Responses in Plant Growth and Root Exudates of Pistia stratiotes under Zn and Cu Stress.

At present, the situation regarding heavy metal pollution in aquatic environments is becoming more and more serious. The bioaccumulation of heavy metals in aquatic plants causes obvious phytotoxicity, which can also induce secondary pollution in the aquatic environment. Zinc and copper, as indispensable elements for plant growth, are also prominent heavy metals in water pollution in China, and their concentrations play a crucial role in plant growth. In this study, we investigated the response of Pistia stratiotes (P. stratiotes) to different concentrations of Zn and Cu, and the results showed that plant growth and photosynthesis were inhibited under both Zn (1, 2, 4, and 8 mg/L) and Cu (0.2, 0.4, 0.8, and 1 mg/L) stresses. The relative growth rates of P. stratiotes under 8 mg/L Zn or 1 mg/L Cu stress were 6.33% and 6.90%, which were much lower than those in the control group (10.86%). Meanwhile, Zn and Cu stress caused insignificant change in the relative water contents of plants. The decrease in phlorophyll fluorescence parameters and chlorophyll contents suggested the significant photoinhibition of Zn and Cu stress. Chemical analysis of plant root exudates showed that the root secretion species obtained by gas chromatography-mass spectrometry (GC-MS) mainly included amino acids, alkanes, aldehydes, ketones, phenols, and more. Compared with the control group, the influence of Zn or Cu on the reduction in relative amounts of exudates was greater than that on the increase. The results of this study provide important data for the utilization of P. stratiotes in heavy metal-polluted water environments.

Insight into the absorption and migration of polystyrene nanoplastics in Eichhornia crassipes and related photosynthetic responses.

Nanoplastics, as emerging contaminants are being released into aquatic environments with their increasing applications, and induce potential hazards to aquatic ecosystem. In this work, we investigated the removal process of polystyrene nanoparticles (PS NPs) by Eichhornia crassipes and the related photosynthetic responses of E. crassipes. Results showed that both sizes of PS NPs (20 and 200 nm) with 50 mg/L induced the prominent damage on the root epidermis after 48 h exposure, and smaller size PS NPs caused the greater damage. PS NPs has been entered the roots of E. crassipes and migrated from the epidermis, cortex, to vascular system by using confocal laser scanning microscopy observation. Scanning electron microscope images confirmed the distribution of PS NPs (200 nm) in the roots. The crack at sites of primary-lateral root junction was an important way for the uptake of PS NPs, which destroyed the defense of Casparian strip, and promoted the migration of PS NPs into the vascular system. PS NPs entered the submerged leaves by stomata and the intercellular spaces of lower epidermis. Moreover, PS NPs in the plants showed significant inhibition on net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate. This study concluded the absorption and migration processes of PS NPs by E. crassipes, and the negative effects on photosynthesis, which will be useful for guiding the floating plants application for PS NPs removal in aqueous environment and ecological improvement.

Epidemiology of dental caries and its influences on jaw function in children / 中国学校卫生

Objective@#To understand and analyze the epidemiological characteristics of dental caries in children and its effects on jaw function, so as to prevent occurrence of abnormality of jaw function.@*Methods@#In October 2020, 860 cases of children from 5 kindergartens and 3 primary schools in Beijing were selected by adopting the convenience sampling method. All of them received oral examination, and the questionnaire according to the fourth national oral health epidemiological survey standard, including demographic information, eating habits, oral hygiene habits, oral health care,etc. The epidemiological characteristics of dental caries in children and its effects on jaw function were analyzed.@*Results@#A total of 190 children had dental caries, with a dental caries incidence rate of 22.09%. Dental caries in children s deciduous teeth or permanent teeth was related to age, residence, parents education level,whethe to eat before going to bed, whether eating sweet food, tooth brushing age, daily brushing frequency, whether parents have assisted tooth brushing, whether regular oral examination, whether parents have received oral health guidance( χ 2= 5.04 ,4.70，75.37，7.91，12.03，9.30，7.64，255.47，253.27，11.38, P <0.05). Compared with the noncaries group[(81.52±3.16， 80.54± 1.52，1.92±0.25，31.52±1.62，33.63±3.41，50.72±1.68)°], the sella nasion A point(SNA), sella nasion B point(SNB),A point nasion B point(ANB),frankfot horizontal mandibular plane angle(FH MP),skull nasion mandibular plane angle(SN MP),anteriors relationship palataplane mandibular(Ptm ANS) decreased in the dental caries group[(78.62±2.11，79.35±1.02，1.68±0.32，30.69±0.45，32.15±3.02，48.62±1.21)°](t=78.62,79.35,10.94, 30.69, 32.15, 48.62, P<0.05).@*Conclusion@#The prevalence of caries in children was high and jaw structure abnormalities and dysfunction. It is suggested that caries prevention and control work should be carried out early to strengthen the prevention and control of oral disease education work.

Fracture resistance of endodontically treated teeth with cervical defects using different restorative treatments.

Background/purpose: The restoration of endodontically treated teeth (ETT) with cervical defects has been a challenge for dentists. The purpose of this study was to evaluate the effect of restorative treatment on the fracture resistance of ETT with cervical defects. Materials and methods: One hundred and twenty freshly extracted human intact straight-single-root maxillary premolars were randomly divided into 6 groups. Group 1 remained untreated. Cervical defects of 4 mm-depth and 3 mm-height were created in groups 2-6. Group 3-6: root canal treatment. Group 4: direct composite resin restoration. Group 5: 2-mm full-cusp-coverage composite resin restoration. Group 6: fiber-post-supported composite resin restoration. A static fracture test was used to determine the fracture resistance of teeth under axial (n = 10) and palatal (30°) (n = 10) loading. Fracture modes were categorized as restorable and unrestorable. Results: Compared with intact teeth, the axial fracture resistance of teeth with cervical defects decreased by approximately 39%, and endodontic procedures resulted in 10% more reduction. When ETT with cervical defects were restored using direct composite resin filling, the axial fracture resistance recovered to 72% of that of intact teeth, but no significant change occurred under oblique loading. After full-cusp-coverage or fiber-post-supported restoration, fracture resistance showed complete recovery to the value of intact teeth (P > 0.05). Sixty percent of fractures were unrestorable for fiber-post-supported teeth, while in the full-cusp-coverage restoration group, 80-90% of fractures were restorable. Conclusion: Full-cusp-coverage restoration or fiber-post-supported restoration could improve the fracture resistance of ETT with cervical defects, whereas unrestorable fractures easily occurred in fiber-post-supported restorations.