Li P

Isolation and Molecular Detection of Polycyclic Aromatic Hydrocarbon-Degrading Mycobacterium spp. from the Shenfu Wastewater Irrigation Area in China

Mycobacterium spp. with the ability to degrade polycyclic aromatic hydrocarbons (PAHs) have attracted great attention. This study aims to isolate pyrene-degrading Mycobacterium spp. through direct plating and selective enrichment from sediment and paddy soil from several sites in Shenfu Wastewater Irrigation Area, and the diversity, catabolic genes and substrate utilization patterns of these pyrene-degrading Mycobacterium isolates was investigated. The Mycobacterium community dynamics was monitored during enrichment cultures by Denaturing Gradient Gel Electrophoresis (DGGE) to determine whether the Mycobacterium sp. detected in DGGE gels was successfully recovered. The results showed that a total of 20 unique Mycobacterium isolates were collected including 3 strains from direct plating and 17 from enrichment cultures. In addition to pyrene, most of the isolates could also degrade phenanthrene and fluoranthene and contained nidA and nidA3 genes, and only half of isolated strains were found to possess the pdoA2 gene. DGGE results showed that the Mycobacterium community had a shift in diversity during enrichment process. phylogenetic analysis based on 16SrDNA sequences from bands excised from DGGE gels and from these isolates revealed that isolated Mycobacterium spp. were represented of bands excised from DGGE gels in a small proportion. This collection of isolates will be valuable in bioremediation of PAH-contaminated sites.

The Possible Mechanisms of Cadmium Accumulation in Tagetes erecta L. under Macronutrient Deficiency

An experiment was conducted under hydroponic culture conditions to determine effects of nutrient deficiencies on cadmium (Cd) accumulation of Tagetes erecta L. and its possible mechanisms. Seedlings of similar size were pre-cultured in either N- or P- deprived nutrient solution for 7 days before exposure to 0.1 mg Cd L-1. The control plants had normal nutrient supply before and during Cd exposure. The plants were harveste after 7 days exposure to Cd. In N-deprived plants, Cd levels in roots, stems and roots were significantly reduced, which was consistent with a decrease of phytochelatins (PCs) in roots. Cd accumulation was the lowest in N-deficient plants, corresponding to substantial decreases in organic acids. In P-deprived plants, the obvious increase of Cd content in the root and stem and decrease of Cd content in the leaf accorded with increases of citric acid in the root and malic acid in the stem, supporting the suggestion that organic acids sequester soluble Cd and reduce Cd transport into the leaf.

Arbusular Mycorrhizal Fungi Effects of the Growth, Cd Uptake and Physiology of Solanum lycopersicum Seedlings under Cd Stress

The effects of three arbuscular mycorrhizal fungi (AMF) on the growth, Cd uptake and some physio-biochemical indexes of Solanum lycopersicum seedlings under different levels of Cd stress were investigated in a pot study. Generally, the symbiotic relationship between Solanum lycopersicum and AMF can be well established under Cd stress. This was reflected by the better physio-biochemical index of the plants inoculated with G. constrictum, G. mosseae and G. intraradices whose colonization rates were between 41.4% and 76.1%. Compared with the non-inoculated ones, G. constrictum inoculation enhanced the plant biomass at 50 mg kg-1 Cd addition level. AM colonization increased the Cd distribution to the roots in plants and alleviated shoots from high Cd stress, and thus increased the shoot biomass in the end. At the high Cd addition level, mycorrhizal plants reacted differently in the reduction of the contents of MDA, by influencing the soluble sugar, POD activity, SOD activity and so on. Our results showed that mycorrhizal colonization was beneficial to the Cd translocation in plants and reduced the membrane lipid peroxidation in plants under serious Cd stress. However, the mechanisms of mycorrhizal protection in plants were influenced by many factors and still need to be further studied.

Studies on the Mechanism of Cadmium Accumulation in Tagetes erecta L

Hydroponic experiments were carried out to study the effects of cell division inhibitor (Maleic hydrazide MH) and protein synthesis inhibitor（Cycloheximide CHI）on Cd accumulation in Tagetes erecta L and their possible mechanisms. Seedlings were exposed to 4 mmol L-1 MH or 3 µmol L-1 CHI in 0.1 mg L-1 Cd-containing solution for 3 days. After treatment, the Cd content in leaves was significantly (P<0.05) reduced under MH or CHI treatment, which was consistent with the decreased soluble protein contents in leaves, suggesting that protein synthesis plays a role in Cd accumulation in leaves of Tagetes erecta L. Both of the plant growth inhibitors led to increased Cd contents in roots compared with the control, corresponding with increased GSH, Cys or γEC content under MH or CHI treatment, indicating that those S-containing compounds may be related to the increased Cd content in roots under the plant growth inhibitor treatments. On the other hand, the two inhibitors increased the citric acid content in all the tissues of Tagetes erecta L except for that in leaves under CHI treatment. All the results suggest that protein synthesis may be responsible for Cd accumulation in leaves of Tagetes erecta L, while the S-containing compounds and organic acids are associated with Cd absorption in roots of Tagetes erecta L.