Zhenggui Wei

Effect of earthworms on the phytoremediation of zinc-polluted soil by ryegrass and Indian mustard

In this paper, the effects of earthworms on the growth and Zn uptake of ryegrass and Indian mustard in artificially Zn-contaminated soils were studied. Earthworm inoculation increased plant shoot biomass by 29–83% for ryegrass and by 11–42% for Indian mustard, respectively, as compared to the treatments without earthworms, while the roots’ biomass of both plants were increased much more than their corresponding shoots. Earthworms also increased shoot Zn concentrations in both ryegrass and Indian mustard, although the increases in ryegrass did not show significant difference. Except for soil without Zn contamination, the Zn contents of both ryegrass and Indian mustard roots were significantly increased by earthworm addition. Generally, Zn contents of roots were relatively higher than those of shoots for both plants, which were independent of earthworms inoculation. Earthworm increased soil bioavailable metal (diethylenetriamine-pentaacetic acid–Zn) (DTPA-Zn) concentrations, which resulted in a direct increase in Zn uptake by the plants, since a significant correlation was observed between the DTPA–Zn contents and plant Zn uptake. However, the main reason for the increase in plant Zn uptake under earthworm inoculation was probably the increase in dry matter production stimulated by earthworms.

Elimination of the Interference from Nitrate Ions on Oxalic Acid in RP-HPLC by Solid-Phase Extraction with Nanosized Hydroxyapatite

Abstract A new method using solid phase extraction with nanosized hydroxyapatite for solving interference from nitrate ions on oxalic acid in reversed phase high performance liquid chromatography (RP-HPLC) was developed. The optimum experimental conditions for the separation and determination of oxalic acid were studied. After the interference was eliminated, oxalic acid was determined by RP-HPLC at the optimum chromatographic conditions with an average recovery ranging between 94.8% and 99.3%, and the relative standard deviations were less than 3.0%. This method was successfully applied to determine the oxalic acid in the xylem saps of tomato.

Roles of Organic Acids and Nitrate in the Long-Distance Transport of Cobalt in Xylem Saps of Alyssum murale and Trifolium subterraneum

Roles of organic acids and nitrate in the long-distance transport of cobalt (Co) in xylem saps of hyperaccumulator Alyssum murale and non-hyperaccumulator Trifolium subterraneum were studied under hydroponic conditions. Organic acids (oxalic, malic, malonic, citric, and fumaric) and nitrate in xylem sap samples were separated and determined simultaneously by reversed-phase high performance liquid chromatography after solid-phase extraction with nanosized hydroxyapatite. Results indicated that Co treatment significantly increased the concentrations of xylem oxalic and malic acids for the hyperaccumulator A. murale compared to the control but significantly decreased the concentrations of xylem nitrate and malonic acid; concentrations of citric acid in xylem sap samples did not show significant difference between the control and Co treatments. By analyzing the relationship between the concentrations of organic acids, nitrate, and concentrations of Co in xylem saps, it could be concluded that oxalic and malic acids in xylem saps seemed to participate in the long-distance Co translocation process, and citric acid did not relate to the xylem Co transport of A. murale and T. subterraneum. Our work might be very useful for understanding the mechanism of long-distance transport of heavy metals in hyperaccumulator.

Effects of low-molecular-weight organic acids on gadolinium accumulation and transportation in tomato plants

Effects of low-molecular-weight organic acids on the accumulation and transportation of gadolinium (Gd) in tomato plants were studied under hydroponic condition. The results indicated that changes of organic acids occurred in the processes of Gd accumulation and transportation in tomato plants which were treated with extraneous Gd solutions. Malic, citric, and succinic acids contributed to both Gd accumulation in roots and transportation in xylem vessels. When Gd was unloaded from the xylem to the leaf cells, formic, lactic, citric, and succinic acids played important roles in Gd accumulation in leaves. When tomato plants were cultured in the uptake solution of Gd-containing malic, citric, or succinic acid for 48 h, the succinic acid in roots and leaves and the malic acid in xylem saps both increased obviously. From the results above, we can conclude that succinic acid had the most important role in Gd accumulation in tomato roots and leaves, while malic acid transported Gd via xylem vessels more effectively.

Structural differences between light and heavy rare earth element binding chlorophylls in naturally grown fern: Dicranopteris linearis.

Chloroplasts and chlorophylls were isolated from the leaves of Dicranopteris linearis, a natural perennial fern sampled at rare earth element (REE) mining areas in the South-Jiangxi region (southern China). The inductively coupled plasma-mass spectrometry (ICP-MS) results indicated that REEs were present in the chloroplasts and chlorophylls of D. linearis. The in vivo coordination environment of light REE (lanthanum) or heavy REE (yttrium) ions in D. linearis chlorophyll-a was determind by the extended X-ray absorption fine structure (EXAFS). Results revealed that there were eight nitrogen atoms in the first coordination shell of the lanthanum atom, whereas there were four nitrogen atoms in the first coordination shell of yttrium. It was postulated that the lanthanum-chlorophyll-a complex might have a double-layer sandwichlike structure, but yttrium-binding chlorophyll-a might be in a single-layer form. Because the content of REE-binding chlorophylls in D. linearis chlorophylls was very low, it is impossible to obtain structural characteristics of REE-binding chlorophylls by direct analysis of the Fourier transform infrared (FTIR) and ultraviolet (UV)-visible spectra of D. linearis chlorophylls. In order to acquire more structural information of REE-binding chlorophyll-a in D. linearis, lanthanum—and yttrium-chlorophyll-a complexes were in vitro synthesized in acetone solution. Element analyses and EXAFS results indicated that REE ions (lanthanum or yttrium) of REE-chlorophyll-a possessed the same coordination environment whether in vivo or in vitro. The FTIR spectra of the REE-chlorophyll-a complexes indicated that REEs were bound to the porphyrin rings of chlorophylls. UV-visible results showed that the intensity ratios of Soret to the Q-band of REE-chlorophyll-a complexes were higher than those of standard chlorophyll-a and pheophytin-a indicating that REE-chlorophyll-a might have a much stronger ability to absorb the ultraviolet light. The MCD spectrum in the Soret band region of lanthanum-chlorophyll-a showed a special peak, but yttrium-chlorophyll-a did not have this special peak, corresponding well to their double-layer and single-layer structure, respectively. Structural differences between lanthanum—and yttrium-chlorophyll-a might result from the difference in ion radius between yttrium and lanthanum. These data might be useful for understanding of both the properties of REE-chlorophyll-a complexes and the physiological roles of REEs in the hyperaccumulator D. linearis.

The role of amino acids in the long-distance transport of La and Y in the xylem sap of tomato.

This study focuses on the role of amino acids in xylem sap of tomato grown in hydroponics in a medium supplemented with a series of concentration of La and Y. Eighteen amino acids in xylem saps were identified and measured by reversed-phase high-performance liquid chromatography. The main amino acids in xylem sap samples of the tomato are histidine, tryptophan, aspartic acid, and glutamic acid. The concentration of glutamic acid in xylem sap significantly increased in the La and Y treatment compared to the control. By analyzing the correlation between concentrations of amino acids and concentrations of La and Y in the xylem saps, we considered that the glutamic acid in xylem saps seemed to participate in the long-distance La and Y translocation processes, and histidine did not relate to xylem La and Y transport of tomato. The role of other amino acids which was excreted by tomato has not been demonstrated in the long-distance transport of La and Y in the xylem.

SIMULTANEOUS EXTRACTION AND DETERMINATION OF ORGANIC ACIDS IN XYLEM SAPS BY RP-HPLC AFTER SOLID-PHASE EXTRACTION WITH SMALLER PARTICLE-SIZED HYDROXYAPATITE NANOCRYSTALS

A simple and reliable RP-HPLC method based on solid-phase extraction with smaller particle sized hydroxyapatite nanocrystals was developed for the simultaneous extraction and determination of oxalic, malic, and citric acids in xylem saps of pokeweed. The smaller particle sized hydroxyapatite nanocrystals exhibited greater surface area and more active sites on the surface, consequently, higher adsorption ability to organic acids, which was proved to be an effective solid-phase extractor for the simultaneous extraction of organic acids in xylem saps. Oxalic, malic, and citric acids were determined by RP-HPLC at the optimum chromatographic conditions after the solid-phase extraction procedure. The accuracy of the method was confirmed with an average recovery ranging between 94.2% and 97.9%, the relative standard deviations (RSD) were less than 2.0%. This method was successfully applied to determine the organic acids in xylem saps of pokeweed.

Earthworm mucus enhanced cadmium accumulation of tomato seedlings.

A hydroponic experiment was carried out to study the effects of earthworm (Metaphire guillemi) mucus on tomato Hezuo 903 (Lycopersicon esculentum) seedlings growth and cadmium (Cd) accumulation. The experiment included three levels of Cd addition rates (0, 5 and 10 mg L−1), two levels of earthworm mucus addition (20 and 40 ml per pot) treatments (EML and EMH), and the control (CK). The results showed that compared with the control, earthworm mucus addition significantly increased shoot and root dry weights of tomato seedling by 13.8–44.5% and 12.4–33.2%, respectively. In contrast, high earthworm mucus addition (EMH) led to a 4% shoot weights decrease at 10 mg Cd L−1 compared with CK. Cadmium concentrations and accumulations in both shoot and root of tomato seedlings were significantly increased (p < 0.01) with increasing Cd and earthworm mucus addition levels. Cadmium concentrations and accumulations in root were much higher than those in corresponding shoot. Present study indicated that earthworm mucus could enhance tomato seedlings growth and Cd accumulation. Our work might be not only very useful for understanding how earthworms enhance plant growth and heavy metals accumulation, but also for further application of earthworms in phytoextraction.