Molecular Structure and Function of Protective Plant Polymers

高等植物的叶片和果实角质层主要起屏障作用，控制细菌和真菌的侵袭以及外部环境中水分和化学物质的扩散。它们的主要化学成分是提供防水的蜡和两种不溶性结构支撑聚合物中的一种，角质（用于空中器官）和木质素（用于内部位置和伤口组织）。该项目旨在了解生物聚合物的单体单元如何共价连接在一起并与细胞壁多糖相连，角质层表面的机械特性如何响应应力条件而变化，以及甜菜素或相关材料如何参与马铃薯组织的纹理硬化。我们将采用几种生物物理学的方法来解决这些问题。(1)采用化学和酶促的方法制备青柠果角质和马铃薯伤皮的低聚片段，进行色谱分离，并通过核磁共振（NMR）和质谱（MS）进行鉴定。(2)溶剂膨胀样品的核磁共振实验将用于开发和应用方法，以识别石灰果角质、马铃薯伤口表皮、浸渍绿棉和硬化马铃薯组织中的聚合物链结构、交联和细胞壁连接。(3)使用流变学、原子力显微镜（AFM）和固态核磁共振（NMR）来评估磨损、冷害和农药叶面递送对表皮力学性能和分子柔韧性的影响。(4)利用结构分析和核磁共振波谱技术研究沉积在具有“难煮综合征”的马铃薯块茎中的硬聚合物物质的生物合成。该项目的总体目标包括了解保护性角质层和亚木质素生物聚合物的单体单元如何连接在一起并支持细胞壁基质，风磨损和温度冲击等环境压力如何改变角质层膜的机械性能，水果角质层如何与农业化学品应用中使用的水性洗涤剂相互作用，以及木素或相关多酚是如何在硬化过程中合成的，从而降低了马铃薯的质地。最终，这项研究应该对农业和经济都有影响，有助于设计基本的作物保护战略。更广泛地说，从这项工作中获得的微观结构和分子见解可能有助于工业或化妆品用途的合成防水材料的开发。最后，该项目将有助于向植物科学家社区介绍固态核磁共振和原子力显微镜等方法。

The leaf and fruit cuticles of higher plants function principally as barriers, controlling bacterial and fungal attack as well as the diffusion of water and chemicals from the outside environment. Their major chemical constituents are waxes that provide waterproofing and either of two insoluble structural support polymers, cutin (for aerial organs) and suberin (at internal locations and in wound tissue). This project aims to understand how the monomer units of the biopolymers are covalently linked together and to cell-wall polysaccharides, how the mechanical properties of the cuticular surface change in response to stress conditions, and how suberin or related materials are involved in textural hardening of potato tissues. Several biophysical approaches will be taken to these problems. (1) Oligomeric fragments of lime fruit cutin and suberized potato wound periderm will be produced by chemical and enzymatic means, separated chromatographically, and identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS). (2) NMR experiments on solvent-swelled samples will be used to develop and apply methodologies to identify polymer chain structures, cross-links, and cell-wall linkages in lime fruit cutin, potato wound periderm, suberized green cotton, and hardened potato tissues. (3) The impact of abrasion, chilling injury, and foliar delivery of pesticides on cuticular mechanical properties and molecular flexibility will be assessed using rheometry, atomic force microscopy (AFM), and solid-state NMR. (4) The biosynthesis of hard polymeric substances deposited in potato tubers that have 'hard-to-cook syndrome' will be studied using texture analysis and NMR spectroscopy. The overall objectives of this project include understanding how the monomer units of the protective cutin and suberin biopolymers are linked together and to supporting cell-wall matrices, how environmental stresses such as wind abrasion and temperature shock alter the mechanical properties of the cuticular membrane, how fruit cuticles interact with aqueous detergents used in application of agrochemicals, and how suberin or related polyphenols are synthesized during the hardening process that degrades potato texture. Ultimately, this research should have both agricultural and economic impact, aiding in the design of essential crop protection strategies. More broadly, the microstructural and molecular insights developed from this work may assist the development of synthetic waterproofing materials for industrial or cosmetic use. Finally, this project will serve to introduce methods such as solid-state NMR and AFM to the community of plant scientists.