Arsenate reductase activity in roots from the arsenic hyperaccumulator Pteris vittata utilizes both glutathione and dithiothreitol as reductants

Abstract

The role of glutathione and dithiothreitol as reductants supporting arsenate reductase activity in root extract from the arsenic hyperaccumulator Pteris vittata was examined. The two reductants in combination enhanced arsenate reduction in vitro more than glutathione alone. The implications of these results for in vivo arsenate reduction are discussed.     

Apogamous sporophyte formation in a fernPteris multifida and its characteristics

When spores of the fern,Pteris multifida, were aseptically cultured in the dark, sporophytic plants were apogamously induced. The plants have been subsequently grown in pots until the development of leaves with many sporangia for observations of meiotic characteristics in their sporocytes. The sporophytic plants originated from spores were estimated to be haploid, and the estimation was supported by abnormal meiosis in sporocytes and the absence of mature spores, but some chromosomes (n=58) formed bivalents in the meiotic process.     

川西高原不同坡向云、冷杉树轮对快速升温的响应差异

在川西高原松潘县二道海林区的东南坡、西北坡和扎日寺林区的东坡用零信号法建立4条云、冷杉树轮年表,通过年轮 气候响应分析、多因素方差分析等方法研究不同坡向树木生长对快速升温的响应差异.结果表明： 快速升温(1980年)后,东坡紫果云杉生长显著加速(0.011 a^-1),而西北坡紫果云杉生长则显著降低(-0.006 a^-1),东南坡紫果云杉和西北坡岷江冷杉生长降低,但不显著.随着快速升温,不同坡向云、冷杉径向生长与气候因子的关系均出现显著变化.快速升温后,生长季温度对东坡紫果云杉径向生长的促进作用显著增加,对东南坡和西北坡紫果云杉径向生长的抑制作用也显著增加,但生长季温度对西北坡岷江冷杉径向生长的影响在升温前后变化不明显.5月降水量对东坡紫果云杉径向生长由升温前的抑制作用变为升温后的显著促进作用,而对东南坡和西北坡紫果云杉径向生长的抑制作用显著增加,5月降水量对西北坡岷江冷杉径向生长的影响在升温前后变化不明显.树轮与帕尔默干旱指数响应分析表明,快速升温后,不同坡向的土壤湿度变化是造成树轮响应差异的重要原因.多因素方差分析表明,坡向与温度、降水的综合作用是影响紫果云杉径向生长的重要因素.因此,在模拟预测树木生长对气候变暖的响应动态时,应考虑不同坡向与温度、降水的综合作用.     

北大西洋大青鲨种群统计分析

大青鲨是金枪鱼延绳钓渔业中最主要的兼捕鱼种,在海洋食物网中属于顶端物种,在海洋生态系统中处于重要地位.由于数据限制,传统的资源评估方法很难准确描述大青鲨的资源动态.本研究基于大青鲨的生活史参数,应用种群统计分析法评估大青鲨的种群参数和资源状态,并探讨了内禀增长率为0时对应的临界捕捞死亡系数F_c与开捕年龄t_c的关系.结果表明： 未开发状态下,大青鲨存活率为0.719～0.820;大青鲨的内在瞬时增长率(r₀)为0.250～0.381,种群倍增时间(t_x2)为1.819～2.773年,种群的净繁殖力(R₀)为6.600～22.255,世代间期时间(G)为8.498～〖JP2〗10.162年,种群资源状态良好.生活史参数的敏感性检验显示,大青鲨初始年龄的自然死亡系数、种群性成熟年龄及寿命的不确定性对种群统计参数的意义影响不大;临界捕捞死亡系数伴随开捕年龄的增大而增大,当t_c≥5时,F_c值与t_c无显著相关关系.     

低温和光周期对西藏飞蝗体内物质的影响

为探讨西藏飞蝗对环境的适应机制,本文采用全光照(24L/0D)、全黑暗(0L/24D)与5 ℃低温相结合的试验处理,研究了低温和光照胁迫对西藏飞蝗体内物质含量变化的影响.结果表明： 西藏飞蝗虫体脂肪含量以未经低温胁迫的全光照处理最高,达到11.8%.经低温和黑暗处理的西藏飞蝗虫体脂肪含量最低,为4.7%.经低温胁迫处理后虫体的海藻糖、甘露醇以和山梨醇含量显著高于未经低温胁迫处理.虫体糖原含量以未经低温胁迫的全光照处理最高,达6.40 mg·g^-1.低温和黑暗处理还诱导丙氨酸、谷氨酸、赖氨酸和苯丙氨酸累积,促使西藏飞蝗体内多种氨基酸、甘油、小分子碳水化合物积累,糖原和脂肪含量降低.     

Biological and nutritional aspects involved in fern multiplication

Gametophytes of several species of ferns were mechanically triturated and the resulting homogenates cultured in vitro for propagation purposes. Differences in the time period from spore culture to sporophyte development were perceivable between species. For those species with a fast life cycle and high sporophyte production such as Woodwardia virginica and Dryopteris affinis sp. affinis, homogenization of gametophytes can be considered to be excellent method for propagation, yielding hundreds of sporophytes in a short period of time. Sporophyte formation was inhibited in O. regalis by the succesive application of homogenization to gametophytes regenerated by this technique. The effect of the culture medium composition on fern production was also studied in O. regalis and P. ensiformis gametophytes. In these species, sporophyte formation increased when the gametophytes were cultured in a medium containing water+0.7% agar. Addition of sucrose inhibited gametophyte development and induced their necrosis. The 1/2 dilution of Murashige and Skoog basal medium, without sucrose, favoured leaf expansion in P. ensiformis sporophytes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytofiltration of arsenic-contaminated groundwater using Pteris vittata L.: effect of plant density and nitrogen and phosphorus levels

This field-scale hydroponic experiment investigated the effects of plant density and nutrient levels on arsenic (As) removal by the As-hyperaccumulator Pteris vittata L. (Chinese brake fern). All ferns were grown in plastic tanks containing 30 L of As-contaminated groundwater (130 microg x L(-1) As) collected from South Florida. The treatments consisted of four plant densities (zero, one, two, or four plants per 30 L), two nitrogen (N) concentrations (50% or 100% of 0.25-strength Hoagland solution [HS]), and two phosphorous (P) concentrations (15% and 30% of 0.25 strength HS). While low P was more effective than high P for plant As removal initially, N levels showed little effect. At 15% P, it took 3 wk for the ferns at a plant density of four to reduce As to less than 10 microg L(-1) (USEPA and WHO standard), whereas it took 4-6 wk at plant densities of one or two. For reused ferns, established plants with more extensive roots than "first-time" ferns, a low plant density of one plant/30 L was more effective, reducing As in water to less than 10 microg L(-1) in 8 h. This translates to an As removal rate of 400 microg h(-l) plant(-1), which is the highest rate reported to date. Arsenic-concentration in tanks with no plants as a control remained high throughout the experiment. Using more established ferns supplemented with dilute nutrients (0.25 HS with 25% N and 15% P) with optimized plant density (one plant per 30 L) reduced interplant competition and secondary contamination from nutrients, and can be recommended for phytofiltration of As-contaminated groundwater. This study demonstrated that P. vittata is effective in remediating As-contaminated groundwater to meet recommended standards.     

A comparison of arsenic mobility in Phaseolus vulgaris, Mentha aquatica, and Pteris cretica rhizosphere

The ability of Phaseolus vulgaris, Mentha aquatica, and Pteris cretica to release arsenic (As) species from contaminated soil was tested in rhizobox experiments in three soils differing in their physicochemical parameters and total and mobile As concentration. Relatively low uptake of arsenic by P. vulgaris and M. aquatica resulted in very low and ambiguous changes in rhizosphere soil compared to bulk soil. However, there were observed differences in the distribution of the mobile As portion in soil to individual As species as affected by plant species and/or plantation conditions of these plants. Higher percentage of mobile arsenite in mint rhizosphere seems to be related to more reducing conditions during cultivation of these wetland plants. P. cretica planted in the soils containing between 36 and 1436 mg As kg⁻¹ was able to accumulate between 80 and 500 mg As kg⁻¹ in aboveground biomass. The extractable concentrations of As compounds in rhizosphere soil of P. cretica showed a clear depletion of arsenate (representing more than 90% of extractable arsenic) with the distance from plant roots. However, the As uptake mechanisms, as well as As transformation within hyperaccumulating fern plants, differ substantially from those in higher plants. Therefore the finding of suitable higher plant tolerant to the As soil contamination with good ability to accumulate As in aboveground biomass remains for the further research.     

砷超富集植物蜈蚣草原生质体的分离及其抗砷性分析

蜈蚣草（Pteris vittata）是一种砷超富集植物,能够通过根从土壤中吸收砷,并将其输送至羽叶中富集.为了探索蜈蚣草单个细胞在砷积累和砷抗性中的特性,本文首次通过酶解方法获得了这一砷超富集蕨类植物的原生质体,并研究了原生质体在不同浓度砷胁迫下的生活力.结果显示,蜈蚣草原生质体的抗砷性远高于烟草原生质体的抗砷性,与其整体植株的抗性一致.这为探索砷抗性和超富集机理提供了一个新的研究体系.