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Investigation of Plant Cell Wall Properties: A Study of Contributions from the Nanoscale to the Macroscale Impacting Cell Wall Recalcitrance

机译：植物细胞壁特性的研究：研究从纳米尺度到宏观影响细胞壁顽固性的贡献。

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摘要

Biochemical conversion of lignocellulosic biomass to fuel ethanol is one of a few challenging, yet opportune technologies that can reduce the consumption of petroleum-derived transportation fuels, while providing parallel reductions in greenhouse gas emissions. Biomass recalcitrance, or resistance to deconstruction, is a major technical challenge that limits effective conversion of biomass to fermentable sugars, often requiring a costly thermochemical pretreatment step to improve biomass deconstruction. Biomass recalcitrance is imparted largely by the secondary cell wall, a complex polymeric matrix of cell wall polysaccharides and aromatic heteropolymers, that provides structural stability to cells and enables plant upright growth. Polymers within the cell wall can vary both compositionally and structurally depending upon plant species and anatomical fraction, and have varied responses to thermochemical pretreatments. Cell wall properties impacting recalcitrance are still not well understood, and as a result, the goal of this dissertation is to investigate structural features of the cell wall contributing to recalcitrance (1) in diverse anatomical fractions of a single species, (2) in response to diverse pretreatments, and (3) resulting from genetic modification.;In the first study, feedstock cell wall heterogeneity was investigated in anatomical (stem, leaf sheaths, and leaf blades) and internode fractions of switchgrass at varying tissue maturities. Lignin content was observed as the key contributor to recalcitrance in maturing stem tissues only, with non-cellulosic substituted glucuronoarabinoxylans and pectic polysaccharides contributing to cell wall recalcitrance in leaf sheath and leaf blades. Hydroxycinnamate (i.e., saponifiable p-coumarate and ferulate) content along with xylan and pectin extractability decreased with tissue maturity, suggesting lignification is only one component imparting maturity specific cell wall recalcitrance.;In the second study, alkaline hydrogen peroxide and liquid hot water pretreatments were shown to alter structural properties impacting nanoscale porosity in corn stover. Delignification by alkaline hydrogen peroxide pretreatment decreased cell wall rigidity, with subsequent cell wall swelling resulting in increased nanoscale porosity and improved enzymatic hydrolysis compared to limited swelling and increased accessible surface areas observed in liquid hot water pretreated biomass. The volume accessible to a 90 A dextran probe within the cell wall was found to be positively correlated to both enzyme binding and glucose hydrolysis yields, indicating cell wall porosity is a key contributor to effective hydrolysis yields.;In the third study, the effect of altered xylan content and structure was investigated in irregular xylem (irx) Arabidopsis thaliana mutants to understand the role xylan plays in secondary cell wall development and organization. Higher xylan extractability and lower cellulose crystallinity observed in irx9 and irx15 irx15-L mutants compared to wild type indicated altered xylan integration into the secondary cell wall. Nanoscale cell wall organization observed using multiple microscopy techniques was impacted to some extent in all irx mutants, with disorganized cellulose microfibril layers in sclerenchyma secondary cell walls likely resulting from irregular xylan structure and content. Irregular secondary cell wall microfibril layers showed heterogeneous nanomechanical properties compared to wild type, which translated to mechanical deficiencies observed in stem tensile tests. These results suggest nanoscale defects in cell wall strength can correspond to macroscale phenotypes.
机译：木质纤维素生物质的生化转化为燃料乙醇是极富挑战性的技术之一，可以减少石油衍生的运输燃料的消耗，同时减少温室气体的排放。生物质的顽固性或抗解构性是一项重大技术挑战，它限制了将生物质有效转化为可发酵糖的能力，这通常需要昂贵的热化学预处理步骤来改善生物质的解构。生物质的顽固性主要是由次级细胞壁赋予的，次级细胞壁是细胞壁多糖和芳香族杂聚物的复杂聚合物基质，可为细胞提供结构稳定性，并使植物直立生长。细胞壁内的聚合物可以根据植物种类和解剖部分而在组成和结构上变化，并且对热化学预处理具有不同的响应。细胞壁特性对顽固性的影响尚不十分清楚，因此，本论文的目的是研究导致顽固性的细胞壁的结构特征（1）在单个物种的不同解剖部位中，（2）作为响应（3）基因改造产生的结果。在第一项研究中，研究了不同组织成熟度的柳枝node的解剖学（茎，叶鞘和叶片）和节间级分的原料细胞壁异质性。仅在成熟的干组织中观察到木质素含量是导致顽固性的关键因素，非纤维素取代的葡萄糖醛酸阿拉伯糖基木聚糖和果胶多糖有助于叶片鞘和叶片中细胞壁的顽固性。随着组织的成熟，羟基肉桂酸酯（即皂化的对香豆酸盐和阿魏酸酯）含量，木聚糖和果胶的可提取性降低，表明木质素化只是赋予成熟特定细胞壁顽抗性的一种成分；在第二项研究中，碱性过氧化氢和液态热水预处理结果表明，改变玉米秸秆中纳米级孔隙率的结构特性。与在液体热水预处理的生物质中观察到的有限溶胀和增加的可及表面积相比，通过碱性过氧化氢预处理进行的脱木素作用降低了细胞壁的刚度，随后的细胞壁溶胀导致纳米级孔隙率增加和酶水解改善。发现细胞壁内90 A葡聚糖探针可及的体积与酶结合和葡萄糖水解产量均呈正相关，表明细胞壁孔隙率是有效水解产量的关键因素。研究了不规则木质部（irx）拟南芥突变体中木聚糖含量和结构的变化，以了解木聚糖在次级细胞壁发育和组织中的作用。与野生型相比，在irx9和irx15 irx15-L突变体中观察到较高的木聚糖可萃取性和较低的纤维素结晶度，表明木聚糖整合入次生细胞壁中。使用多种显微镜技术观察到的纳米级细胞壁组织在所有irx突变体中都受到了一定程度的影响，硬化的次生细胞壁中纤维素微原纤维层的组织紊乱可能是由于不规则的木聚糖结构和含量所致。与野生型相比，不规则的次生细胞壁微纤维层显示出异质的纳米机械性能，这转化为茎拉伸试验中观察到的机械缺陷。这些结果表明细胞壁强度的纳米级缺陷可以对应于宏观表型。

著录项

  • 作者

    Crowe, Jacob Dillon.;

  • 作者单位

    Michigan State University.;

  • 授予单位 Michigan State University.;
  • 学科 Chemical engineering.;Plant sciences.;Materials science.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 214 p.
  • 总页数 214
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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