Structural Variation and Polysaccharide Profiling of Intervessel Pit Membranes

Functional roles of intervessel pit membrane (PM) depend on its structure and polysaccharide composition, which are mostly unknown or lack of accurate information. This study uses grapevine as a model plant and an immunogold-scanning electron microscopy technique to simultaneously analyze structures and polysaccharide compositions of intervessel PMs in relation to their functions. Intervessel PMs with different structural integrity were found in functional xylem with about 90 % of them being intact with a smooth or relatively smooth surface and the rest 10 % with progressively degraded structures. The results also elucidated details of the removal process of wall materials from surface toward its depth during the natural intervessel PM degradation. Four groups of pectic and hemicellulosic polysaccharides were present in intervessel PMs but displayed differential spatial distributions and quantities: weakly methyl-esterified homogalacturonans abundant in the surficial layers, heavily methyl-esterified homogalacturonans and xylans mostly in deep layers, and fucosylated xyloglucans relatively uniform in presence at different depths of an intervessel PM. This information is crucial to reveal the polysaccharide profiling of primary cell wall and to understand intervessel PMs roles in the safety and regulation of water transport as well as the plant susceptibility to vascular diseases.