Cytochemical Localization of Polysaccharides in Dendrobium officinale and the Involvement of DoCSLA6 in the Synthesis of Mannan Polysaccharides

Abstract

<i>Dendrobium officinale</i> is a precious traditional Chinese medicinal plant because of its abundant polysaccharides found in stems. We determined the composition of water-soluble polysaccharides and starch content in <i>D</i>. <i>officinale</i> stems. The extracted water-soluble polysaccharide content was as high as 35% (w/w). Analysis of the composition of monosaccharides showed that the water-soluble polysaccharides were dominated by mannose, to a lesser extent glucose, and a small amount of galactose, in a molar ratio of 223:48:1. Although starch was also found, its content was less than 10%. This result indicated that the major polysaccharides in <i>D</i>. <i>officinale</i> stems were non-starch polysaccharides, which might be mannan polysaccharides. The polysaccharides formed granules and were stored in plastids similar to starch grains, were localized in <i>D</i>. <i>officinale</i> stems by semi-thin and ultrathin sections. <i>CELLULOSE SYNTHASE-LIKE A</i> (<i>CSLA</i>) family members encode mannan synthases that catalyze the formation of mannan polysaccharides. To determine whether the <i>CSLA</i> gene from <i>D</i>. <i>officinale</i> was responsible for the synthesis of mannan polysaccharides, <i>35S</i>:<i>DoCSLA6</i> transgenic lines were generated and characterized. Our results suggest that the <i>CSLA</i> family genes from <i>D. officinale</i> play an important role in the biosynthesis of mannan polysaccharides.