Reducing phenanthrene uptake and translocation, and accumulation in the seeds by overexpressing OsNRT2.3b in rice

Endogenous IAA affected fluoranthene accumulation by regulating H+-ATPase and SOD activity in ryegrass

This study explores the role of endogenous indole-3-acetic acid (IAA) in modulating plant responses to pollution stress and its effect on pollutant accumulation, with a focus on fluoranthene (Flu) in ryegrass. To elucidate the mechanism, we employed an IAA promoter (α-aminobutyric acid [α-AB]) and an IAA inhibitor (naphthylphthalamic acid [NPA]) to regulate IAA levels and analyze Flu uptake characteristics. The experimental setup included a Flu treatment group (ryegrass with Flu addition) and a control group (ryegrass without Flu). Our findings demonstrate that Flu treatment enhanced IAA content and plant growth in ryegrass compared to the control. The Flu+AB treatment further enhanced these effects, while the Flu+NPA treatment exhibited a contrasting trend. Moreover, Flu+AB treatment led to increased Flu accumulation, in contrast to the inhibitory effect observed with Flu+NPA treatment. Flu treatment also enhanced the activities of key antioxidant enzymes (SOD, POD, CAT) and increased soluble sugar and protein levels, indicative of enzymatic and nonenzymatic defense responses, respectively. The Flu+AB treatment amplified these responses, whereas the Flu+NPA treatment attenuated them. Significantly, Flu treatment raised H+-ATPase activity compared to the control, an effect further elevated by Flu+AB treatment and diminished by Flu+NPA treatment. A random forest analysis suggested that Flu accumulation dependency varied under different treatments: it relied more on H+-ATPase activity under Flu+AB treatment and more on SOD activity under Flu+NPA treatment. Additionally, Flu+AB treatment boosted the transpiration rate in ryegrass, thereby increasing the Flu translocation factor, a trend reversed by Flu+NPA treatment. This research highlights crucial factors influencing Flu accumulation in ryegrass, offering potential new avenues for controlling the gathering of contaminants within plant systems.

A new strategy of using periphyton to simultaneously promote remediation of PAHs-contaminated soil and production of safer crops

Contaminated farmland leads to serious problems for human health through biomagnification in the soil-crop-human chain. In this paper, we have established a new soil remediation strategy using periphyton for the production of safer rice. Four representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (Phe), pyrene (Pyr), benzo[b]fluoranthene (BbF), and benzo[a]pyrene (BaP), were chosen to generate artificially contaminated soil. Pot experiments demonstrated that in comparison with rice cultivation in polluted soil with ΣPAHs (50 mg kg-1) but without periphyton, adding periphyton decreased ΣPAHs contents in both rice roots and shoots by 98.98% and 99.76%, respectively, and soil ΣPAHs removal reached 94.19%. Subsequently, risk assessment of ΣPAHs based on toxic equivalent concentration (TEQ), pollution load index (PLI), hazard index (HI), toxic unit for PAHs mixture (TUm), and incremental lifetime cancer risk (ILCR) indicated that periphyton lowered the ecological and carcinogenicity risks of PAHs. Besides, the role of periphyton in enhancing the rice productivity was revealed. The results indicated that periphyton alleviated the oxidative stress of PAHs on rice by reducing malondialdehyde (MDA) content and increasing total antioxidant capacity (T-AOC). Periphyton reduced the toxic stress of PAHs on the soil by promoting soil carbon cycling and metabolic activities as well. Periphyton also improved the soil's physicochemical properties, such as the percentage of soil aggregate, the contents of humic substances (HSs) and nutrients, which increased rice biomass. These findings confirmed that periphyton could improve rice productivity by enhancing soil quality and health. This study provides a new eco-friendly strategy for soil remediation and simultaneously enables the production of safe crops on contaminated land.

Mechanism and Association between Microbial Nitrogen Transformation in Rhizosphere and Accumulation of Ciprofloxacin in Choysum (Brassica parachinensis)

Rhizosphere microbiota are an important factor impacting plant uptake of pollutants. However, little is known about how microbial nitrogen (N) transformation in the rhizosphere affects the uptake and accumulation of antibiotics in plants. Here, we determined recruitment of N transformation functional bacteria upon ciprofloxacin (CIP) exposure, by comparing differences in assembly processes of both rhizospheric bacterial communities and N transformation between two choysum (Brassica parachinensis) varieties differing in CIP accumulation. The low accumulation variety (LAV) of CIP recruited more host bacteria (e.g., Nitrospiria and Nitrolancea) carrying nitrification genes (mainly nxrA) but fewer host bacteria carrying denitrification genes, especially narG, relative to the high accumulation variety (HAV) of CIP. The nxrA and narG abundance in the LAV rhizosphere were, respectively, 1.6-7.8 fold higher and 1.4-3.4 fold lower than those in the HAV rhizosphere. Considering that nitrate can decrease CIP uptake into choysum through competing for the proton motive force and energy, such specific bacteria recruitment in LAV favored the production and utilization of nitrate in its rhizosphere, thus limiting its CIP accumulation with 1.6-2.4 fold lower than the HAV. The findings give insight into the mechanism underlying low pollutant accumulation, filling the knowledge gap regarding the profound effects of rhizosphere microflora and N transformation processes on antibiotic accumulation in crops.

Concentration-dependent mechanisms of fluoranthene uptake by ryegrass

Fluoranthene (Flu) uptake by plants is affected by plant growth and environmental concentration. Although plant growth processes, including substance synthesis and antioxidant enzyme activities, have been reported to regulate Flu uptake, their contributions have been poorly evaluated. Moreover, the effect of Flu concentration is little known. Here, low concentrations (0, 1, 5, and 10 mg/L) and high concentrations (20, 30, and 40 mg/L) of Flu were set to compare the changes in Flu uptake by ryegrass (Lolium multiflorum Lam.). Indices of plant growth (biomass, root length, root area, root tip number, and photosynthesis and transpiration rates), substance synthesis (indole acetic acid [IAA] content), and antioxidant enzyme activities (superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT]) were recorded to unravel the mechanism of Flu uptake. Findings suggested that the Langmuir model fitted Flu uptake by ryegrass well. Flu absorption capacity in the root was stronger than that that in the leaf. Flu bioconcentration and translocation factors increased then reduced with the increase in Flu concentration and reached the maximum value under 5 mg/L Flu treatment. Plant growth and IAA content had the same pattern as before bioconcentration factor (BCF). SOD and POD activities increased then decreased with Flu concentration and reached their highest levels under 30 and 20 mg/L Flu treatments, respectively, whereas CAT activity decreased continuously and reached its lowest level under 40 mg/L Flu treatment. Variance partitioning analysis indicated that IAA content had the greatest significant effect on Flu uptake under low-concentration Flu treatments, whereas antioxidant enzyme activities had the greatest significant effect on Flu uptake under high-concentration Flu treatments. Revealing the concentration-dependent mechanisms of Flu uptake could provide a basis for regulating pollutant accumulation in plants.

The association between phenanthrene and nutrients uptake in lotus cultivar 'Zhongguo Hong Beijing'

It has been well documented that polycyclic aromatic hydrocarbon (PAHs) can be taken up from the environment by the plants and translocated into the shoots. However, the mechanisms underlying this process are poorly understood. Nelumbo nucifera L. (lotus) is a highly ornamental aquatic plant known to possess strong phytoremediation capability. In the present study, the association between phenanthrene (Phe) and nutrients, including nitrogen (N) and phosphorus (P), in lotus was investigated. Over 2 years, all eight lotus cultivars tested accumulated Phe to various degrees when grown in PAH-polluted sediment (0.46 mg/kg Phe). Cluster analysis showed N. nucifera 'Zhongguo Hong Beijing (ZHB)' was the one with the highest Phe levels in the leaves and petals in 2 years. The Phe concentrations in the tissues of 'ZHB' were 3.14 mg/kg and 1.63 mg/kg on average in the first and second year, respectively. Interestingly, 'ZHB' was also the cultivar with the lowest N and P levels considering 2 years and tissues. Hydroponic studies further revealed a negative association between the concentrations of Phe and those of N and P in the aerial tissues under 0.5 and 1.0 mg/L Phe treatments in 'ZHB'. Furthermore, the significant reductions of the roots number (72.6%), longest root length (75.8%), and petiolar height (34.6%) in 'ZHB' seedlings exposed to 1.0 mg/L Phe were observed, indicating that Phe retarded the growth of lotus. These results provide a new understanding of the accumulation of Phe in plants and the association with nutrients and enrich the basis of phytoremediation to the contaminated environment.

Distribution of phenanthrene in the ospho2 reveals the involvement of phosphate on phenanthrene translocation and accumulation in rice

The intricate mechanisms involved in the acquisition and translocation of polycyclic aromatic hydrocarbons (PAHs) in plants have not been elucidated. Phosphate (Pi) is the bioavailable form of essential macronutrient phosphorus, which is acquired and subsequently assimilated for plant optimal growth and development. Rice phosphate overaccumulator 2 (OsPHO2) is a central constituent of the regulation of Pi homeostasis in rice. In the present study, the role of OsPHO2 in regulating the translocation and accumulation of phenanthrene (Phe) and the involvement of Pi in this process were investigated. The temporal study (1 d-35 d) revealed a significant and gradual increase of Phe accumulation in Pi-deprived roots of wild-type (WT) seedlings. Compared with the WT, the concentrations of Phe were significantly higher in the shoots of ospho2 (OsPHO2 mutant) grown hydroponically with Phe (1.5 mg/L) under +Pi (200 μM) and -Pi (10 μM) conditions. The sap experiment clearly showed the significant increases in levels of Phe in the xylem sap of ospho2 than the WT grown hydroponically with Phe and +Pi. Further, the concentrations of both Phe and P were coordinately higher in the culms and flag leaves of the mutants than WT at maturity in potting soil with LPhe (6 mg/kg) and HPhe (60 mg/kg). However, the concentrations of Phe in the seeds were comparable in the WT and mutants, suggesting a pivotal of OsPHO2 in attenuating Phe toxicity in the seed. In +Phe WT, the relative expression level of OsPHO2 in the shoots was significantly lower, while those of Pi transporters (PTs) OsPT4 and OsPT8 were significantly higher in the roots compared with -Phe. Together, the results provided evidence towards the involvement of Pi in OsPHO2-regulated translocation and accumulation of Phe in rice.