Multidimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy has emerged as an indispensable technique for resolving polymer structure and intermolecular packing in primary and secondary plant cell walls. Isotope (13C) enrichment provides feasible sensitivity for measuring 2D/3D correlation spectra, but this time-consuming procedure and its associated expenses have restricted the application of ssNMR in lignocellulose analysis. Here, we present a method that relies on the sensitivity-enhancing technique Dynamic Nuclear Polarization (DNP) to eliminate the need for 13C-labeling. With a 26-fold sensitivity enhancement, a series of 2D 13C–13C correlation spectra were successfully collected using the unlabeled stems of wild-type Oryza sativa (rice). The atomic resolution allows us to observe a large number of intramolecular cross peaks for fully revealing the polymorphic structure of cellulose and xylan. NMR relaxation and dipolar order parameters further suggest a sophisticated change of molecular motions in a ctl1 ctl2 double mutant: both cellulose and xylan have become more dynamic on the nanosecond and microsecond timescale, but the motional amplitudes are uniformly small for both polysaccharides. By skipping isotopic labeling, the DNP strategy demonstrated here is universally extendable to all lignocellulose materials. This time-efficient method has landed the technical foundation for understanding polysaccharide structure and cell wall assembly in a large variety of plant tissues and species.

中文翻译：

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未标记植物细胞壁的固态核磁共振：无需同位素富集的高分辨率结构分析


多维固态核磁共振（ssNMR）光谱已成为解析初级和次级植物细胞壁中聚合物结构和分子间堆积的不可或缺的技术。同位素 (13C) 富集为测量 2D/3D 相关光谱提供了可行的灵敏度，但这种耗时的过程及其相关费用限制了 ssNMR 在木质纤维素分析中的应用。在这里，我们提出了一种依赖于动态核极化 (DNP) 灵敏度增强技术来消除 13C 标记的需要的方法。使用野生型稻（水稻）的未标记茎，成功收集了一系列 2D 13C–13C 相关光谱，灵敏度提高了 26 倍。原子分辨率使我们能够观察到大量的分子内交叉峰，从而充分揭示纤维素和木聚糖的多晶型结构。 NMR 弛豫和偶极序参数进一步表明 ctl1 ctl2 双突变体中分子运动的复杂变化：纤维素和木聚糖在纳秒和微秒时间尺度上变得更加动态，但两种多糖的运动幅度一致较小。通过跳过同位素标记，此处演示的 DNP 策略可普遍扩展到所有木质纤维素材料。这种省时的方法为了解多种植物组织和物种中的多糖结构和细胞壁组装奠定了技术基础。