Response and tolerance of root border cells to aluminum toxicity in soybean seedlings.

Root border cells (RBCs) and their secreted mucilage are suggested to participate in the resistance against toxic metal cations, including aluminum (Al), in the rhizosphere. However, the mechanisms by which the individual cell populations respond to Al and their role in Al resistance still remain unclear. In this research, the response and tolerance of RBCs to Al toxicity were investigated in the root tips of two soybean cultivars [Zhechun No. 2 (Al-tolerant cultivar) and Huachun No. 18 (Al-sensitive cultivar)]. Al inhibited root elongation and increased pectin methylesterase (PME) activity in the root tip. Removal of RBCs from the root tips resulted in a more severe inhibition of root elongation, especially in Huachun No. 18. Increasing Al levels and treatment time decreased the relative percent viability of RBCs in situ and in vitro in both soybean cultivars. Al application significantly increased mucilage layer thickness around the detached RBCs of both cultivars. Additionally, a significantly higher relative percent cell viability of attached and detached RBCs and thicker mucilage layers were observed in Zhechun No. 2. The higher viability of attached and detached RBCs, as well as the thickening of the mucilage layer in separated RBCs, suggest that RBCs play an important role in protecting root apices from Al toxicity.

[Analysis of roots of soybean (Glycine max Merrill) treated with exogenous citric acid plus short-time aluminum stress by direct determination of FTIR spectrum].

In the present study, 19 soybean (Glycine max L.) cultivars were analyzed and found to differ considerably in aluminum (Al) resistance. The cultivars Zhechun No. 2 (Al-resistant) and Zhechun No. 3 (Al-sensitive) were selected for further analysis. Experiments were performed with plants grown in full nutrient solution for 30 days. Fourier transform infrared spectrometry (FTIR) with OMNI-sampler was applied to the direct determination of different varieties of soybean root tissues, treated with aluminum in a dose-and time-dependent manner plus exogenous citric acid. Then the characteristic absorption peaks of spectra were analyzed and some differences in the FTIR spectra among samples were found from the comparison of the spectra. Results showed that the intensity and the shape of absorption peaks of their FTIR spectra exhibited some differences between different kinds of soybean and different treatment, especially around 1 057, 1 602, 2 927 and 3 292 cm(-1), which mainly reflected the content variety of protein, glucide, nucleic acid and so on. Thus it could be concluded that the effect of aluminum stress and existence of exogenous citric acid did not change the component of chemical substance in soybean roots, although the content of certain substance varied. The two dimensional discriminates analysis chart was drawn by the ratio of area at 2 927 cm(-1) to that at 3297 cm(-1) as the abscissa vs the ratio of area at 1 057 cm(-1) to that at 1 602 cm(-1) as the vertical, to discover the difference between the treatment of aluminum plus exogenous citric acid and that of single aluminum. Result indicates that the difference in the shape of absorption peaks of FTIR spectra became smaller and that presumed the content variety with different treatment was not remarkable under the condition of exogenous citric acid, especially in Zhechun No 3. From all mentioned above it is made clear that exogenous citric acid could really ameliorate distinctly the effect of aluminum on soybean roots which was detected by direct determination of FTIR spectrum, giving the fact that FTIR could reflect the ameliorating effect of exogenous organic acid on plant tissue under aluminum stress.

[FTIR spectroscopic characterization of chromium-induced changes in root cell wall of plants].

Due to its wide industrial use, chromium is considered a serious environmental pollutant. Contamination of soil and water by chromium (Cr) is of recent concern. Chromium mainly accumulates in root in plants, and the change in compounds of the root cell wall have a close relation with the Cr accumulation. Compared with the other identification methods, the identification of the Chinese traditional and herbal drugs using Fourier transform infrared spectrometer with OMNI collector is simple and convenient, fast and accurate. In the present paper, the spectra of cell wall of Cr-treated root and control of Eichhornia crassipes and Alternanthera philoxeroides were determined. Absorption peaks were identified to the corresponding functional groups and half-quantitative analysis was also used. The results showed that a significant shift of -OH absorption peaks can be seen when comparing the FTIR spectra of control and Cr-treated plants, and the absorbency of -OH and COO- groups went up in E. crassipes root cell wall while droped in A. philoxeroides root cell wall. It is suggested that -OH and COO groups were referred in binding Cr6+ in aqueous solutions, and this may be included in the mechanism of Cr accumulation in E. crassipes roots. Therefore, FTIR spectrometry could be widely used to monitor changes in chemical composition of plant parts under stresses and environmental restoration.

Developmental characteristics and response to iron toxicity of root border cells in rice seedlings.

To investigate the Fe2+ effects on root tips in rice plant, experiments were carried out using border cells in vitro. The border cells were pre-planted in aeroponic culture and detached from root tips. Most border cells have a long elliptical shape. The number and the viability of border cells in situ reached the maxima of 1600 and 97.5%, respectively, at 20-25 mm root length. This mortality was more pronounced at the first 1-12 h exposure to 250 mg/L Fe2+ than at the last 12-36 h. After 36 h, the cell viability exposed to 250 mg/L Fe2+ decreased to nought, whereas it was 46.5% at 0 mg/L Fe2+. Increased Fe2+ dosage stimulated the death of detached border cells from rice cultivars. After 4 h Fe2+ treatment, the cell viabilities were > or =80% at 0 and 50 mg/L Fe2+ treatment and were <62% at 150, 250 and 350 mg/L Fe2+ treatment; The viability of border cells decreased by 10% when the Fe2+ concentration increased by 100 mg/L. After 24 h Fe2+ treatment, the viabilities of border cells at all the Fe2+ levels were <65%; The viability of border cells decreased by 20% when the Fe2+ concentration increased by 100 mg/L. The decreased viabilities of border cells indicated that Fe2+ dosage and treatment time would cause deadly effect on the border cells. The increased cell death could protect the root tips from toxic harm. Therefore, it may protect root from the damage caused by harmful iron toxicity.

[Identification of aluminum toxicity of soybean in red soil region with FTIR, TG and DT technology].

Aluminum (Al) toxicity is one of the major constraints to crop production in acid soils. In order to provide a correct and effective identification method of aluminum toxicity of soybean in red soil regions, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential thermal (DT) analysis were adopted to study the soybean root under different Al treatments. The results showed that the aluminum contents of soybean roots treated with 60 and 90 mg x L(-1) Al concentration were higher than that with other aluminum treatment, and the Al content reached significant aluminum toxicity level. In the same wavenumber range, the character, wavenumber and absorption peak of infrared spectra were different from those under different Al treatments. In summary, the absorption peaks at 3300, 2 930, 1542 and 721 cm(-1) were the characteristic peaks for identification that can be used to evaluate the Al toxicity of soybean. Detailed description is as follows: with the high aluminum treatment (60 and 90 mg x L(-1)), the characteristic peaks at 3300 and 2930 cm(-1) were higher than those with other aluminum treatment. There are no infrared bands at 1542 cm(-1) under 90 mg x L(-1) aluminum treatment, as the characteristic peak of Amide II. However, the characteristic peak at 721 cm(-1) was clearly shown at 60 and 90 mg x L(-1), but no sign was shown in 0, 10 and 30 mg x L(-1) aluminum concentration. Curves of TG and DT revealed the greatest difference with different Al treatment in the range of temperature of 400-500 degrees C. Under the Al treatment above 30 mg x L(-1), TG curve had less weight than that at 0 mg x L(-1), which indicated that the root system may be more lignified, producing some material hard to be burned. DT curve had double peaks at 60 and 90 mg x L(-1) Al treatments, which may also be used as identification mark of Al toxicity. Because some features were expressed under Al treatment with FTIR, TG and DT, the technology of FTIR, TG and DT provided a new way to identify Al toxicity of soybean in red soil region.