Arthrobacter pascens ZZ21 is a plant-beneficial, fluoranthene-degrading bacterial strain found in the rhizosphere. The production of the phytohormone indole-3-aectic acid (IAA) by ZZ21 is thought to contribute to its ability to promote plant growth and remediate fluoranthene-contaminated soil. Using genome-wide analysis combined with metabolomic and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses, we characterized the potential IAA biosynthesis pathways in A. pascens ZZ21. IAA production increased 4.5-fold in the presence of 200 mg·L⁻¹ tryptophan in the culture medium. The transcript levels of prr and aldH, genes which were predicted to encode aldehyde dehydrogenases, were significantly upregulated in response to exogenous tryptophan. Additionally, metabolomic analysis identified the intermediates indole-3-acetamide (IAM), indole-3-pyruvic acid (IPyA), and the enzymatic reduction product of the latter, indole-3-lactic acid (ILA), among the metabolites of ZZ21, and subsequently also IAM, ILA, and indole-3-ethanol (TOL), which is the enzymatic reduction product of indole-3-acetaldehyde, by HPLC-MS. These results suggest that the tryptophan-dependent IAM and IPyA pathways function in ZZ21.

The adverse effects of microplastics (MPs) and nanoplastics (NPs) on plant growth have gained significant attention. However, the response of tobacco plants to polypropylene microplastics (PP-MPs) remains poorly understood. To address this, a microcosm experiment was conducted in which tobacco seedlings were exposed to PP-MPs at varying concentrations (100 and 1000 mg/kg) and particle sizes (20 nm and 100 µm) for 48 days in red soil. The physicochemical, transcriptomic, and metabolic responses of tobacco plants to PP-MP treatments were assessed. Our findings indicate that the effect of PP-MP exposure on tobacco growth was dose-dependent, with the higher doses (1000 mg/kg) inducing significantly stronger responses. Further, a significant accumulation of key metabolites in the phenylpropanoid and flavonoid biosynthesis pathways such as quercetin, phloretin, kaempferol, liquiritigenin, naringin, myricetin, ferulic acid, formaldehyde, and methyl eugenol was observed in response to PP-MPs. Additionally, the transcriptomic analysis revealed that higher doses enriched more DEGs than lower. KEGG pathway analysis identified significant enrichment in phenylpropanoid biosynthesis, flavonoid biosynthesis, sesquiterpenoid and triterpenoid biosynthesis, and plant hormone signal transduction. The notable variation in the expression of key enzyme-related genes such as PAL, CHI, CSE, C4H, 4CL, COMT, and CYP indicates the substantial impact on lignin synthesis. Lastly, large-sized PPMPs alter the activity of key lignin-degrading enzymes, affecting the lignin content. This study offers valuable insights into the responses of tobacco plants to varying concentrations and sizes of PP-MPs, integrating both physicochemical and molecular perspectives.

The widespread use and degradation of agricultural plastics lead to the accumulation of nanoplastics (NPs) and soil contamination, posing growing risks to agroecosystems. This study investigated the differential physiological and molecular responses of maize (Zea mays) and soybean (Glycine max) to polyethylene nanoparticles (PE-NPs) and polypropylene nanoparticles (PP-NPs), each within the size range of 20-50 nm, at concentrations of 50 and 500 mg/kg of soil. Over a 45-day exposure period, at 500 mg/kg concentration, both NPs types significantly suppressed plant height and fresh biomass in both maize and soybean, with PP-NPs demonstrating greater toxicity in soybean than in maize. At 500 mg/kg, both crops accumulated high levels of both NPs types in their roots, triggering oxidative stress as evidenced by elevated malondialdehyde levels and a significant decline in catalase activity, which compromised root membrane integrity, antioxidant defense mechanisms, and nutrient availability. However, maize's higher photosynthetic efficiency, more vigorous root growth, and greater metabolic exudation made it more resilient to the NPs stress than soybean. To compare the molecular responses of maize and soybean, we conducted a multi-omics analysis of plants exposed to 500 mg/kg PP-NPs. The results showed a significant disruption of purine metabolism and phenylpropanoid biosynthesis in both plants, with the effect more pronounced in soybean. Soybean exhibited strong downregulation of adenosine deaminase and adenylate kinase, with reduced levels of xanthine, inosine, and uric acid. Notable alterations in the expression of key enzymes, such as phenylalanine ammonia-lyase, trans-cinnamate 4-monooxygenase, and peroxidase in both plants indicate a substantial impact on phenylpropanoid biosynthesis and its downstream flavonoid and lignin precursors. These findings reveal the distinct physiological and multi-omics responses underlying the resilience of maize and soybean to nanoplastic-contaminated soils.