiation became more hydrophobic. This inhibited PE-MPs entering the plant body along with the process of plant absorbing water. Furthermore, when PE-MPs were located in the lower soil layers, Brassica rapa reaching them needs a longer time, hence showing lower toxicity effect than the case of PE-MPs located in the upper soil layer. The research outcomes also indicated that malondialdehyde (MDA) contents in photodegraded PE-MPs exposure group increased by 1.37%-7.28 % while the catalase activity (CAT) increased by 60.11 %. This means that PE-MPs caused oxidative stress response in plants, inducing plants to resist external stress. Transcriptomic analysis results showed that Brassica rapa, which was affected by PE-MPs, significantly up-regulated genes related to the plant-pathogen interaction pathway while the ribosome pathway genes were significantly downregulated. This led to a decrease in growth rate and a decrease in the homeostatic level of the ribosomal subunit and hence resulting in abnormal leaf vein development. These conclusions indicated the toxic effect and damage mechanism of photodegraded PE-MPs on Brassica rapa. The novelty of this study was to use both univariate analysis and transcriptomic analysis to investigate how photodegraded PE-MPs exert toxicity on Brassica rapa. The results can provide a theoretical basis for revealing the influence of MPs on plant growth. (c) 2024 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).