Visualization of flax cell wall lignification using a novel click chemistry analogue of sinapyl alcohol

Abstract

Lignin is a crucial component of plant cell walls, supporting plant growth by providing mechanical strength, aiding water transport, and enhancing resistance to pathogens. Despite extensive research on lignin biosynthesis as a renewable resource, understanding the transport and deposition of its monomers remains challenging. In this study, a novel precursor monomer was designed, S_ALK (alkyne-tagged sinapyl alcohol surrogate), for tracking and localizing lignin in flax cells, aiming to explore the in vivo lignification process. First, the dehydrogenation polymer (DHP) of S_ALK was synthesized and its biocompatibility was successfully verified. After click chemistry to label fluorescent dyes, incorporation of novel lignin monomers during the polymerization process was detected and imaged successfully. The results indicated that the chemical reporter could provide detailed localization information during polymerization. It was found that lignification in the bast fiber (R) cells and fiber tracheid (FT) cells of flax was different. FT cells closer to the pith showed higher maturity and lower lignification degree. While R cells, regardless of their proximity to the pith, show a relatively consistent lignification trend. At the single-cell level, lignin deposition initiates at cell corners and the middle lamella, followed by secondary cell wall, with the highest lignin content in the secondary wall of mature cells. The results of this work reveal the potential of chemical reporters in providing detailed insights into the in vivo lignification process, advancing the technology for studying the formation and function of plant cell walls.