The Specific Nature of Plant Cell Wall Polysaccharides

Abstract

Summa111I(-r1Y. Polysaccharide compositions of cell walls were assessed by quantitative anialyses of the component sugars. Cell walls were hydrolyzed in 2 N trifluoroacetic acid and the liberated stugars reduced to their respective aldiltols. The alditols were acetylated and the resulting alditol acetates separated by gas chromatography. Quan-ti,tative assay o,f the alditol acetates was accomplished by electronically integrating the detector outputt of the gas chromatograph. Iyo-inositol, introduced into the sample pri,or to hydrolysis, served as anl internal standard. The cell wall polysaccharide compositions of plant varieties within a given species are essenti,ally identical. However, differences in the stugar composition were ob-served in cell walls prepared from different species of the same as well as o,f different genera. The fact that the wNal,l com,positi,ons of different varieties of the same species are the same indicates that the biosynthesis of cell wall polysaccharides is genetically regullated. The cell wal,l,s of various morphological parts (roots, hypocotyls, first internodes and primary le,aves) of bean plants were each found to have a characteristic sugar composition. It was found that the cel,l wall stugar composition of suspension-cultured sycamore cells could be altered by growing the cells on different carbon sources. This demon-strates that the biosynthesis of cell wall polysaccharides can be manipulated without fatal consequences. The cell walls of higher plants are complex orgainelles which are composed primarily of poly-saccharide aInd protein (14). In addition, the presence of smaller amoounts of lipid (18) aind ribonutcleic acid (12, 17) constituents has been re-ported, andl a intumber of enzymies have beeni foulnd to be localize,d within the cell wall (16). The structulral complexity anid anato,mical distinctiveness of dlifferent cell walls are well known from light anid, more recently, electroni microscope stuidies (1,5,9,22). The structtural complexity of the cell wall anid the pre,sence there of various metabolically importaint components suiggest that the wall imiay have other functions in addition to its established role of providing mechanical support for the cell. Polysacchariles are the major constituents of cell walls. T,he macromole,cules involved are com-posed of both ineuitral sugars and uironiic acids (2). The compositions of cell wall polysaccharides differ somewhat in walls prepare,d from plaints belonigiing to (lifferent families (6, 20). Furthermore, the compo-sition of wvalls aippears to have a role in celltular growth, for it has been demonstrated that the polysaccharide composition chainges duiriing de-velopment (20). Changes in the cell wall poly-saccharide oomposition have also been correlated with indoleacetic acid-induced eloingationi of oat coleoptiles (19). However, the degree to which the cell has control over cell wall polysaccharide synithesis aind the degree of absolute consitancy of the polysaccharide comipositi,on of higher plant cel' walls remain to be established. If the cell walls were randomly synthesized, small chaniges in poly-saccharide composition might have no significance, as these changes c0ould not be correlated with such wall rellated phentometna as growth. I,f the com-position1 of the wall were precise, however, small chan1ges in compositilon coutld be of great importance. One aspect of otur work has beeni concerned with host-pathogen initerrelationships. In geineral, plant pathogens are able to prodtuce enzymies capable of breakinIg down polysacchari,des. 1)ifferences be-tween resistant and susceptilble plaints may involve, at least in part, the ability of the wall polysac-charides to resist enzymatic degradation. In order