Response of Vicia faba to short-term uranium exposure: chelating and antioxidant system changes in roots.

Uranium (U) phytotoxicity is an inherently difficult problem in the phytoremediation of U-contaminated environments. Plant chelating and antioxidant systems play an authoritative role in resistance to abiotic stress. To reveal the toxicity of U, the changes of chelating system, osmoregulatory substances and antioxidant systems in Vicia faba roots were studied after short-term (24 h) U exposure. The results indicated that the development of lateral roots and root activity of V. faba were significantly inhibited with U accumulation. Compared with the control, plant chelating systems showed significant positive effects after U exposure (15 - 25 µM). Osmoregulatory substances (proline and soluble protein) increasingly accumulated in roots with increasing U concentration, and O2- and H2O2 rapidly accumulated after U exposure (15 - 25 µM). Thus, the contents of malondialdehyde (MDA), a marker of lipid peroxidation, were also significantly increased. Antioxidant systems were activated after U exposure but were inhibited at higher U concentrations (15 - 25 µM). In summary, although the chelating, osmotic regulation and antioxidant systems in V. faba were activated after short-term U exposure, the antioxidases (CAT, SOD and POD) were inhibited at higher U concentrations (15 - 25 µM). Therefore, the root cells were severely damaged by peroxidation, which eventually resulted in inhibited activity and arrested root development.

Effects of strontium on the morphological and photosynthetic physiological characteristics of Vicia faba seedlings.

The adaptation of plants to strontium (Sr) stress requires a more systematic understanding. In the present study, the morphological and photosynthetic physiological characteristics of Vicia faba seedlings under Sr stress (88Sr, 0-1,000 mg·L-1) were analyzed in solution culture. The results showed that Sr treatment decreased the biomass and root activity of V. faba seedlings significantly, but fortunately, there was almost no root necrosis. In plant morphology, the taproot length, lateral root number, plant height, branching number and internodes number of V. faba were significantly inhibited, thus the apical dominance of taproot and terminal bud was more obvious. The accumulation of Sr resulted in the decrease of leaf area, dry weight, stomatal density and stomatal aperture, while the guard cell length increased, and the specific leaf weight (SLW) increased first and then decreased. These changes in stomatal morphology may be a positive regulation to reduce water loss. In addition, V. faba increased the non-photochemical quenching (NPQ) and the activities of peroxidase (POD) and ascorbate peroxidase (APX) to protect the photosynthetic structure. Low concentration of Sr (250 mg·L-1) promoted the photochemical efficiency and electron transfer of PSII (e.g., increased Fv/Fm, ΦPSII, qP and ETR). However, Sr (250-1,000 mg·L-1) inhibited the net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) in leaves. In general, the Pn was affected by both stomatal and non-stomatal factors. Since Sr did not cause significant damage to the PSII function, the non-stomatal factor may be the dark reaction in photosynthesis affected, but this needs to be proved by further studies.

Recently, strontium (Sr) pollution has become a global environmental problem. There is still a lack of systematic understanding of plant morphological and physiological responses to Sr stress. Therefore, V. faba, a Sr-accumulation plant, was used as the experimental material to systematically understand the adaptation characteristics of plants to Sr stress, which provide reference for the application of plants in the remediation of Sr pollution.

Effects of U on the growth, reactive oxygen metabolism and osmotic regulation in radish (Raphanus sativus L.).

Uranium (U) is a non-essential and toxic element, so it is necessary to study the physiological mechanism of plant response to U stress. The present study evaluated the growth status, reactive oxygen metabolism and osmotic regulation system in radish (Raphanus sativus) under U stress (0, 25, 50 and 100 µM). The results showed that U had no significant effect on the germination of radish seeds but inhibited the growth of seedlings, such as reduced root activity and increased plasma membrane permeability. U is mainly distributed in radish roots, so it poisons the roots more than the aboveground parts. When U concentration was 25 µM, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities in radish were increased to cope with the oxidative stress caused by U stress, and the accumulation of proline and soluble sugar was increased to maintain cell turgor. However, under high concentration (100 µM), the damage of radish root was serious; thus, the SOD, CAT and soluble sugar could not respond to U stress. In conclusion, the identification and characterization of U-stress responses in genuine U-tolerant plants would improve our knowledge on the detoxification of this radionuclide.

[Research progress in the osteogenetic mechanism of strontium].

Strontium (Sr) is an essential trace element and widely exists in nature. It plays an important role in the in vivo regulation of bone metabolism. Sr locates below Fe in the periodic table, and its chemical structure and polarity are similar to those of Ca. It can induce bone mesenchymal stem cells to differentiate into osteoblasts by inhibiting the activity of osteoclasts and reducing bone resorption. It promotes bone formation through a series of related pathways. The mechanism of Sr regulation of bone metabolism has been extensively researched in recent years. The current study aims to investigate the mechanism of Sr and provide a theoretical basis for its clinical application.

Fabrication and characterization of strontium-hydroxyapatite/silk fibroin biocomposite nanospheres for bone-tissue engineering applications.

Osteoinductive bone filling biomaterials are in high demand for effective bone defect reconstruction. In this study, we aimed to design both organic and inorganic substances containing strontium-doped hydroxyapatite/silk fibroin (SrHA/SF) biocomposite nanospheres as an osteoinductive bone defect-filling biomaterial. SrHA/SF nanospheres were prepared with different concentration of Sr using ultrasonic coprecipitation method. The nanospheres were characterized using XRD, FTIR, SEM, TEM, ICP-AES and TGA. Solid and dense SrHA/SF nanospheres with 500-700 nm size and rough surfaces were synthesized successfully. Higher crystallinity and HA/SF phase were observed with the increase in Sr-concentration. The doping of different concentration of Sr did not affect the size and surface characteristics of the nanospheres. ICP-AES data showed that Sr/Ca ratio in SrHA/SF is very close to the nominal value. Nanospheres with higher concentration of Sr did not negatively affect the biocompatibility, but enhanced viability of mesenchymal stem cells (MSCs). Moreover, SrHA/SF nanospheres showed higher osteogenic differentiation potential compared to HA/SF nanospheres as indicated by the results from ALP staining, ALP activity, and Runx2, Alp, Col-1 and Opn gene expression assay in MSCs culture. Our findings suggest this novel design of biocompatible and osteoinductive SrHA/SF biocomposite nanospheres as a potential bone defect-filling biomaterial for bone regenerative applications.

A comparative study of the effects of concentrated growth factors in two different forms on osteogenesis in vitro.

Extending the release cycle of growth factors to match the cycle of bone remodeling is difficult. When using concentrated growth factors (CGFs), the release of growth factors is excessively rapid. In the present study, CGF samples were prepared by centrifugation. CGF samples were then lyophilized and grinded into a powder, which was termed freeze­dried CGF. The freeze­dried CGF samples were mixed with chitosan­alginate composite hydrogels, and the mixture was lyophilized. The result was a chitosan­alginate composite CGF membrane, which was called sustained­release CGF. This study investigated whether freeze­dried CGF in a chitosan­alginate composite gel can release CGF steadily to achieve effective osteogenesis. The proliferation and osteogenic expression of MC3T3­E1 cells induced by the supernatants from incubation with freeze­dried CGF and sustained­release CGF were evaluated. The concentrations of the growth factors, transforming growth factor ß1 (TGF­ß1), insulin­like growth factor­1 (IGF­1), platelet­derived growth factor­AB (PDGF­AB) and vascular endothelial growth factor (VEGF), in these two experimental groups at different times were determined by ELISA kits. The freeze­dried CGF showed better osteogenic performance than the sustained­release CGF in the early stages. At later stages, the sustained­release CGF had significant advantages over freeze­dried CGF in terms of promoting osteogenic mineralization. By characterizing the biologic properties of the CGF in the two different forms in vitro, we obtained a better understanding of their clinical effects.