Constitutive Nuclear Localization of an Alternatively Spliced Sirtuin-2 Isoform

Sirtuin-2 (SIRT2), the cytoplasmic member of the sirtuin family, has been implicated in the deacetylation of nuclear proteins. Although the enzyme has been reported to be located to the nucleus during G₂/M phase, its spectrum of targets suggests functions in the nucleus throughout the cell cycle. While a nucleocytoplasmic shuttling mechanism has been proposed for SIRT2, recent studies have indicated the presence of a constitutively nuclear isoform. Here we report the identification of a novel splice variant (isoform 5) of SIRT2 that lacks a nuclear export signal and encodes a predominantly nuclear isoform. This novel isoform 5 fails to show deacetylase activity using several assays, both in vitro and in vivo, and we are led to conclude that this isoform is catalytically inactive. Nevertheless, it retains the ability to interact with p300, a known interaction partner. Moreover, changes in intrinsic tryptophan fluorescence upon denaturation indicate that the protein is properly folded. These data, together with computational analyses, confirm the structural integrity of the catalytic domain. Our results suggest an activity-independent nuclear function of the novel isoform.     

The Plant Host Can Affect the Encapsidation of Brome Mosaic Virus (BMV) RNA: BMV Virions Are Surprisingly Heterogeneous

Brome mosaic virus (BMV) packages its genomic and subgenomic RNAs into three separate viral particles. BMV purified from barley, wheat, and tobacco have distinct relative abundances of the encapsidated RNAs. We seek to identify the basis for the host-dependent differences in viral RNA encapsidation. Sequencing of the viral RNAs revealed recombination events in the 3′ untranslated region of RNA1 of BMV purified from barley and wheat, but not from tobacco. However, the relative amounts of the BMV RNAs that accumulated in barley and wheat are similar and RNA accumulation is not sufficient to account for the difference in RNA encapsidation. Virions purified from barley and wheat were found to differ in their isoelectric points, resistance to proteolysis, and contacts between the capsid residues and the RNA. Mass spectrometric analyses revealed that virions from the three hosts had different post-translational modifications that should impact the physiochemical properties of the virions. Another major source of variation in RNA encapsidation was due to the purification of BMV particles to homogeneity. Highly enriched BMV present in lysates had a surprising range of sizes, buoyant densities, and distinct relative amounts of encapsidated RNAs. These results show that the encapsidated BMV RNAs reflect a combination of host effects on the physiochemical properties of the viral capsids and the enrichment of a subset of virions. The previously unexpected heterogeneity in BMV should influence the timing of the infection and also the host innate immune responses.     

箱式气体交换观测系统及其在植物生态系统气体交换研究中的应用

基于箱式法构建的箱式气体交换观测系统是植物生态系统碳水循环研究的常用方法,其在土壤和植物组织尺度的气体交换研究中的作用尤为重要.本文根据箱式气体交换观测系统的气路结构,对闭路、半闭路、开路和半开路系统的原理和计算方法进行了详细总结;汇总了目前常用的商业箱式气体交换观测系统,并回顾了自制系统的研制和应用历程;最后简要探讨了箱式气体交换观测系统存在的问题及其改进方式.     

西双版纳社区村民对亚洲象保护廊道建设的认知与态度

采用条件价值评估法(CVM),2007年11月至2008年3月,调查分析了地处西双版纳的2条亚洲象保护廊道内5个村寨196户村民对廊道建设的认知与态度.结果表明：研究区80.61%的村民愿意有条件地支持廊道建设;影响村民支持意愿的因素包括村民的文化程度、人均年收入以及村民就亚洲象保护、人象关系、廊道利用方式和受益群体的认知;该区村民对亚洲象的保护意识、廊道的利用方式和受益群体对村民支持意愿的影响较大,其影响系数分别为0.231、0.236和-0.304.拥有土地使用权的社区村民在生物保护廊道建设中扮演着重要角色,有效的廊道设计与规划必须深入了解社区村民对生物保护廊道的认知和态度,并获得他们的支持和参与.     

中国典型丘陵区人口密集乡村景观的土壤碳氮磷分布特征

基于IKONOS高分辨率(1 m)卫星遥感图,根据生态立地分层分类规则,评价了四川盆地、江南山地和华南山地等典型丘陵区人口密集的乡村景观结构对0～30 cm土壤有机碳(SOC)、全氮(TN)和全磷(TP)密度及储量的影响.结果表明：SOC密度的面积加权平均值为江南山地丘陵(2.72±0.76 kg·m^-2) > 华南山地丘陵(2.65±0.73 kg·m^-2)>四川盆地丘陵(2.15±0.57 kg·m^-2);TN密度的面积加权平均值为江南山地丘陵(0.28±0.06 kg·m^-2) >四川盆地丘陵(0.27±0.06 kg·m^-2) >华南山地丘陵(0.21±0.06 kg·m^-2);TP密度的面积加权平均值为四川盆地丘陵(0.19±0.04 kg·m^-2) >江南山地丘陵(0.11±0.03 kg·m^-2)>华南山地丘陵(0.08±0.04 kg·m^-2).四川盆地、江南山地和华南山地丘陵SOC、TN和TP储量最高的生态立地类型分别为小规模1年生旱地作物、两季水田和斜坡次生阔叶疏林.SOC和TN密度均以水田或林地最高,而以低覆盖度的挖掘地和山顶旱地最低,TP密度的分布较为复杂.细微尺度的生态立地水平分析可以较好地反映出丘陵区人口密集乡村景观地区的生态结构和SOC、TN、TP的分布情况.     

黄土丘陵区小流域土地利用对土壤有机碳和全氮的影响

通过野外调查和室内分析,研究了黄土丘陵沟壑区燕沟流域农地、果园、林地和草地0～20cm表层土壤的有机碳(SOC)和全氮(TSN)积累特征.结果表明:该区SOC含量平均值为7·56g·kg-1,TSN平均值为0·71g·kg-1.其中,农地SOC和TSN平均值分别为4·67和0·48g·kg-1,且梯田较低,川坝地较高.与农地相比,果园SOC(4·33g·kg-1)和TSN(0·46g·kg-1)平均值略有降低,草地较高.林地SOC和TSN平均值较农地高117·7%和89·4%.该区SOC和TSN含量的变异系数为69·7%和58·4%,以林地最大(62·8%和54·5%),草地和农地次之,果园最小(18·0%和22·9%).土壤C/N依果园、农地、草地和林地的顺序递增.该区各类土地利用方式下的SOC和TSN都呈极显著正相关(r=0·9791).黄土丘陵沟壑区基本农田建设和果园建设对SOC和TSN积累作用不明显;退耕还林还草、封山育林等土地利用优化措施明显促进了SOC和TSN的积累.     

半干旱黄土丘陵区垄沟集雨对紫花苜蓿人工草地土壤水分和产草量的影响

研究了黄土丘陵区垄沟集雨技术对紫花苜蓿(Medicago sativa)人工草地生产力以及土壤水分的影响。垄和沟的宽度均为30或60 cm,且垄上覆膜的处理水分利用效率分别比平作对照显著提高了13%和41%。垄和沟的宽度均为30 cm且垄上覆膜的处理4年的干草产量和平作对照无显著差异,而垄和沟的宽度均为60 cm,且垄上覆膜的处理干草产量比平作对照显著提高了41%,并且使紫花苜蓿草地产草高峰期提早了1~2年。垄和沟的宽度均为30或60 cm,且垄面裸露的两个处理产草量比平作对照有不同程度的降低。紫花苜蓿草地生长的第三年,深度为150 cm左右的土层是降水补充和水分消耗的平衡点。所有处理在紫花苜蓿生长4年后,200~500 cm 深度的土壤水分已经接近萎蔫系数。     

棉花临界需氮量动态定量模型

在大田栽培条件下,于江苏南京和河南安阳两个生态区设置棉花氮素水平试验,基于作物临界氮浓度稀释模型和干物质动态累积模型,建立了棉花花后动态临界氮吸收速率、临界氮需求量的定量化模型.结果表明,两生态区的临界最大氮吸收速率均出现在花后42 d,分别为5.3和4.4 kg·hm^-2·d^-1,临界快速氮累积期分别在花后的23～59 d和23～61 d,安阳的最大临界日需氮量明显大于南京.根据模型得到：安阳生态区适宜施氮量在240～360 kg·hm^-2 之间,且360 kg·hm^-2 条件下其氮累积接近临界需求,南京生态区240 kg·hm^-2施氮量的氮累积与临界值相近.两区域基肥施用量分别占总施肥量的26%和27%,且适宜的追肥时间应在花后22 d左右.由于模型的建立是基于不同氮处理试验,有合理可靠的生理依据,为定量确定不同气候区域的动态施肥量提供了理论依据.     

长三角地区大棚避雨栽培下不同生态适应型葡萄的光合特性

研究了长江三角洲地区大棚避雨覆盖栽培下葡萄光合生理生态特性的变化规律.结果表明,不论是晴天还是阴天,避雨覆盖都显著削弱了大棚内的光合有效辐射（PFD）,但对气温（T_a）、大气水汽压（V_p）和蒸腾速率（T_r）无明显影响.避雨覆盖栽培使美人指与藤稔葡萄品种的叶片厚度分别下降了28.6%和18.4%、比叶鲜重分别下降了13.1%和11.6%、叶片总叶绿素(Chl)含量与表观量子效率（AQY）略有增加,但Chla、Chlb含量及Chla/Chlb比值与对照无显著差异.晴天时,避雨覆盖栽培使美人指和藤稔品种的净光合速率（P_n）日均值分别下降18.7%和13.1％、P_n日积分值分别下降17.2%和11.9％、水分利用效率（WUE）分别下降26%和36.9％、气孔导度（G_s）则分别增加76.8%和100.8%;阴天时,避雨覆盖栽培使美人指和藤稔品种的P_n日均值分别下降48.7%和33.5％、P_n日积分值分别下降34.0%和29.8％、WUE分别下降69.2%和67.7％、G_s分别增加178.0%和85.1%.美人指品种的生理、光合指标的变幅比藤稔品种大,且阴天条件下差异更显著,表明两品种的生态适应性有明显差异.