Assessment of CuO NPs on soil microbial community structure based on phospholipid fatty acid techniques and phytotoxicity of bok choy seedlings.

In this study, a soil culture and a hydroponic experiment were conducted to assess the toxicology effects of copper oxide nanoparticles (CuO NPs) on soil microbial community structure and the growth of bok choy. Results showed CuO NPs had an inhibitory effect on soil microbial abundance, diversity, and activity, as well as the bok choy seedling growth, whereas CuO NPs at low concentrations did not significantly affect the soil microbial biomass or plant growth. In soil, CuO NPs at high dose (80 mg kg-1) significantly reduced the indexes of Simpson diversity, Shannon-Wiener diversity and Pielou evenness by 3.7%, 4.9% and 4.5%, respectively. In addition, CuO NPs at 20 and 80 mg kg-1 treatment significantly reduced soil enzymes (urease, alkaline phosphatase, dehydrogenase, and catalase) activities by 25.5%-58.9%. Further, CuO NPs at 20 mg L-1 significantly inhibited the growth of plant root by 33.8%, and catalase (CAT) activity by 17.9% in bok choy seedlings. The present study can provide a basis for a comprehensive evaluation of the toxicity effect of CuO NPs on soil microorganisms and phytotoxicity to bok choy seedlings.

Selenate regulates the activity of cell wall enzymes to influence cell wall component concentration and thereby affects the uptake and translocation of Cd in the roots of Brassica rapa L.

Selenium (Se) can be used to counteract cadmium (Cd) toxicity in plants. However, mechanisms underlying the alleviation of Cd toxicity by Se have not been completely elucidated, especially those by which Se reduces Cd translocation. A hydroponic experiment was performed to illustrate the regulatory mechanisms of Cd transport by selenate (Se (VI)) in pakchoi (Brassica rapa L., LvYou 102). The results showed that this plant had a high accumulation capacity for Cd, and Se(VI) addition restricted Cd translocation from roots to shoots. Se(VI) exposure stimulated the concentrations of pectins and hemicellulose II but reduced the concentration of hemicellulose I in the roots. In many cases, the enzymes pectin methylesterase, polygalacturonase, and ß-galactosidase were dose-dependently triggered by Se(VI) under Cd exposure, but root calcium concentration was significantly lowered (p < 0.05). Xyloglucan endoglycosidase (hydrolase) was triggered by Se(VI) under 2 mg L-1 Cd exposure and cellulase was generally activated by Se(VI) under Cd stress. The above results suggest that Se(VI) up-regulates pectin methylesterase activity, stimulates synthesis of pectins, and down-regulates root Ca concentration to release free carboxyl groups to combine Cd. In this study, the relationships between enzyme activity (e.g., peroxidase, superoxidase and ß-galactosidase), hydrogen peroxide, cell wall structure strengthening/loosening, and Cd toxicity affected by Se(VI) were also discussed.

Underlying mechanisms responsible for restriction of uptake and translocation of heavy metals (metalloids) by selenium via root application in plants.

Since selenium (Se) was shown to be an essential element for humans in 1957, the biofortification of Se to crops via foliar spraying or soil fertilization has been performed for several decades to satisfy the daily nutritional need of humans. Appropriate doses of Se were found to counteract a number of abiotic and biotic stresses, such as exposure to heavy metals (metalloids) (HMs), via influencing the regulation of antioxidant systems, by stimulation of photosynthesis, by repair of damaged cell structures and functions, by regulating the metabolism of some substances and the rebalancing of essential elements in plant tissues. However, few concerns were paid on why and how Se could reduce the uptake of a variety of HMs. This review will mainly address the migration and transformation of HMs regulated by Se in the soil-plant system in order to present a hypothesis of why and how Se can reduce the uptake of HMs in plants. The following aspects will be examined in greater detail, including 1) how the soil characteristics influences the ability of Se to reduce the bioavailability of HMs in soils and their subsequent uptake by plants, which include soil Se speciation, pH, water regime, competing ions and microbes; 2) how the plant root system influenced by Se affects the uptake or the sequestration of HMs, such as root morphology, root iron plaques and root cell wall; 3) how Se combines with HMs and then sequesters them in plant cells; 4) how Se competes with arsenic (As) and thereby reduces As uptake in plants; 5) how Se regulates the expression of genes encoding functions involved in uptake, translocation and sequestration of HMs by Se in plants.