A comparative transcriptomic study and a single-cell metabolome analysis were combined to determine whether parenchymal ray cells contribute to the biosynthesis of monolignols in the lignifying xylem of Norway spruce (Picea abies). Ray parenchymal cells may function in the lignification of upright tracheids by supplying monolignols. To test this hypothesis, parenchymal ray cells and upright tracheids were dissected with laser-capture microdissection from tangential cryosections of developing xylem of spruce trees. The transcriptome analysis revealed that among the genes involved in processes typical for vascular tissues, genes encoding cell wall biogenesis-related enzymes were highly expressed in both developing tracheids and ray cells. Interestingly, most of the shikimate and monolignol biosynthesis pathway-related genes were equally expressed in both cell types. Nonetheless, 1,073 differentially expressed genes were detected between developing ray cells and tracheids, among which a set of genes expressed only in ray cells was identified. In situ single cell metabolomics of semi-intact plants by picoliter pressure probe-electrospray ionization-mass spectrometry detected monolignols and their glycoconjugates in both cell types, indicating that the biosynthetic route for monolignols is active in both upright tracheids and parenchymal ray cells. The data strongly support the hypothesis that in developing xylem, ray cells produce monolignols that contribute to lignification of tracheid cell walls.

中文翻译：

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射线薄壁细胞有助于挪威云杉木质部发育中管胞的木质化。

比较转录组学研究和单细胞代谢组分析相结合，以确定实质射线细胞是否有助于挪威云杉（云杉）木质部木质素单体的生物合成。射线实质细胞可以通过提供木质素单体在直立管胞的木质化中起作用。为了检验这一假设，用激光捕获显微切割技术从云杉树发育中木质部的切向冷冻切片中解剖了实质射线细胞和直立管胞。转录组分析显示，在参与维管组织典型过程的基因中，编码细胞壁生物发生相关酶的基因在发育中的管胞和射线细胞中均高度表达。有趣的是，大多数莽草酸和木质素单体生物合成途径相关基因在两种细胞类型中的表达相同。尽管如此，在发育中的射线细胞和管胞之间检测到1,073个差异表达基因，其中鉴定了一组仅在射线细胞中表达的基因。通过皮升压力探针-电喷雾电离-质谱法对半完整植物进行原位单细胞代谢组学，在两种细胞类型中检测到木质素单体及其糖缀合物，表明木质素单体的生物合成途径在直立管胞和实质射线细胞中都很活跃。这些数据有力地支持了这样的假设：在木质部发育过程中，射线细胞产生有助于管胞细胞壁木质化的木质素单体。