Despite lignin being a key component of wood, the dynamics of tracheid lignification are generally overlooked in xylogenesis studies, which hampers our understanding of environmental drivers and blurs the interpretation of isotopic and anatomical signals stored in tree rings. Here, we analyzed cell wall formation in silver fir (Abies alba Mill.) tracheids to determine if cell wall lignification lags behind secondary wall deposition. For this purpose, we applied a multimodal imaging approach combining transmitted light microscopy (TLM), confocal laser scanning microscopy (CLSM), and confocal Raman microspectroscopy (RMS) on anatomical sections of wood microcores collected in northeast France on 11 dates during the 2010 growing season. Wood autofluorescence after laser excitation at 405 nm and 488 nm associated with the RMS scattering of lignin and cellulose, respectively, which allowed identification of lignifying cells (cells showing lignified and non-lignified wall fractions at the same time) in CLSM images. The number of lignifying cells in CLSM images mirrored the number of wall-thickening birefringent cells in polarized TLM images, revealing highly synchronized kinetics for wall thickening and lignification (similar timings and durations at the cell level). CLSM images and RMS chemical maps revealed a substantial incorporation of lignin into the wall at early stages of secondary wall deposition. Our results show that most of the cellulose and lignin contained in the cell wall undergo concurrent periods of deposition. This suggests a strong synchronization between cellulose and lignin-related features in conifer tree-ring records, as they originated over highly overlapped time frames.

中文翻译：

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银杉的多模态成像分析揭示了纤维素和木质素沉积的协调性

尽管木质素是木材的关键成分，但在木质发生研究中，管胞木质化的动态通常被忽视，这阻碍了我们对环境驱动因素的理解，并模糊了对树木年轮中存储的同位素和解剖信号的解释。在这里，我们分析了银杉（Abies alba Mill.）管胞的细胞壁形成，以确定细胞壁木质化是否滞后于次生壁沉积。为此，我们对 2010 年生长期间 11 个日期在法国东北部收集的木材微芯的解剖切片应用了结合透射光显微镜 (TLM)、共焦激光扫描显微镜 (CLSM) 和共焦拉曼显微光谱 (RMS) 的多模态成像方法。季节。 405 nm 和 488 nm 激光激发后的木材自发荧光分别与木质素和纤维素的 RMS 散射相关，这允许在 CLSM 图像中识别木质化细胞（同时显示木质化和非木质化壁部分的细胞）。 CLSM 图像中的木质化细胞数量反映了偏振 TLM 图像中壁增厚双折射细胞的数量，揭示了壁增厚和木质化高度同步的动力学（细胞水平上相似的时间和持续时间）。 CLSM 图像和 RMS 化学图显示，在次生壁沉积的早期阶段，木质素大量掺入壁中。我们的结果表明，细胞壁中含有的大部分纤维素和木质素经历同时的沉积期。这表明针叶树年轮记录中纤维素和木质素相关特征之间存在很强的同步性，因为它们起源于高度重叠的时间范围。