Structural variation and spatial polysaccharide profiling of intervessel pit membranes in grapevine

Abstract Background and Aims Intervessel pit membranes (PMs) are important cell wall structures in the vessel system that may impact a plant’s water transport and its susceptibility to vascular diseases. Functional roles of intervessel PMs largely depend on their structure and polysaccharide composition, which are the targets of this study. Methods With grapevine used as a model plant, this study applied an immunogold-scanning electron microscopy technique to simultaneously analyze intervessel PM structures and major pectic and hemicellulosic polysaccharides that compose intervessel PMs at high resolution. Key Results Intervessel PMs in functional xylem showed significant structural variation with about 90 % of them being structurally intact with smooth or relatively smooth surfaces and the remaining 10 % with progressively degraded structures. The results also elucidated details of the removal process of cell wall materials from intervessel PM surface toward its depth during its natural degradation. Four groups of pectic and hemicellulosic polysaccharides were immunolocalized in intervessel PM and differed in their spatial distribution and abundance. Weakly methyl-esterified homogalacturonans (WMe-HGs, detected by JIM5) was abundant in the surface layer, heavily methyl-esterified homogalacturonans (HMe-HGs, detected by JIM7) and xylans detected by CCRC-M140 were mostly found in deeper layers, and fucosylated xyloglucans (F-XyGs, detected by CCRC-M1) were more uniformly distributed at different depths of the intervessel PM. Conclusions Intervessel PMs displayed diverse structural variations in grapevine. They contained certain major groups of pectic and hemicellulosic polysaccharides with different spatial distributions and abundance. This information is crucial to reveal the polysaccharide profiling of the primary cell wall and to understand intervessel PM’s roles in the regulation of water transport as well as in a plant’s susceptibility to vascular diseases.