Fire and Pinus mugo Turra communities in the western Alps (Susa Valley, Italy) during the Lateglacial-Holocene transition: an evidence of refugia area

In western Italian Alps, small distinct populations of Pinus mugo Turra raise some questions concerning its ecological status and dynamics in the occidental Alps. This note present new palaeobotanical data based on cone imprints of Pinus mugo, identified in travertine systems located in the Val di Susa and dated back to the Late Dryas (11506+/-66 BP) and the Early Holocene (10145+/-225 et 9475+/-670 BP). Heliophilous species and charcoal fragments were also identified, testifying to the oldness of wildfires in this region. The data support the hypothesis that this zone was a refuge area of this pine during the last glaciation. Here we discuss about the postglacial dynamics of the Pinus mugo in the occidental Alps.     

Plasmolytic behavior of the donor cell may affect protoplast response

Protoplast donor tissues (leaves of shoots in culture) from a herbaceous plant ( Solanum etuberosum ) and two woody species ( Populus alba × P. grandidentata cv. Crandon and Betula platyphylla szechuanica ) were compared during plasmolysis in a range of osmotic agents and potentials. Cells from both Solanum and Populus , species proven to be amenable to protoplast division and regeneration, plasmolyzed readily at higher osmotic potentials than cells from Betula , a species recalcitrant to prolonged culture after protoplast isolation. Betula leaf mesophyll cells exhibited persistent membrane-to-wall attachments and many failed to plasmolyze even under extreme osmolarity. Although their leaves exhibited similar photosynthetic rates, photosynthetic capacity was lost from Betula protoplasts upon isolation, and retained by Solanum protoplasts. Differential stress after isolation was not detectable through vital staining, but only Solanum and Populus gave both high protoplast yields and high plating efficiencies in continued culture.     

异戊二烯合成酶(IspS)在大肠杆菌中的表达及其产异戊二烯的研究

将来源于银白杨的异戊二烯合成酶基因按照大肠杆菌密码子偏爱性进行优化,克隆到表达载体pACYCDu-et-1上,在大肠杆菌BL21(DE3)中异源表达,采用镍柱亲和层析纯化重组蛋白并测定其异戊二烯合成酶活性,通过摇瓶发酵实验对重组菌产异戊二烯进行进一步研究。结果显示:银白杨异戊二烯合成酶在大肠杆菌中能够高效表达,经过镍柱纯化后,电泳检测到特异性表达条带;该重组异戊二烯合成酶能够催化异戊二烯的合成,重组菌的异戊二烯产量可达到60μg/L。     

The Early Holocene treeline in the southern French Alps: new evidence from travertine formations

Aims The present paper concerns the analysis of macro‐remains (plant imprints) from high altitude travertine deposits dating back to the early Holocene (9800 BP ). Our results allow us to discuss treeline location and ecology, and to supplement previous data based on pollen from natural sediments and charcoal from natural soil. Location The travertine under study is located in the Queyras massif, in the southern French Alps, along the Italian border. The site is situated on a south‐facing slope. Methods The travertine deposit has been dated by ²³⁰Th/²³⁴U. Taxonomic identification of plant imprints was achieved by comparison of the morphology of fossil specimens with extant material. Results Imprints of Pinus uncinata (cones and needles), broad‐leaved trees (Betula cf. pubescens, Populus tremula and Salix spp.), and unidentified trunks have been found. The plant assemblage records the existence at a high altitude (2200 m) of shade‐intolerant vegetation at around 9800 BP. Our data indicate that the treeline limit was at least 100 m higher than previously thought. The morphological features of the travertine, the plant assemblage and trunk diameters indicate that during the travertinization process, vegetation around the site was probably dense with tall upright trees. Main conclusions Our data show that Pinus uncinata and broad‐leaved trees developed at 2200 m, while regional pollen analyses locate the treeline at lower altitudes. Different research methods appear to provide different results. Around 9800 BP tree regeneration and growth were made possible up to at least 2200 m a.s.l., probably as a result of warmer and wetter summers. Warmer conditions are inferred from the predicted increase in incoming solar radiation based on calculated orbital variations, and wetter conditions are inferred from the build‐up of the travertine.     

新疆阿尔泰山前平原河谷林植被类型

 在新疆阿尔泰地区山前平原,沿河谷发育着带状的、以杨属树种为主的森林。本文将该河谷林划分为8个群系和16个群丛组,并作了较详细的描述。所记载的杨属种类有苦杨、银白杨、银灰杨、黑杨、额河杨、胡杨和灰胡杨等7种,此外还有疣枝桦、尖果沙枣以及柳属的几个树种(白柳、三蕊柳等)。河谷林出现在半荒漠、荒漠等地带性植被的包围中,无疑是河谷特殊生境的产物,它对河谷环境和农牧业发展有重要意义。     

Leaf litter breakdown in a Mediterranean stream characterised by travertine precipitation

1. Breakdown of four leaf species ( Platanus orientalis , Populus nigra , Salix atrocinerea , Rubus ulmifolius ) was studied in a Mediterranean second-order stream characterised by abundant travertine precipitation, a history of fire in its catchment, and a recently revegetated alluvial corridor.
2. Compared to breakdown rates reported in the literature for congeneric species, breakdown of the four species was slow (k = 0.0024–0.0069 day⁻¹ for the tree species, and 0.0103 and 0.0111 day⁻¹ for Rubus ), in spite of high water temperatures, indicating that the travertine layer that quickly covered submerged leaves impeded decomposer activity and physical fragmentation losses.
3. Breakdown rates nevertheless differed between leaf species in a predictable manner, suggesting that the observed mass loss was largely due to biological processes.
4. The observed tendency towards increasing leaf nitrogen and phosphorus concentrations during breakdown suggests that microorganisms were actively involved in leaf breakdown; however, this interpretation must be viewed with caution because of potentially confounding effects by nutrients contained in the travertine layer.
5. Leaf breakdown of the three indigenous species was faster than that of the exotic species P. orientalis . Due to the recalcitrance of its leaves, the frequent use of Platanus in revegetation schemes following the destruction of indigenous vegetation by fire, exacerbates the negative effect of travertine precipitation on leaf breakdown and, by extension, energy flow in Mediterranean karst streams.     

温度变化下银白杨叶片中线粒体呼吸对光合作用和异戊二烯释放的影响

温度的升高增加了银白杨叶片异戊二烯的释放水平;随着温度的升高,线粒体呼吸速率则有所下降。用线粒体呼吸途径的抑制剂处理叶片能够增加叶片异戊二烯的释放水平;然而,同样的处理对光系统II叶绿素荧光参数并没有显著性的影响,并降低了叶片的光合速率。基于以上结果,本文认为在温度上升时,异戊二烯的释放可能并不依赖于光合作用,而线粒体呼吸的上游底物流向异戊二烯的合成路径可能促进了温度上升时异戊二烯释放的增加。     

山新杨LTP家族基因生物信息学及表达模式分析

以山新杨（Populus davidiana×P. alba var. pyramidalis）LTP家族基因为研究对象,初步分析该家族基因的序列特征和表达模式,筛选材性和抗性相关PdbLTP基因,为LTP基因的分子调控机制研究及林木遗传改良提供候选基因。通过蛋白性质分析、多序列比对分析、进化树分析初步分析LTP家族基因的序列特征。利用荧光定量PCR（qRT-PCR）分析重力、NaCl及PEG胁迫处理下山新杨LTP家族基因的表达模式。查找获得8条 PdbLTP基因序列,2条亚家族PdbGLTP基因序列。CDS序列长度在294~396 bp。LTP家族蛋白为疏水性蛋白且具有8个半胱氨酸的保守结构。qRT-PCR结果显示,PdbLTP1、PdbLTP3、PdbLTP5、PdbLTP7基因在应拉木中表达上调;PdbLTP1、PdbLTP2、PdbLTP3、PdbLTP5基因在茎中表达量最高;除PdbLTP5外,其它基因均受盐胁迫诱导;PdbLTP1、PdbLTP2、PdbLTP3、和PdbLTP5受干旱胁迫诱导。PdbLTP基因家族成员在调控山新杨木质部发育和抵抗非生物胁迫中发挥作用。     

转基因金叶银中杨叶色及生长变异分析

转PaGLK基因银中杨抑制表达株系叶绿素含量显著降低,叶片呈现黄色（命名为金叶银中杨）,以转PaGLK基因的银中杨为材料,测定其叶色参数和叶绿素含量的时序变化规律、分析生长特性。结果显示,转PaGLK基因的银中杨使叶片颜色发生改变,抑制表达株系整个生长期叶绿素含量显著低于WT（P<0.05）,叶色亮度显著高于WT（P<0.05）,并且在生长发育期叶片一直呈现深黄绿色。抑制表达株系中的Y2速生期内苗高日生长量（GD）高于对照株系,苗期株高不受影响。而过表达转基因银中杨的当年高生长都显著低于对照株系 （P<0.05）,其速生期内苗高日生长量均值（GD）也低于对照株系,其均值为对照株系的22.19%。PaGLK抑制表达株系在城市园林绿化具有潜在的应用价值。     

新疆杨愈伤组织原生质体的游离与纯化

目的:以愈伤组织为材料,研究新疆杨原生质体的游离、纯化。方法:以新疆杨愈伤组织为材料,采用简单试验设计和方差分析方法,对新疆杨原生质体游离的影响因素进行研究,并利用二乙酸荧光素染色法观察原生质体活力。结果:适宜新疆杨愈伤组织原生质体游离的较适宜条件是:CPW+2.0%纤维素酶R-10+1.0%离析酶R-10+1.0%果胶酶Y-23+0.6 mol/L甘露醇,酶解温度27℃,酶解时间8 h。在此条件下,原生质体产量达8.5×106个/(g.FW),活力达83.6%。原生质体纯化可采用蔗糖等密度离心法,较适蔗糖浓度为30%。结论:研究筛选出的酶解因素组合与等密度离心条件较适宜新疆杨愈伤组织原生质体的游离和纯化。     

一种优化的胡杨高效多重（12重）SSR体系

微卫星多重PCR方法是一种非常经济并且高通量的基因分型技术。本研究在耐干旱、盐碱的胡杨（Populus euphratica）中开发出一套荧光标记的12重微卫星工作体系。该体系包含12条表达序列标签微卫星（EST-SSR）引物,其中3条设计于NCBI,另外9条设计于二代的转录组序列。利用该多重微卫星体系可在单一的PCR反应体系中成功扩增出12条表达序列标签的微卫星短序列片段。并在胡杨的3个自然居群96个个体中对该体系进行了验证,结果显示该体系具有很高的稳定性及多样性。同时,在杨属的5个派7个种中对其通用性进行了检验,显示这些引物具有很高的通用性,成功扩增率为79％。本研究中提供的12重多重PCR结合本实验已经公开发表的2个8重体系对揭示胡杨及其他杨树的进化历史具有重要的作用。最后,本研究认为引物的选择,扩增效率,哑等位基因的检测是多重体系开发过程中最为关键的步骤。     

一种优化的胡杨高效多重 (12重) SSR体系

微卫星多重PCR方法是一种非常经济并且高通量的基因分型技术。本研究在耐干旱、盐碱的胡杨（Populus euphratica）中开发出一套荧光标记的12重微卫星工作体系。该体系包含12条表达序列标签微卫星（EST SSR）引物,其中3条设计于NCBI,另外9条设计于二代的转录组序列。利用该多重微卫星体系可在单一的PCR反应体系中成功扩增出12条表达序列标签的微卫星短序列片段,并在胡杨的3个自然居群96个个体中对该体系进行了验证,结果显示该体系具有很高的稳定性及多样性。同时,在杨属的5个派7个种中对其通用性进行了检验,显示这些引物具有很高的通用性,成功扩增率为79%。本研究中提供的12重多重PCR结合本实验已经公开发表的2个8重体系对揭示胡杨及其他杨树的进化历史具有重要的作用。最后,本研究认为引物的选择,扩增效率,哑等位基因的检测是多重体系开发过程中最为关键的步骤。     

High Throughput SSR Multiplex Kits (12 plex) for Euphrates’ Poplar,Populus euphratica (Salicaceae)

Multiplex PCR of microsatellite is a cost effective and high throughput technique of genotyping. We developed a new 12 plex PCR kit for Populus euphratica, the only tree species in desert area ranging from Western China to Mediterranean coast. Three primers were designed for the expressed sequence tags (ESTs) sequences from the NCBI database and the other nine primers were designed based on the EST sequences of Peuphratica obtained by Solexa. The multiplex kit was tested by 96 samples from three natural populations. The results showed sufficient amplification stability and high polymorphism. All the 12 loci used in this kit showed a high transferability (79%) in other seven species from five sections of the genus. The new 12 plex kit combined with the two eight multiplex kits we had developed in previous studies, should be useful to reveal the genetic mechanism and evolution history of the Peuphratica and related species. During the research, we found that primers selection, amplification efficiency, null allele detection are the essential parts of the multiplex kit development.     

Barrier to gene flow between two ecologically divergent Populus species, P. alba (white poplar) and P. tremula (European aspen): the role of ecology and life history in gene introgression

The renewed interest in the use of hybrid zones for studying speciation calls for the identification and study of hybrid zones across a wide range of organisms, especially in long-lived taxa for which it is often difficult to generate interpopulation variation through controlled crosses. Here, we report on the extent and direction of introgression between two members of the "model tree" genus Populus: Populus alba (white poplar) and Populus tremula (European aspen), across a large zone of sympatry located in the Danube valley. We genotyped 93 hybrid morphotypes and samples from four parental reference populations from within and outside the zone of sympatry for a genome-wide set of 20 nuclear microsatellites and eight plastid DNA restriction site polymorphisms. Our results indicate that introgression occurs preferentially from P. tremula to P. alba via P. tremula pollen. This unidirectional pattern is facilitated by high levels of pollen vs. seed dispersal in P. tremula (pollen/seed flow = 23.9) and by great ecological opportunity in the lowland floodplain forest in proximity to P. alba seed parents, which maintains gene flow in the direction of P. alba despite smaller effective population sizes (N(e)) in this species (P. alba N(e)c. 500-550; P. tremula N(e)c. 550-700). Our results indicate that hybrid zones will be valuable tools for studying the genetic architecture of the barrier to gene flow between these two ecologically divergent Populus species.     

The essential oil of Lippia alba: analysis of samples from French overseas departments and review of previous works

This paper contains new data on the chemical composition of the essential oil of Lippia alba (Mill.) N. E. Brown, as well as an overview of the available literature. Although the composition of the essential oil of this species is well-documented, discrepancies between the reported results suggest that many chemotypes and morphotypes exist. The analysis of essential oils obtained from the leaves of samples from three different locations in the French Overseas Departments (French Guiana, Martinique, and two different places in Guadeloupe) have shown that the composition of each one is quite different. This new data, along with a review and discussion of published studies, enabled us to establish seven distinct chemotypes. Possible connections between these chemotypes and morphotypes already described were also investigated.     

PtaRHE1, a Populus tremula × Populus alba RING‐H2 protein of the ATL family,has a regulatory role in secondary phloem fibre development

REALLY INTERESTING NEW GENE (RING) proteins play important roles in the regulation of many processes by recognizing target proteins for ubiquitination. Previously, we have shown that the expression of PtaRHE1, encoding a Populus tremula × Populus alba RING‐H2 protein with E3 ubiquitin ligase activity, is associated with tissues undergoing secondary growth. To further elucidate the role of PtaRHE1 in vascular tissues, we have undertaken a reverse genetic analysis in poplar. Within stem secondary vascular tissues, PtaRHE1 and its corresponding protein are expressed predominantly in the phloem. The downregulation of PtaRHE1 in poplar by artificial miRNA triggers alterations in phloem fibre patterning, characterized by an increased portion of secondary phloem fibres that have a reduced cell wall thickness and a change in lignin composition, with lower levels of syringyl units as compared with wild‐type plants. Following an RNA‐seq analysis, a biological network involving hormone stress signalling, as well as developmental processes, could be delineated. Several candidate genes possibly associated with the altered phloem fibre phenotype observed in amiRPtaRHE1 poplar were identified. Altogether, our data suggest a regulatory role for PtaRHE1 in secondary phloem fibre development.     

The Atlantic-Mediterranean watershed, river basins and glacial history shape the genetic structure of Iberian poplars

Recent phylogeographic studies have elucidated the effects of Pleistocene glaciations and of Pre-Pleistocene events on populations from glacial refuge areas. This study investigates those effects in riparian trees (Populus spp.), whose particular features may convey enhanced resistance to climate fluctuations. We analysed the phylogeographic structure of 44 white (Populus alba), 13 black (Populus nigra) and two grey (Populus x canescens) poplar populations in the Iberian Peninsula using plastid DNA microsatellites and sequences. We also assessed fine-scale spatial genetic structure and the extent of clonality in four white and one grey poplar populations using nuclear microsatellites and we determined quantitative genetic differentiation (Q(ST) ) for growth traits in white poplar. Black poplar displayed higher regional diversity and lower differentiation than white poplar, reflecting its higher cold-tolerance. The dependence of white poplar on phreatic water was evidenced by strong differentiation between the Atlantic and Mediterranean drainage basins and among river basins, and by weaker isolation by distance within than among river basins. Our results suggest confinement to the lower river courses during glacial periods and moderate interglacial gene exchange along coastlines. In northern Iberian river basins, white poplar had lower diversity, fewer private haplotypes and larger clonal assemblies than in southern basins, indicating a stronger effect of glaciations in the north. Despite strong genetic structure and frequent asexual propagation in white poplar, some growth traits displayed adaptive divergence between drainage and river basins (Q(ST) >F(ST)), highlighting the remarkable capacity of riparian tree populations to adapt to regional environmental conditions.     

Plants utilize isoprene emission as a thermotolerance mechanism

Isoprene is a volatile compound emitted from leaves of many plant species in large quantities, which has an impact on atmospheric chemistry due to its massive global emission rate (5 x 10(14) carbon g year(-1)) and its high reactivity with the OH radical, resulting in an increase in the half-life of methane. Isoprene emission is strongly induced by the increase in isoprene synthase activity in plastids at high temperature in the day time, which is regulated at its gene expression level in leaves, while the physiological meaning of isoprene emission for plants has not been clearly demonstrated. In this study, we have functionally overexpressed Populus alba isoprene synthase in Arabidopsis to observe isoprene emission from transgenic plants. A striking difference was observed when both transgenic and wild-type plants were treated with heat at 60 degrees C for 2.5 h, i.e. transformants revealed clear heat tolerance compared with the wild type. High isoprene emission and a decrease in the leaf surface temperature were observed in transgenic plants under heat stress treatment. In contrast, neither strong light nor drought treatments showed an apparent difference. These data suggest that isoprene emission plays a crucial role in a heat protection mechanism in plants.     

Evaluation of qPCR reference genes in two genotypes of Populus for use in photoperiod and low-temperature studies

ABSTRACT: BACKGROUND: Quantitative PCR (qPCR) is a widely used technique for gene expression analysis. A common normalization method for accurate qPCR data analysis involves stable reference genes to determine relative gene expression. Despite extensive research in the forest tree species Populus, there is not a resource for reference genes that meet the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) standards for qPCR techniques and analysis. Since Populus is a woody perennial species, studies of seasonal changes in gene expression are important towards advancing knowledge of this important developmental and physiological trait. The objective of this study was to evaluate reference gene expression stability in various tissues and growth conditions in two important Populus genotypes (P. trichocarpa "Nisqually 1" and P. tremula X P. alba 717 1-B4) following MIQE guidelines. RESULTS: We evaluated gene expression stability in shoot tips, young leaves, mature leaves and bark tissues from P. trichocarpa and P. tremula. x P. alba grown under long-day (LD), short-day (SD) or SD plus low-temperatures conditions. Gene expression data were analyzed for stable reference genes among 18S rRNA, ACT2, CDC2, CYC063, TIP4-like, UBQ7, PT1 and ANT using two software packages, geNormPLUS and BestKeeper. GeNormPLUS ranked TIP4-like and PT1 among the most stable genes in most genotype/tissue combinations while BestKeeper ranked CDC2 and ACT2 among the most stable genes. CONCLUSIONS: This is the first comprehensive evaluation of reference genes in two important Populus genotypes and the only study in Populus that meets MIQE standards. Both analysis programs identified stable reference genes in both genotypes and all tissues grown under different photoperiods. This set of reference genes was found to be suitable for either genotype considered here and may potentially be suitable for other Populus species and genotypes. These results provide a valuable resource for the Populus research community.     

白杨杂种三倍体小孢子母细胞减数分裂及花粉形态观察

通过醋酸洋红压片等方法观察毛新杨×银腺杨杂种三倍体小孢子母细胞减数分裂及花粉形态,以探讨杂种三倍体雄配子的育性及其细胞学机制.结果显示:(1)在小孢子母细胞减数分裂过程中可观察到部分染色体提前分向两极、落后染色体、微核等一系列染色体异常行为,表明该三倍体存在染色体的高度不平衡性.(2)在减数第二次分裂过程中存在大量胞质分裂提前现象;减数分裂产物中发现有少量二分体、三分体的存在,同时毛新杨×银腺杨杂种三倍体花粉粒的直径变化范围为22.6～62.6 μm,呈现双峰分布,由此推测有一定数量的具可育性的未减数花粉产生.