Plant Cell Wall, a Challenge for Its Characterisation

The plant cell wall is a complex 3D network composed of polysaccharides, lignin and proteins. The knowledge of the structure and content of each cell wall polymer is a prerequisite to understand their functions during plant development and adaptation but also to optimise their industrial applications. The analysis of cell wall compounds is complicated by their multiple molecular interactions. In this review, we present numerous methods to purify, characterise and quantify proteins, polysaccharides and lignin from the wall. Two kinds of approaches are detailed: the first presents in vitro methods which involve the breakdown of the molecular linkages between polymers thanking to chemical, physical and/or enzymatic treatments. The second approach describes in situ methods that allow the cell wall polymer characterisation thanking to many analytical techniques coupled with microscopy. If microscopy is the common point of all of them, their development is associated with improvement of analytical techniques, increasing their power of resolution.

Virus-Induced Gene Silencing Offers a Functional Genomics Platform for Studying Plant Cell Wall Formation

Virus-induced gene silencing （VIGS） is a powerful genetic tool for rapid assessment of plant gene functions in the post-genomic era. Here, we successfully implemented a Tobacco Rattle Virus （TRV）-based VlGS system to study functions of genes involved in either primary or secondary cell wall formation in Nicotiana benthamiana plants. A 3-week post- VIGS time frame is sufficient to observe phenotypic alterations in the anatomical structure of stems and chemical composition of the primary and secondary cell walls. We used cell wall glycan-directed monoclonal antibodies to demonstrate that alteration of cell wall polymer synthesis during the secondary growth phase of VIGS plants has profound effects on the extractability of components from woody stem cell walls. Therefore, TRV-based VlGS together with cell wall component profiling methods provide a high-throughput gene discovery platform for studying plant cell wall formation from a bioenergy perspective.

Dietary fiber in plant cell walls-the healthy carbohydrates

Dietary fiber(DF)is one of the major classes of nutrients for humans.It is widely distributed in the edible parts of natural plants,with the cell wall being the main DF-containing structure.DF content varies significantly in different plant species and organs,and the processing procedure can have a dramatic effect on the DF composition of plant-based foods.Given the considerable nutritional value of DF,a deeper understanding of DF in food plants,including its composition and biosynthesis,is fundamental to the establishment of a daily intake reference of DF and is also critical to molecular breeding programs for modifying DF content.In the past decades,plant cell wall biology has seen dramatic progress,and such knowledge is of great potential to be translated into DF-related food science research and may provide future research directions for improving the health benefits of food crops.In this review,to spark interdisciplinary discussions between food science researchers and plant cell wall biologists,we focus on a specific category of DF--cell wall carbohydrates.We first summarize the content and composition of carbohydrate DF in various plant-based foods,and then discuss the structure and biosynthesis mechanism of each carbohydrate DF category,in particular the respective biosynthetic enzymes.Health impacts of DF are highlighted,and finally,future directions of DF research are also briefly outlined.

The plant cell wall

Research on the many aspects of the plant cell wall has experienced reiuvenation during the past few years. This is perhaps mainly due to the commercial interest in the chemical components of the cell wall that have potential for industrial use＂ Cellulose for fibers and together with hemicelluloses for bioethanol, lignin for plastics or biofuel, pectins as gel agents, let alone woody cell wall material for construction or pulp production and for intelligent materials for electronics - the new uses are mindboggling!

A brief view of international conference on plant cell wall biology 2017

The triennial International Conference on Plant Cell Wall Biology has been held 5 times since it was initiated in the United States.PCWB2017 for the first time is organized in China.The conference was attended with more than 220 participants and featured with oral and poster presentations,reflecting the contemporary status of plant cell wall studies.

Physiological Response of the Resurrection Fern Subjected to Environmental Stress as Shown by Plant Cell Membrane Integrity

Resurrection fern has a unique ability to maintain cell wall integrity when the plant cell is desiccated. It uses proteins such as late embryogenesis proteins and heat shock proteins to maintain their cellular functions. The purpose of this experiment is to determine the effects of environmental stressors on the physiological response of the resurrection fern (Pleopeltis polypodioides). The physiological response of resurrection fern plants was subjected to various temperatures (-50°C, 0°C, 25°C, and 50°C) for 7 days. Results indicated that there was a significant difference between hydrated and desiccated ferns based on the temperature. Additionally, electrolyte leakage measurements confirmed cell damage following exposure to temperature extremes of -50°C and 50°C.

<i>Azospirillum</i>Growth Promotion Is Related to Changes in Ferulate and Dehydrodiferulate Contents in Cell Wall of Inoculated Cucumber Seedlings Hypocotyls

Azospirillum brasilense is a well known plant growth-promoting rhizobacterium. Plant cell growth is constrained by the primary cell wall (CW) which contains polysaccharide-bound hydroxycinammic acids (HCAs). They derive from phenylpropanoid metabolism, which first step is the reaction catalyzed by phenylalanine ammonia-lyase (PAL;EC 4.3.1.24). Also CW peroxidases (FAPOD;EC 1.11.1.7) play a key role in the stiffening of the CW, and in the cessation of cell elongation. Knowledge of the biochemical effects the bacteria could elicit into plant CW and how these responses could change the hypocotyl physiology still remains scarce. The objective of this work was to unravel the effects of A. brasilense Sp245 inoculation on HCAs of the primary CW in apical and basal segments of cucumber seedlings hypocotyls. Azospirillum inoculation increased hypocotyls’ length. Transferulate and p-coumarate were the major HCAs. Dimmers were detected only in the basal region of 13- and 15-d-old hypocotyls. The ratio t-ferulate/dimmer (an inverse index of CW cross-linking) was five times higher in inoculated seedlings. Enzyme activities determined were not directly involved in HCAs content changes. It was previously reported that the CW was a target for A. brasilense growth promotion. This work corroborates that the phenolics, FA, DFA, and p-coumarate bound to the CW are also involved in Azospirillum plant growth promoting strategies.

拟石莲花属‘碧桃’腐烂病病原菌的鉴定及其主要致病物质的测定

采用组织分离法和单孢子纯化法,从拟石莲花属多肉植物品种‘碧桃’(Echeveria cv.‘Peach Pride’)疑似腐烂病的叶片组织获得病原菌,通过形态学和分子序列特征的鉴定以及致病性测定,明确病原菌为尖孢镰刀菌(Fusarium oxysporum)。测定尖孢镰刀菌的主要致病物质,发现该病原菌具有较强的细胞壁降解酶活性,并具有一定的产毒素(镰刀菌酸)能力,说明细胞壁降解酶类和毒素是该病原菌侵入、定殖和致病的主要因素。

Cellulose synthesis in land plants

All plant cells are surrounded by a cell wall that provides cohesion,protection,and a means of directional growth to plants.Cellulose microfibrils contribute the main biomechanical scaffold for most of these walls.The biosynthesis of cellulose,which typically is the most prominent constituent of the cell wall and therefore Earth’s most abundant biopolymer,is finely attuned to developmental and environmental cues.Our understanding of the machinery that catalyzes and regulates cellulose biosynthesis has substantially improved due to recent technological advances in,for example,structural biology and microscopy.Here,we provide a comprehensive overview of the structure,function,and regulation of the cellulose synthesis machinery and its regulatory interactors.We aim to highlight important knowledge gaps in the field,and outline emerging approaches that promise a means to close those gaps.

Elucidating the role of SlXTH5 in tomato fruit softening

Fruit softening in tomato(Solanum lycopersicum)is closely associated with cell wall disassembly,which is brought about through the action of a range of cell wall structure-related enzymes and other proteins such as expansins.Xyloglucan endotransglucosylase/hydrolase(XTH)(EC 2.4.1.207 and/or EC 3.2.1.151)has been proposed to be key player involved in xyloglucan metabolism.SlXTH5 showed the highest expression level among all SlXTHs during tomato ripening.In this study,the role of SlXTH5 involved in tomato softening was investigated in CRISPR-based knockout mutants of SlXTH5.Loss-of-function of SlXTH5 in transgenic tomato lines resulted in slightly firmer fruit pericarp,but significantly decreased their color index compared with azygous wild type(WT)control fruits.Increased paste viscosity was detected in CRISPR mutants,indicating that the activity of SlXTH5 is responsible for maintaining cell wall structural integrity.Immunocytochemistry studies were performed using the monoclonal antibody probe LM25 to examine the localization and distribution of xyloglucan in the pericarp cells of the CRISPR mutant fruits.The data indicated more xyloglucan was retained in the pericarp of CRISPR mutant fruit than in WT control fruit.This study revealed the link between SlXTH5 and xyloglucan metabolism and indicated the potential of manipulating SlXTH5 to regulate fruit softening.

Targeting and Regulation of Cell Wall Synthesis During Tip Growth in Plants

Root hairs and pollen tubes are formed through tip growth, a process requiring synthesis of new cell wall material and the precise targeting and integration of these components to a selected apical plasma membrane domain in the growing tips of these cells. Presence of a tip-focused calcium gradient, control of actin cytoskeleton dynamics, and formation and targeting of secretory vesicles are essential to tip growth. Similar to cells undergoing diffuse growth, cellulose, hemi-celluloses, and pectins are also deposited in the growing apices of tip-growing cells. However, differences in the manner in which these cell wall components are targeted and inserted in the expanding portion of tip-growing cells is reflected by the identification of elements of the plant cell wall synthesis machinery which have been shown to play unique roles in tip-growing cells. In this review, we summarize our current understanding of the tip growth process, with a particular focus on the subcellular targeting of newly synthesized cell wall components, and their roles in this form of plant cell expansion.

A general method for assaying homo-and hetero-transglycanase activities that act on plant cell-wall polysaccharides

Transglycanases（endotransglycosylases） cleave a polysaccharide（donor-substrate） in mid-chain, and then transfer a portion onto another poly-or oligosaccharide（acceptor-substrate）. Such enzymes contribute to plant cellwall assembly and/or re-structuring. We sought a general method for revealing novel homo- and hetero-transglycanases, applicable to diverse polysaccharides and oligosaccharides, separating transglycanase-generated3 Hpolysaccharides from unreacted3H-oligosaccharides—the former immobilized（on filter-paper, silica-gel or glassfiber）,the latter eluted. On filter-paper, certain polysaccharides [e.g.（1!3, 1!4）-b-D-glucans] remained satisfactorily adsorbed when water-washed; others（e.g. pectins） were partially lost. Many oligosaccharides（e.g. arabinan-, galactan-, xyloglucan-based） were successfully eluted in appropriate solvents, but others（e.g. [3H]xylohexaitol, [3H]mannohexaitol[3H]cellohexaitol） remained immobile. On silica-gel, all3 Holigosaccharides left an immobile ‘ghost’ spot（contaminating any3H-polysaccharides）, which was diminished but not prevented by additives e.g. sucrose or Triton X-100. The best stratum was glassfiber（GF）, onto which the reactionmixture was dried then washed in 75% ethanol. Washing led to minimal loss or lateral migration of3H-polysaccharides if conducted by slow percolation of acidified ethanol. The effectiveness of GF-blotting was well demonstrated for Chara vulgaris transb-mannanase. In conclusion, our novel GF-blotting technique ef ficiently frees transglycanase-generated3H-polysaccharides from unreacted3H-oligosaccharides,enabling high-throughput screening of multiple postulated transglycanase activities utilising chemically diverse donorand acceptor-substrates.

Release, Recycle, Rebuild： Cell-Wall Remodeling, Autodegradation, and Sugar Salvage for New Wall Biosynthesis during Plant Development

Plant cell walls contain elaborate polysaccharide networks and regulate plant growth, development, mechanics, cell-cell communication and adhesion, and defense. Despite conferring rigidity to support plant structures, the cell wall is a dynamic extracellular matrix that is modified, reorganized, and degraded to tightly control its properties during growth and development. Far from being a terminal carbon sink, many wall polymers can be degraded and recycled by plant cells, either via direct re-incorporation by trans- glycosylation or via internalization and metabolic salvage of wall-derived sugars to produce new precur- sors for wall synthesis. However, the physiological and metabolic contributions of wall recycling to plant growth and development are largely undefined. In this review, we discuss long-standing and recent evi- dence supporting the occurrence of cell-wall recycling in plants, make predictions regarding the develop- mental processes to which wall recycling might contribute, and identify outstanding questions and emerging experimental tools that might be used to address these questions and enhance our understanding of this poorly characterized aspect of wall dynamics and metabolism.

基于CiteSpace植物细胞壁的研究进展

运用CiteSpace软件,以Web of Science核心合集数据库为来源,时间跨度为2012—2021年,对植物细胞壁研究中满足检索条件的4794条文献进行定性定量的可视化分析.结果表明:近10年内,植物细胞壁研究的年发文量随年份增加呈上升趋势.国家之间有较多的合作,中国与其他国家的合作仅次于美国位居世界第二;中国科学院和中国农业科学院在该领域的积极性最高,在机构发文量中分别占据前2位,并拥有较多的合作关系;近10年内的不同时间段出现不同的研究热点,细胞壁完整性是最新出现的突现关键词,有望成为未来的研究热点.

纤维素、半纤维素与木质素间相互作用研究进展

纤维素、半纤维素和木质素是木质纤维生物质细胞壁中的3种主要组分,其通过复杂的相互作用形成超分子网络结构,使木质纤维生物质具有优异的机械性能及抵抗物理、化学和微生物降解的能力,同时也导致生物质预处理和组分分离困难。本文总结了近年来关于纤维素、半纤维素与木质素间相互作用的研究进展,重点介绍了木质素与半纤维素之间的共价键、范德华力和静电作用等,以期在原子-分子水平上充分认识和了解细胞壁结构,为通过基因工程合成易降解的木质纤维原料,或寻找清洁高效的生物质精炼技术提供一定的理论指导。

植物硼营养高效的分子调控途径

植物体内的硼主要存在于细胞壁中,对稳定细胞壁结构和促进生长发育起重要作用。双子叶植物需硼多,对缺硼敏感,但不同物种及不同品种对缺硼的抗性存在极显著的基因型差异。华中农业大学王运华教授在1990年代带领团队开展甘蓝型油菜硼高效品种的筛选,从此开启了我国植物硼营养高效利用的遗传与分子机制研究。近10多年的研究结果表明,植物响应缺硼胁迫提高硼效率存在2条不同的分子调控途径。(1)依赖硼转运基因的途径。在这条途径中,NIPs和BORs家族基因受缺硼诱导表达增强根系对土壤硼的吸收和体内硼的转运分配,实现硼的高效吸收和转运,进而提高植物对缺硼胁迫的抗性或适应性;(2)独立于硼转运基因的途径。该途径中,植物通过影响激素信号和细胞壁合成代谢相关基因的表达,调节根系生长发育和细胞壁组分结构等方式,提高体内硼的利用效率,进而增强植物对缺硼的抗性。在硼被确定为植物必需营养元素的百年纪念之际,我们对这一工作进行综述归纳,以飨读者。同时,在王运华先生逝世1周年之际,深切缅怀先生在开启华中农业大学作物硼营养遗传研究领域中所做的奠基性贡献。

植物细胞壁结构及成像技术研究进展

植物细胞壁作为细胞外复杂交联网络,为植物细胞生长、发育以及适应环境变化提供机械支撑,具有调节植物形态、抵抗胁迫、运输水分等功能。除此之外,植物光合作用积累的生物质大部分贮藏在细胞壁中,因此,研究细胞壁的成分和纳微结构对更好的利用植物能源具有重要意义。植物细胞壁的结构研究是当今植物界研究的前沿热点之一。随着新型成像技术的发展,近年来关于细胞壁成分和纳微结构的研究取得了阶段性的进展。本文就植物细胞壁的成分、结构、成像技术和力学性质进行了总结与展望,以期为植物细胞壁的相关研究提供新思路。

植物生长调节剂对‘无核紫’葡萄裂果特性的影响

分析不同浓度的植物生长调节剂处理‘无核紫’葡萄裂果的发生与细胞壁代谢物质及细胞凋亡之间的关系,探究造成‘无核紫’裂果特性差异的主要生理原因,找到最适宜‘无核紫’的外源植物生长调节剂喷施浓度。以易裂品种‘无核紫’果实为试验材料,花后10~15 d喷施不同浓度植物生长调节剂为处理,在成熟期采摘离体果实浸水24 h统计裂果率,通过酶联免疫分析法对果实中的水溶性果胶、原果胶、半纤维素及PG、PEP、CE、PL酶活性进行测定,采用TUNEL染色法对细胞凋亡率进行观察统计。结果表明,浸水24 h,不同处理之间存在显著差异,100 mg/L赤霉素加5 mg/L氯吡脲裂果率为56%,裂果率最低且显著低于其他处理,细胞凋亡程度较低;原果胶、半纤维素与裂果率负相关性达到极显著水平,PEP酶活性与裂果率负相关性达到显著水平;水溶性果胶/原果胶与裂果率的正相关性达到极显著水平。表明适当喷施赤霉素加氯吡脲可以提高PEP、CE酶活性,增加半纤维素、原果胶含量,降低细胞凋亡率,缓解裂果发生。

外源酶制剂在反刍动物上的应用与展望

反刍动物能够将人类不能利用的粗饲料转化为优质蛋白质——肉和奶,这对农业以及人类社会有着重要意义。但是这种转化效率与植物细胞壁的消化率有重要关系,目前植物性原料消化率较低,影响了转化效率。在反刍动物饲粮中补充外源酶制剂具有提高植物纤维消化的潜力,从而提高饲粮的利用效率。本文总结了外源酶制剂应用现状、作用模式以及发展方向,认为目前外源酶制剂在反刍动物应用上有积极的结果,也存在效果不明显的报道,这可能与酶谱、添加水平、添加方式、底物类型以及宿主的生产水平等方面有关。同时阐述了外源酶制剂是在饲喂前、瘤胃中、瘤胃后的不同环境中起到作用,但详细机制还需要继续深入探究。综上所述,尽管酶制剂应用还存在一些问题,以提高饲料消化率为目标的酶制剂仍将会是反刍动物添加剂发展的一个重要方向。