Seasonal Changes in the Ultrastructure of the Vascular Cambium in Shoots of Populus tomentosa

Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.

Cambium Networks推出无线宽带点对点连接和多点订阅者模块

全球领先的无线网络解决方案提供商Cambium Networks推出ePMPTMForce190无线宽带模块。在针对点对点无线连接进行配置之后,该系统可以为播放视频、语音和数据应用提供高达200 Mbps的连接。在利用ePMP 2000或ePMP1000接入点（AP）进行点对多点配置之后,Force

Cambium Networks推出Wi-Fi墙壁面板解决方案

全球领先的无线网络解决方案提供商Cambium Networks今天宣布推出新的云管理企业级Wi-Fi墙壁面板接入点cnPilot e430W。该接入点支持802.11ac Wave 2标准,是为酒店、度假村和多住宅单元(MDU)提供连接的最佳解决方案。该接入点安装在墙上,使用多个千兆以太网(Gig E)端口通过托管门户提供室内WiFi和有线端口网络接入。Frontera Consulting联合创始人Drew

Gibberellin promotes cambium reestablishment during secondary vascular tissue regeneration after girdling in an auxin-dependent manner in Populus

Secondary vascular tissue(SVT)development and regeneration are regulated by phytohormones.In this study,we used an in vitro SVT regeneration system to demonstrate that gibberellin(GA)treatment significantly promotes auxin-induced cambium reestablishment.Altering GA content by overexpressing or knocking down ent-kaurene synthase(KS)affected secondary growth and SVT regeneration in poplar.The poplar DELLA gene GIBBERELLIC ACID INSENSITIVE(PtoGAI)is expressed in a specific pattern during secondary growth and cambium regeneration after girdling.Overexpression of PtoGAI disrupted poplar growth and inhibited cambium regeneration,and the inhibition of cambium regeneration could be partially restored by GA application.Further analysis of the PtaDR5:GUS transgenic plants,the localization of PIN-FORMED 1(PIN1)and the expression of auxin-related genes found that an additional GA treatment could enhance the auxin response as well as the expression of PIN1,which mediates auxin transport during SVT regeneration.Taken together,these findings suggest that GA promotes cambium regeneration by stimulating auxin signal transduction.

PtrHB7, a class III HD-Zip Gene, Plays a Critical Role in Regulation of Vascular Cambium Differentiation in Populus

A key question in the secondary growth of trees is how differentiation of the vascular cambium cells is directed to concurrently form two different tissues： xylem or phloem, class III homeodomain-leucine zipper （HD-Zip III） genes are known to play critical roles in the initiation, patterning, and differentiation of the vascular system in the process of primary and secondary growth. However, the mechanism of how these genes control secondary vascular dif- ferentiation is unknown. Here, we show that a Populus class III HD-Zip gene, PtrHB7, was preferentially expressed in cambial zone. PtrHB7-suppressed plants displayed significant changes in vascular tissues with a reduction in xylem but increase in phloem. Transcriptional analysis revealed that genes regulating xylem differentiation were down-regulated, whereas genes regulating phloem differentiation were up-regulated. Correspondingly, PtrHB7 overexpression enhanced differentiation of cambial cells toward xylem cells but inhibited phloem differentiation. PtrHB7 regulation on cambial cell differentiation was associated with its transcript abundance. Together, the results demonstrated that PtrHB7 plays a critical role in controlling a balanced differentiation between secondary xylem and phloem tissues in the process of Populus secondary growth in a dosage-dependent manner.

Vascular Cambium-Localized AtSPDT Mediates Xylem-to-Phloem Transfer of Phosphorus for Its Preferential Distribution in Arabidopsis

During plant growth and development mineral elements are preferentially delivered to different organs and tissues to meet the differential demand. It has been shown that the preferential distribution of mineral nutrients in gramineous plants is mediated by node-based transporters, but the mechanisms of preferential distribution in dicots are poorly understood. Here, we report a distinct mechanism for the preferential distribution of phosphorus (P) in Arabidopsis plants, revealed by detailed functional analysis of AtSPDT/AtSULTR3;4 (SULTR-like P Distribution Transporter), a homolog of rice OsSPDT. Like OsSPDT, AtSPDT is localized at the plasma membrane and showed proton-dependent transport activity for P. Interestingly, we found that AtSPDT is mainly expressed in the rosette basal region and leaf petiole, and its expression is up-regulated by P deficiency. Tissue-specific analysis showed that AtSPDT is mainly located in the vascular cambium of different organs, as well as in the parenchyma tissues of both xylem and phloem regions. Knockout of AtSPDT inhibited the growth of new leaves under low P due to decreased P distribution to those organs. The seed yields of the wild-type and atspdt mutant plants are similar, but the seeds of mutant plants contain – less P. These results indicate that AtSPDT localized in the vascular cambium is involved in preferential distribution of P to the developing tissues, through xylem-to-phloem transfer mainly at the rosette basal region and leaf petiole.

TwoMADS-boxgenes regulate vascularcambium activity and secondary growth by modulating auxin homeostasis in Populus

In trees,stem secondary growth depends on vascular cambium proliferation activity and subsequent cell differentiation,in which an auxin concentration gradient across the cambium area plays a crucial role in regulating the process.However,the underlying molecular mechanismfor the establishment of auxin concentration is not fully understood.In this study,we identified two function-unknown MADS-box genes,VCM1 and VCM2,which are expressed specifically in the vascular cambium and modulate the subcellular homeostasis of auxin.Simultaneous knockdown of both VCM1 and VCM2 enhanced vascular cambium proliferation activity and subsequent xylem differentiation.Overexpression of VCM1 suppressed vascular cambium activity and wood formation by regulating PIN5 expression,which tuned the soluble auxin concentration in the vascular cambium area.This study reveals the role of VCM1 and VCM2 in regulating the proliferation activity of the vascular cambium and secondary growth by modulating the subcellular auxin homeostasis in Populus.

The LBD11-ROS feedback regulatory loop modulates vascular cambium proliferation and secondary growth in Arabidopsis

Vascular cambium produces the phloem and xylem,vascular tissues that transport resources and provide mechanical support,making it an ideal target for crop improvement.However,much remains unknown about how vascular cambium proliferates.In this study,through pharmaceutical and genetic manipulation of reactive oxygen species(ROS)maxima,we demonstrate a direct link between levels of ROS and activity of LATERAL ORGAN BOUNDARIES DOMAIN 11(LBD11)in maintaining vascular cambium activity.LBD11 activates the transcriptionof several keyROS metabolic genes,including PEROXIDASE71and RESPIRATORY BURST OXIDASE HOMOLOGS D and F,to generate local ROS maxima in cambium,which in turn enhance the proliferation of cambial cells.In a negative feedback mechanism,higher Ros levels then repress LBD11 expression and maintain the balance of cambial cell proliferation.Our findings thus reveal the role of a novel LBD11/ROS-dependent feedback regulatory system in maintaining vascular cambiumspecific redox homeostasis and radial growth inplants.

The plant vascular systemⅠ:From resource allocation,inter-organ communication and defense,to evolution of the monocot cambium

In recent years, considerable attention has been paid to exploring the complex gene regulatory networks involved in the development of the plant vascular system. Such information is crucial to our understanding of the molecular and cellular events which give rise to the integrated tissues of the xylem and phloem, leading to the formation of structurally continuous conduits that interconnect various organs of the plant. Vascular development begins in the embryo to form progenitor cells, and upon germination, these progenitor cells and their decedents in the shoot and root meristems will form phloem and xylem, and the cambium.

The plant vascular system Ⅱ:From resource allocation,inter-organ communication and defense,to evolution of the monocot cambium

In this Special Issue, a focus is placed on the role of the xylem as an essential conduit for the long-distance delivery of water and mineral nutrients from the soil to the vegetative （above-ground） regions of the plant. Xylem cells destined to form tracheids or vessel members, which will make up the conduit for this water and mineral transport from the roots to the shoots, undergo apoptosis, a process of programmed cell death.

橡胶树形成层组织的酵母双杂交cDNA文库构建及HbHDA6互作蛋白筛选

次生乳管是天然橡胶合成和贮存的场所,是由橡胶树树干树皮中维管形成层细胞分裂分化而来。次生乳管的数量与天然橡胶产量直接相关,而这些乳管的数量取决于形成层分化次生乳管的频率(乳管分化能力),是橡胶树产量育种的主要指标。前期研究中,我们发现组蛋白去乙酰化酶(HDA)抑制剂曲古抑菌素A(TSA)能诱导橡胶树乳管分化且组蛋白去乙酰化酶基因(HbHDA6)能够参与橡胶树乳管分化调控。由于组蛋白乙酰化修饰调控橡胶树次生乳管分化的分子机制尚未阐明,因此该文使用冠菌素(COR)诱导橡胶树形成层分化产生次生乳管的实验系统,以分离形成层组织为材料,构建酵母双杂交cDNA文库,以HbHDA6基因为诱饵来筛选酵母双杂交文库,确定与HbHDA6相互作用的蛋白。结果表明:(1)利用Gateway技术构建的均一化COR诱导橡胶树形成层组织的酵母双杂交cDNA文库,初级文库的容量为6.34×10^(6)CFU·mL^(-1),总单克隆数为1.27×10^(7),文库重组率为100%;次级文库的容量为7.72×10^(6)CFU·mL^(-1),总单克隆数为1.54×10^(7),文库重组率为100%。初级文库和次级文库的插入片段平均长度分别为1.1 kb和1.2 kb。(2)成功构建了筛选HbHDA6互作蛋白的pGBKT7-HbHDA6诱饵载体,并确认无自激活活性。(3)使用该诱饵载体对构建的酵母双杂交cDNA文库进行筛选,并通过NCBI_BLAST比对和去除重复以后,获得了22个与HbHDA6发生互作的蛋白,包括CLP1、ERF3、ERF4、HSP82、LARP6a、APT5、PP2A、FBA6等。该研究成果为解析组蛋白乙酰化修饰调控橡胶树次生乳管分化的分子机制提供了理论基础,为转基因改良橡胶树的产胶潜力提供了候选基因,为高性能天然橡胶遗传改良育种提供了新线索。

冠菌素诱导橡胶树次生乳管分化的形成层细胞CUT&Tag文库构建和初步分析

CUT&Tag技术是一种研究蛋白质-DNA互作的新方法,使用超高活性的新型pG-Tn5转座酶,在抗体引导下精准靶向切割目的蛋白附近的DNA序列,从而进行cDNA建库和测序分析。此技术在人类和动物研究中应用广泛,由于植物细胞结构特殊,该技术在植物研究中应用较少。在前期研究中,我们发现组蛋白乙酰化修饰参与茉莉酸诱导橡胶树次生乳管分化的调控,但其分子机制尚未阐明。本研究利用冠菌素(COR)诱导橡胶树萌条维管形成层分化次生乳管的实验系统,通过酶解法获取高质量的形成层区细胞原生质体,使用组蛋白H3乙酰化修饰抗体对次生乳管分化过程中发生组蛋白乙酰化修饰的区域进行原位识别,采用CUT&Tag技术成功构建COR处理橡胶树树皮形成层细胞的cDNA文库。对构建cDNA文库进行质检和测序分析,发现文库质量较好,并通过差异基因的GO和KEGG富集分析,发现生长素、类黄酮代谢和蛋白质泛素化等相关基因得到富集。本研究结果为使用CUT&Tag技术构建植物组织的cDNA文库提供操作方法,为解析组蛋白乙酰化修饰调控橡胶树次生乳管分化的分子机制提供理论基础。

年轮异常结构研究进展

树轮中记载了大量气候或环境信息,如何更好地从多个尺度上挖掘出树木年轮所包含的其他环境信息,是当前急需解决的重要科学问题之一。树轮是树木形成层细胞进行有规律的生长和变化而形成的。在恶劣的环境条件下或环境发生改变时,会影响形成层的正常活动,从而在树轮结构中留下一些特殊痕迹,如霜轮、伪轮、浅轮以及缺轮等异常结构的产生。而异常结构的形成与温度、降水、光照等气候因子密切相关,此外反应木及树脂道的产生主要受机械外力的作用。通过探究异常轮与环境因子的关系,有利于深入认识极端事件对树木形成层活动的影响。基于异常轮的相关报道,总结了不同类型异常结构发生的区域、涉及树种、季节条件等特征、形成机理及其在极端事件中的应用,有助于了解极端事件对森林带来的影响以及在生理角度,树木对极端事件的响应机制。以期为今后的相关研究提供新的策略方法。

油桐枝条嫁接繁育研究

【目的】由于油桐无性繁殖技术体系不成熟,目前主要靠播种实生育苗,导致油桐不能保持母本的优良性状。研究不同因素对油桐枝接成活及生长的影响,探究最适合油桐枝接的嫁接组合,为完善油桐无性繁殖技术体系提供参考,对于油桐产业提质增效和健康发展具有一定的理论和实践意义。【方法】以‘华桐1号’家系当年生半木质化带芽茎段为接穗,以千年桐优良单株家系实生苗为砧木,探究嫁接时间、嫁接方法和接穗类型对油桐枝接成活及生长的影响,待嫁接苗萌发后调查其成活率、外形生长指标、嫁接口愈合情况及最佳解膜方法。【结果】最佳的嫁接时期是夏至,最高成活率为91.67%,分别比立春、立秋和冬至最高成活率高10%、10%和4.77%,差异不显著(P>0.05),分别比春分、立夏、秋分和立冬最高成活率高25.71%、388.91%、25.71%和25.01%,差异显著(P<0.05);夏至时期成活率最高的嫁接方法是劈接法,成活率为87.50%,比切接法高9.09%,差异不显著(P>0.05),比合接法高33.32%,差异显著(P<0.05);在春分、立夏、夏至和立秋4个时期最佳的接穗类型为腋芽,分别比同时期嫁接顶芽的成活率高118.51%、100%、15.38%和19.33%,差异显著(P<0.05);在立春、秋分、立冬和冬至4个时期最佳的接穗类型为顶芽,分别比同时期嫁接腋芽的成活率高940.63%、113.61%、899.74%和323.85%,差异显著(P<0.05)。最佳解膜方式为在砧木侧轻划开嫁接膜。8个时期的嫁接苗在萌发60 d后嫁接口均已基本愈合。【结论】适宜油桐枝接的最佳季节是夏至,接穗类型为腋芽,虽然成活率最高的嫁接方法是劈接法,但综合考虑嫁接成本和嫁接效率适宜的嫁接方法为切接法,切接操作简单,每人每天可以嫁接800株以上,为油桐良种无性化育苗提供了切实可行的途径。

木本植物形成层活动的分子调控机制

维管形成层位于木质部和韧皮部之间,负责诸多生长和发育过程,在木材生产上也起重要作用。开展木本植物形成层活动的内部分子机制研究,对木本植物径向生长和林木生物量的增加具有重要的理论价值。深度成像结合基因表达分析技术是一种前沿研究方向,数学建模和仿真结合实时成像在模拟形成层生长和潜在的分子过程中有重要应用前景。基于该技术,总结了当前形成层活动分子层面的部分代表性成果,并对未来研究提出展望。目前植物形成层活动的分子研究主要集中在:(1)形成层活动受到植物激素信号的调控;(2)转录因子、肽受体信号调控形成层活动;(3)形成层活动受到受体激酶信号的调控。主要结论为:WOX4、WOX14、HB4、HB7、HB8、ANT等正向调控树木形成层活动,可作为木材增粗育种转基因的首选。未来通过计算机模型剖析形成层内细胞间通信联系,能够更全面地解析木本植物维管形成层发育分子机制。

GRP1.8融合反义4CL1基因调控烟草木质素生物合成

该研究成功地将从刺槐 (Robiniapseudoacacia)中克隆得到的定位于形成层表达的GRP1 8启动子 ,分别与GUS报告基因及从毛白杨 (Populustomentosa)中克隆的香豆酸连接酶 (4CL1)基因连接构建成GRP1 8 GUS和GRP1 8 anti 4CL1融合基因 ,转基因于烟草植物 .经组织化学检测分析 ,GUS基因成功地由GRP1 8启动子驱动定位于形成层表达 ;融合基因GRP1 8 anti 4CL1的表达明显地改变了转基因烟草植株的木质素和纤维素的含量和比例 .转基因烟草的木质素含量较对照平均降低了 13 7% ,而转基因植株的纤维素含量较对照升高了 15 6 % .

气候变化对树木木质部生长影响的研究进展

【目的】树木生长受多种气候因子的影响,与年轮宽度相比,树木木质部细胞的生长变化记录了更为详尽的气候信息,可以丰富当前从传统树轮气候学或树轮生态学研究中所得到的认识。本研究以期为利用树轮木质部细胞特征研究全球变化提供参考。【方法】综述了树木木质部形成过程、研究木质部细胞生长变化对气候因子响应的常用方法以及气候变化(温度、降水、光照强度、光周期和CO2浓度等)对形成层活动及木质部细胞生长变化的影响。【结果】目前,在细胞水平上研究树木木质部生长变化对气候因子响应过程的主要方法为:钉针法和微芯取样法,钉针法主要适用于研究形成层对损伤的响应或是记录热带树木木质部生长的增量,而微芯取样法可以清楚地观察到生长季各阶段形成层细胞数量的变化及木质部形成过程;树木木质部的生长过程一般从形成层恢复活动开始,经过细胞的伸展、次生细胞壁的加厚和木质化后,形成成熟的次生木质部细胞,其中的每一个阶段都会受到气候因子变化的影响;树木木质部细胞生长的变化与温度、降水、光照强度、光周期和CO2浓度等气候因子有着复杂的相关关系;温度主要影响树木生长季前期形成层的活动,改变形成层恢复活动的时间、细胞的分裂速率及活动周期,但并不会改变木质部细胞分化的序列和季节生长模式;降水主要影响形成层细胞分裂的速率、在生长季的持续时间以及管胞的直径等,降水不足会降低树木细胞分裂的速率,缩短细胞分化的时间,导致生长季的持续时间减少,同时抑制细胞伸展,管腔直径较小;光照强度主要影响树木的光合速率来间接影响形成层细胞的活动;光周期主要控制木质部细胞的最大生长速率和生长结束期;有关CO2浓度升高对树木木质部细胞的影响,研究结果并不一致,一些研究认为,CO2浓度升高影响细胞的分裂速率和细胞的扩张而不是次生细胞壁的加厚,从而造成早材生长轮宽度明显增加,但也有研究表明,CO2浓度升高并没有引起早材细胞结构较大的变化,相反晚材生长环的宽度却明显增加。【结论】随着研究理论和技术手段的不断成熟,极端灾害下树木木质部细胞的生长特征、不同树种木质部细胞的生长对气候变化的响应以及多种气候因子对树木木质部生长的综合影响将成为今后研究的主要方向。

毛白杨枝条木质部细胞分化的动态变化及其与形成层活动的相互关系

应用定量解剖学和显微图像分析技术 ,得到了毛白杨枝条形成层细胞与其衍生木质部细胞解剖特征在形成层活动期内的变化情况 ,并探讨了两者之间的关系。采用X射线微密度测定技术 ,了解了同一生长轮内木材密度沿径向方向上的变异 ,讨论了其与木质部细胞解剖特征之间的关系。结果表明 ,形成层纺锤形细胞的径向和弦向宽度在活动期不同阶段差异不显著 ,而纤维长度、纤维宽度、壁腔比、微纤丝角、导管分布频率和胞壁率差异极显著 ;导管组织比量差异显著 ;导管分子长度、纤维比量和射线比量差异不显著。同一生长轮内木材密度的径向变异与活动期不同阶段形成的木质部细胞数量及其解剖特征直接相关。形成层带细胞层数与纤维长度、纤维长宽比和壁腔比呈极显著负相关 ,与纤维宽度呈显著正相关 ;形成层纺锤形细胞的径向宽度与纤维长度、纤维长宽比和射线比量呈显著负相关 ;形成层纺锤形细胞的弦向宽度与纤维宽度呈显著正相关。总体看来 ,在整个形成层活动期 ,形成层纺锤形细胞与木纤维的解剖特征之间随时间变化的相关性较好 。

单人工上苗式半自动蔬菜嫁接机关键机构设计与试验

半自动嫁接机价格低、适用蔬菜种类广,但其生产能力相对低。为简化操作、提高嫁接效率,设计一种单人工补给砧木和接穗苗的贴接式半自动蔬菜嫁接机。嫁接机关键部件包括砧穗木夹持旋转机构、旋转持苗防回转机构、切削机构等;其中,旋转持苗防回转机构采用了双棘轮反向止动,实现单电机驱动双轴间歇反向旋转,保证上苗和夹持工序有序配合;确定了砧穗木上苗位、夹持、切削、嫁接工位的较优布局,可实现单人工同时上砧、穗木苗。对南瓜和丝瓜穴盘苗进行嫁接试验表明:嫁接成功率达到89%,与人工相近;嫁接效率达到846.3株/h,是人工嫁接效率的3.3倍,证明该单人工上苗操作的贴接式嫁接机满足工厂化嫁接作业要求。

毛白杨形成层的活动周期及其POD同工酶的变化

北京地区生长的毛白杨 (PopulustomentosaCarr .)在春季芽膨大前 ,形成层带已经进入了恢复活动期。在芽展开后一周形成层进入活动期 ,细胞开始分裂 ,细胞层数也有所增加 ,同时分化出未成熟的韧皮部细胞。未成熟韧皮部细胞的数量在形成层活动初期快速增长 ,随后是一个持续而缓慢的连续过程。木质部的产生比韧皮部要晚 3周 ,未成熟的木质部细胞层数在开始变化不大 ,5月底～ 6月底 ,增长速度明显高于初期 ,随后便急剧下降。成熟木质部细胞的出现比成熟的韧皮部细胞要晚约一个月。与其他研究结果不同 ,毛白杨在4月底到 6月底这段时间 ,形成层细胞层数迅速下降 ,未成熟韧皮部细胞也略有减少 ,而未成熟和成熟的木质部细胞则大量增加。木质部在 9月底停止分化 ,较韧皮部要晚约 2 0d。 9月底形成层进入休眠期后 ,形成层细胞层数基本保持不变 ,直到翌年春天恢复活动。毛白杨形成层区域的过氧化物酶 (POD)同工酶在形成层活动期其活性低、酶带少 ,而恢复活动期和休眠期其活性高且酶带多 ,组织化学反应还表明 ,不同时期POD在不同的细胞和组织中的活性不同。本文对POD同工酶在形成层活动周期中的变化与其组织分化的关系进行了讨论。