树木硝酸还原酶的研究概况与应用前景

树木硝酸还原酶（NR）在林木生长中的作用越来越为人们所认识和重视。本文综述了树木NR研究的动态，讨论了NR在林业生产上的应用前景，分析了NR作为树木性状预测的生化指标的理论根据和应用领域，并根据当前树木NR研究的发展趋势，结合我国林业生产上的问题，提出了加快我国树木NR应用研究进展的建议。     

烤田对土壤中氮素和与氮有关的酶活性影响

在水稻分蘖期对5种不同尿素氮肥水平的小区进行烤田5天的试验。试验结果表明,在烤田过程中,脲酶活性变化不明显,呈微弱增加趋势。硝酸还原酶活性急剧降低,羟胺还原酶活性呈波动变化,几乎检测不到亚硝酸还原酶活性。土表的铵态氮也呈波动变化,随着烤田时间的增加铵态氮含量降低。土表的硝态氮浓度不断增加,烤田增大了复水后硝态氮向地下水淋溶的趋势。施氮量越多,土表的矿质氮含量也越多。土壤烤田的主要目的是通过降低土壤的含水量,提高土壤的氧化还原电位,改善土壤的通气状况。     

Selection and evaluation of nitrate-tolerant strains of Rhizobium leguminosarum biovar viceae specific to the lentil

Seventeen strains of Rhizobium leguminosarum biovar viceae specific to the lentil (Lens culinaris L.) were screened, using the high-yielding lentil cultivar L 4076, for their tolerance to three levels of NO _inf3 ^sup- : 0, 4, and 8 mM NO _inf3 ^sup- . Preliminary screening of this symbiosis for nodulation and N fixation in the presence of NO _inf3 ^sup- showed significant variations among the strains. The number of nodules decreased and nitrogenase activity was depressed in all strains in the presence of NO _inf3 ^sup- . Strains L-1-87, L-27-89, L-33-89, and L-40-89 tolerated 8 mM NO _inf3 ^sup- . Four strains, three tolerant of NO _inf3 ^sup- (L-1-87, L-27-89, and L-33-89), and one sensitive (L-11-89) to NO _inf3 ^sup- , were selected from preliminary screening and used in a pot experiment to assess the symbiosis in the presence of 6 mM NO _inf3 ^sup- at three stages of plant growth, viz., 40 days, 60 days, and at the final harvest. In general, the weight of nodules and C₂H₂ reduction activity was significantly higher after 60 days than after 40 days. Inoculation with strain L-1-87 produced the maximum number of nodules, and root and shoot biomass both in the presence and the absence of NO _inf3 ^sup- . Nitrate reductase activity in the tops and nodules was assayed only after 60 days and did not show significant variations among strains and NO _inf3 ^sup- treatments. The grain yields for all strains except L-11-89 were significantly higher in the presence of NO _inf3 ^sup- than in the absence of NO _inf3 ^sup- , indicating that tolerant strains contributed symbiotically fixed N to the plant's N pool, resulting in an additive effect on yield. Inoculation with strain L-1-87 produced the maximum grain yield and this strain appears to have potential use as an inoculant in the presence of high levels of soil N.     

缺铁胁迫对沙梨叶片黄化、再复绿和根系中Fe(Ⅲ)还原酶活性的影响

在水培条件下,研究了缺铁胁迫对梨砧木沙梨(Pyrus pyrifolia Nakai)叶片黄化、复绿和分根培养时其根系Fe(Ⅲ)还原酶活性(FCR)变化的影响。结果表明,黄化植株转移到含铁营养液后,上部叶片复绿明显快于中部叶片;含铁和不含铁处理间的FCR活性差异显著,不含铁处理的根FCR活性高于含铁处理,但随着培养时间的延长,活性逐渐降低,不含铁和含铁处理之间具显著的相关,相关系数为0.91。     

Molecular characterization of chromium (VI) reducing potential in Gram positive bacteria isolated from contaminated sites

Hexavalent chromium [Cr(VI)] is highly toxic, teratogenic and carcinogenic to man and other animals. Some bacterial species have the ability to reduce Cr(VI) to a stable speciation state of trivalent chromium [Cr(III)], which is insoluble and comparatively less toxic. Therefore, the reduction of Cr(VI) thus provides potential as a means for environmental bioremediation of Cr(VI) pollution. In the present study bacteria isolated from chromium and diesel contaminated sites were found to have the ability to rapidly reduce highly toxic concentrations of Cr(VI) to Cr(III) when grown in minimal medium supplemented with glucose as the sole carbon source. Partial chromate reductase gene sequences were retrieved after PCR amplification of genomic DNA extracted from three Gram positive isolates which were highly similar (>99% sequence similarity) to chromate reductase genes found in Gram negative bacteria, more specifically those identified from Escherichia coli and Shigella spp. whole-genome studies. The isolated bacteria were putatively identified by 16S rRNA gene sequencing as Arthrobacter aurescens strain MM10, Bacillus atrophaeus strain MM20, and Rhodococcus erythropolis strain MM30.     

植物亚硝基谷胱甘肽还原酶(GSNOR)功能的研究进展

亚硝基谷胱甘肽还原酶(GSNOR)能通过还原亚硝基谷胱甘肽(GSNO)途径调节细胞内一氧化氮(NO)和亚硝基硫醇(SNOs)水平,保护机体免受亚硝化胁迫的影响。在植物体内,GSNOR作为催化调节NO及其代谢物SNOs水平的关键酶,参与植物生长、抵御病原菌、热耐受性、细胞死亡和镉胁迫等多种生理过程。综述GSNOR功能的研究进展,分析存在的问题,有望为红掌、合果芋等热带观赏植物基因工程提供理论基础。     

Knockdown of RRM2 gene by siRNA inhibits human breast cancer cell proliferation,migration and tumor growth in nude mice

AIM: To explore the effect of ribonucleotide reductase M2 (RRM2) gene knockdown by siRNA on the proliferation and migration of human breast cancer MCF-7 cells and the tumor growth in BALB/c nude mice. METHODS: The mRNA and protein expression leves of RRM2 in human breast cancer cell line MCF-7 and human normal breast cell line MCF-10A were determined by real-time PCR and Western blotting. siRNA-RRM2 was constructed and transfected into MCF-7 cells at different time points and different concentrations. The silencing efficiency of RRM2 gene was detected by real-time PCR. The cell proliferation was measured by CCK-8 assay. The migration was observed using Transwell cell migration system. The effect of siRNA-RRM2 on the tumor growth was determined in nude mice. RESULTS: The mRNA and protein levels of RRM2 were higher in MCF-7 cells than those in MCF-10A cells. siRNA-RRM2 down-regulated the expression of RRM2 in MCF-7 cells in a time-and concentration-dependent manner. The results of CCK-8 assay showed that siRNA-RRM2 inhibited the proliferation ability of MCF-7 cells, but not that of MCF-10A cells. The results of Transwell assay indicated that siRNA-RRM2 inhibited the migration ability of MCF-7 cells. siRNA-RRM2 also inhibited the tumor growth in nude mice. CONCLUSION: RRM2 overexpression is associated with the breast cancer proliferation and migration. Suppression of RRM2 function is a potential therapeutic strategy for treating breast cancer.     

Responses of cucumber plant to NH4 and NO3 nutrition: The relative addition rate technique vs. cultivation at constant nitrogen concentration

Different N sources (NO₃⁻, NH₄⁺, or NH₄NO₃) at different relative addition rates (RAR) were supplied to cucumber (Cucumis sativus L.), a species sensitive to NH₄⁺ toxicity. For comparison, cucumber plants were also grown at constant concentrations of 1 and 5 mM NH₄⁺ or 5 mM NO₃⁻. The fresh weight of NH₄⁺-fed plants at RAR 0.15 and RAR 0.25 day⁻¹ was similar to that of NO₃⁻-fed plants, while at RAR 0.35 or RAR 0.45 day⁻¹ growth reduction occurred. When available as a constant concentration, NH₄⁺ decreased plant growth at 5 mM. It is concluded that at low rates of N supply the relative addition rate technique can be used for growing cucumber plants with NH₄⁺ as sole N source without deleterious effects.     

苹果多酚-壳寡糖微胶囊的制备表征及释放特性

为了有效提高未熟苹果多酚（apple polyphenols,APP）和壳寡糖（chitooligosaccharides,COS）多功能协调效应,该研究采用喷雾干燥法研制未成熟的苹果多酚-壳寡糖微胶囊（apple polyphenols-chitooligosaccharides microcapsule,APCM）,并测定了APCM的微胶囊粒度和分布,以及结构表征,并评价了模拟胃肠道消化模型对总多酚（total phenolic content,TPC）释放和健康益处功能的影响。激光粒度分析结果表明,APCM的平均粒径为32.98μm。跨度值最小为1.19,这意味着APCM比COS和APP更均匀、颗粒度更小。APP在1 237和1 194cm-1处观察到了清晰的峰形,在APCM中同一位置处未观察到。但是,APCM与APP具有相似的吸收带,这意味着APP与COS也可能通过范德华力和分子间氢键的方式形成APCM。模拟胃肠消化模型结果表明,APCM中多酚的释放发生在60 min以内。在模拟胃液消化系统（simulated gastric fluid,SGF）处理中,APCM释放的TPC从25.6%到76.5%不等,而在模拟肠液消化系统（simulated intestinal fluid,SIF）持续处理中,TPC释放量达到31.3%到97.6%。体外抗氧化活性和活性氧（reactive oxygen species,ROS）清除活性结果表明,相比与APP和COS,APCM对抗氧化能力指数、清除DPPH自由基、铁离子还原抗氧化力、?OH清除活性、O2?-清除活性和H2O2清除活性表现出更出色的清除自由基活性。此外,与APP或COS相比,APCM不仅表现出更高的糖还原酶抑制活性（P<0.05）,而且具有更好的血管紧张素I转换酶（Angiotensin I converting enzyme,ACE）抑制活性（P<0.05）。结果表明,APCM今后可在功能性食品或药物领域更大的研发潜力。