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首页> 外文学位 >Structure and function of endosperm starch from maize mutants deficient in one or more starch-branching enzyme isoform activities.
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Structure and function of endosperm starch from maize mutants deficient in one or more starch-branching enzyme isoform activities.

机译：缺乏一种或多种淀粉分支酶同工型活性的玉米突变体的胚乳淀粉的结构和功能。

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摘要

The goal of this thesis is to understand the effects of deficiency of maize starch-branching enzyme (SBE) isoform activities on endosperm starch molecular and granular structure and starch digestion, with emphasis on the effect of SBEI deficiency. A preliminary test of endosperm starch digestibility for the sbe1a mutant showed that deficiency of SBEI caused a decreased susceptibility of starch granules to pancreatic alpha-amylase. This was the first indication of an effect of deficiency of SBEI alone in synthesis of endosperm starch and justified further investigation of the function of SBEI isoform. Consequently, this thesis describes the study of the structure and function of sbe1a mutant endosperm starch compared to non-mutant (wild-type, Wt) starch.;Chain length profile was examined for the non-granular starch and starch fractions from Wt and sbe1a, as well as for the RS from Wt and sbe1a. Although chain length profiles of native starch molecules appeared very similar for Wt and sbe1a, some small differences between the two genotypes were observed in the chain length profile of their RS, as well as in the comparison of the chain length profile of their RS to native starch. Compared to Wt, fewer amylose-like chains were digested in RS from sbe1a. Iodine binding analysis of starch fractions showed that sbe1a samples had higher lambdamax than Wt samples.;The amylose fraction from Wt and sbe1a starch was subjected to exhaustive beta-amylolysis. sbe1a starch had more long residual chains, suggesting that the distribution of branch points on these long amylose chains may be closer to the non-reducing ends. Debranching of beta-limit dextrin from amylose by isoamylase was less complete in sbe1a, suggesting that closely associated branch points may be more prevalent in amylose from sbe1a.;Granule structure for native starches and residual granule structure for the respective RS were examined by microscopy. Scanning and transmission electron micrographs show that the RS from sbe1a mutant retained more of the granule integrity. A resistant peripheral layer by microscopy observed for the sbe1a RS may help understand the decreased digestibility of sbe1a starch. Sbe1a is more strongly expressed in the later stage of endosperm development (Gao et al. 1996). Thus, if most of the later-synthesized starch is deposited in the peripheral region of the growing granule, starch synthesized in the sbe1a mutant would be expected to be affected predominantly in the peripheral region.;Starch utilization and coleoptile growth of Wt and sbe1a mutant kernels were measured during kernel germination. After Day 6 germinating sbe1a kernels exhibited a slower rate of coleoptile growth and an accordingly decreased rate of starch hydrolysis as compared to Wt kernels, suggesting compromised starch utilization in germinating sbe1a kernels.;The evidence obtained in this thesis, coupled with previous research, leads to several hypotheses about the specific functions of the three maize SBE isoforms in endosperm starch biosynthesis: (1) The SBEIIb protein is the dominant form of SBE, and is responsible for synthesizing branch points that are clustered. (2) When SBEIIb is present, SBEI is responsible for modulating the branching pattern by synthesizing branch points that are less locally clustered, and SBEIIa is responsible for modulating the branching pattern by synthesizing branch points that are more locally clustered. (3) When SBEIIb is absent, SBEI and SBEIIa may have a reciprocal inhibitory function on synthesis of branch points.;This thesis also for the first time reports that a lack of SBEI activity resulted in an observable effect, which was seen on both starch molecular structure and starch function. Structural and functional analysis of endosperm starch deficient in SBEI activity strongly supports the hypothesis that SBEI is required to synthesize starch granules for normal kernel development, allowing efficient hydrolysis and utilization. Evidence from this thesis reveals a unique and essential function of SBEI in normal plant development, consistent with the evolutionary conservation of SBEI in all higher plants. (Abstract shortened by UMI.)
机译：本文的目的是了解玉米淀粉分支酶（SBE）同工型缺乏对胚乳淀粉分子和颗粒结构以及淀粉消化的影响，重点是SBEI缺乏的影响。 sbe1a突变体的胚乳淀粉消化率的初步测试表明，SBEI的缺乏导致淀粉颗粒对胰腺α-淀粉酶的敏感性降低。这是在胚乳淀粉合成中单独使用SBEI缺乏效果的第一个迹象，并且有必要进一步研究SBEI亚型的功能。因此，本论文描述了与非突变型（野生型，Wt）淀粉相比，sbe1a突变型胚乳淀粉的结构和功能的研究。检验了链长分布图，分析了非颗粒淀粉以及来自Wt和sbe1a的淀粉级分，以及来自Wt和sbe1a的RS。尽管天然淀粉分子的链长图谱对于Wt和sbe1a看起来非常相似，但是在它们的RS链长图谱以及它们的RS与天然淀粉的链长图谱的比较中，观察到了两种基因型之间的一些小差异。淀粉。与Wt相比，RS从sbe1a中消化的直链淀粉样链更少。淀粉级分的碘结合分析表明sbe1a样品的lambdamax比Wt样品高。Wt和sbe1a淀粉的直链淀粉级分经过详尽的β-淀粉分解。 sbe1a淀粉具有更长的残留链，这表明这些长直链淀粉链上分支点的分布可能更靠近非还原末端。 β-极限糊精通过异淀粉酶从直链淀粉上的脱支在sbe1a中不太完全，这表明在sbe1a的直链淀粉中紧密相关的分支点可能更普遍。;通过显微镜检查了天然淀粉的颗粒结构和相应RS的残留颗粒结构。扫描和透射电子显微镜照片显示，来自sbe1a突变体的RS保留了更多的颗粒完整性。通过显微镜观察到的sbe1a RS的抗性外围层可能有助于了解sbe1a淀粉的消化率降低。 Sbe1a在胚乳发育的后期更加强烈地表达（Gao等，1996）。因此，如果大多数后来合成的淀粉沉积在生长颗粒的外围区域中，则预期在sbe1a突变体中合成的淀粉将主要在外围区域受到影响。Wt和sbe1a突变体的淀粉利用率和胚芽鞘生长在籽粒发芽期间测量籽粒。第6天发芽的sbe1a籽粒与Wt籽粒相比，胚芽鞘生长速度较慢，淀粉水解速率相应降低，表明在发芽的sbe1a籽粒中淀粉利用受到损害。关于三种玉米SBE亚型在胚乳淀粉生物合成中的特定功能的一些假设：（1）SBEIIb蛋白是SBE的主要形式，负责合成簇状的分支点。 （2）当存在SBEIIb时，SBEI负责通过合成局部聚类较少的分支点来调制分支模式，而SBEIIa负责通过合成局部聚类较多的分支点来调制分支模式。 （3）当不存在SBEIIb时，SBEI和SBEIIa可能对分支点的合成具有相反的抑制作用;;本论文也首次报道缺乏SBEI活性导致可观察到的作用，这在两种淀粉上均可见分子结构和淀粉功能。缺乏SBEI活性的胚乳淀粉的结构和功能分析有力地支持了SBEI合成淀粉颗粒以进行正常籽粒发育，允许有效水解和利用的假设。该论文的证据揭示了SBEI在正常植物发育中的独特且必不可少的功能，这与SBEI在所有高等植物中的进化保守性一致。 （摘要由UMI缩短。）

著录项

  • 作者

    Xia, Huan.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Agriculture Food Science and Technology.;Agriculture Plant Culture.;Health Sciences Nutrition.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 260 p.
  • 总页数 260
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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