Convenient Heme Nanorod Modified Electrode for Quercetin Sensing by Two Common Electrochemical Methods.

Quercetin (Qu) is one of the most abundant flavonoids in the human diet. High concentrations of Qu can easily cause adverse effects and induce inflammation, joint pain and stiffness. In this study, Heme was used as a sensitive element and deposited and formed nanorods on a glassy carbon electrode (GCE) for the detection of Qu. The Heme/GCE sensor was characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques. Under optimized conditions, the developed sensor presented a linear concentration ranging from 0.1 to 700 µmol·L-1 according to the CV and DPV methods. The detection limit for the sensor was 0.134 µmol·L-1 and its sensitivity was 0.12 µA·µM-1·cm-2, which were obtained from CV analysis. Through DPV analysis we obtained a detection limit of 0.063 µmol·L-1 and a sensitivity of 0.09 µA·µM-1·cm-2. Finally, this sensor was used to detect the Qu concentration in loquat leaf powder extract, with recovery between 98.55-102.89% and total R.S.D. lower than 3.70%. The constructed electrochemical sensor showed good anti-interference, repeatability and stability, indicating that it is also usable for the rapid detection of Qu in actual samples.

[Mechanism of heavy-metal tolerance in Pseudomonas aeruginosa ZGKD2].

The cadmium-resistant bacterium Pseudomonas aeruginosa strain ZGKD2 exhibiting tolerance to various heavy-metals was isolated from gangue pile of coal area in our laboratory. This bacterium could serve as an effective metal sequestering and growth-promoting bioinoculant for plants grown in metal-contaminated soil. However, the mechanism of heavy-metal tolerance is still unclear. When the beef extract-peptone medium was supplemented with 200-3 000 micromol x L(-1) Cd2+, Cu2+, Zn2+, Ni2+, Pb2+ or Mn2+, the maximum biomass of strain ZGKD2 decreased with the increase of heavy-metal concentrations, while different concentrations of heavy-metals had no significant effect on its alkaline production. Stationary-phase cells of strain ZGKD2 were exposed to 0, 200, 600 and 1 000 micromol x L(-1) of Cd2+ , Cu2+, Zn2+ and Ni2+ or 0, 1 000, 2 000 and 3 000 micromol x L(-1) of Pb2+ and Mn2+ for 2 h, respectively. The activity of SOD and CAT increased in a heavy-metal-concentration-dependent manner, especially in the Cd2+ and Cu2+ treatments. The siderophore production of strain ZGKD2 in modified sugar-aspartic acid medium was enhanced by 200- 1 000 micromol x L(-1) of various heavy-metals. Cd2+ and Zn2+ strongly induced the siderophore production of strain ZGKD2, Ni2+ and Mn2+ had little effect, whereas Cu2+ led to significant inhibition. The siderophore production of strain ZGKD2 was positively related with its metal tolerance. These results indicated that alkaline production, siderophore production, and the increase of antioxidant enzyme activities in strain ZGKD2 might be the main mechanisms of heavy-metal tolerance.

[Antioxidative enzymes play key roles in cadmium tolerance of Phytolacca americana].

Phytolacca americana L. has the capacity to take up and accumulate to very high levels heavy metals such as Mn and Cd, and is used for phytoextraction of heavy metal contaminated soils. The role of antioxidative enzyme of Phytolacca americana in response to Cd stress is unknown. The 6-week-old seedlings of Phytolacca americana were exposed to half strength Hoagland solution with 200 micromol/L CdCl2 or 400 micromol/L CdCl2 for 4 days. The content of H2O2 and MDA, and electrolyte leakage increased, while the photosynthetic rate decreased, indicated that the oxidative damage induced by Cd stress in Phytolacca americana was one of the metal toxicity mechanism. The activities of SOD and POD increased rapidly with elevated Cd concentration and exposure time, CAT activity was stable in response to 200 micromol/L CdCl2 stress, and increased only at 3 d later upon 400 micromol/L CdCl2, treatment. Suggested that the enzymatic antioxidation capacity played important role in Cd tolerance of hyperaccumulator plant.