ABSTRACT
The p lan t’s prim ary, or “grow ing,” cell wall is thought to comprise a high tensile strength netw ork o f cellulose m icrofibrils tethered by cross-linking glycans and em bedded in an independent bu t interactive pectin m atrix o f uronic acid-rich polysaccharides [1,2]. The pectin m atrix has several struc tural and physiological roles in plants, and am ong the pectic polysaccha rides are some o f the m ore complex polymers found in the plant cell wall. Pectins establish dom ains o f fixed anionic environm ents w ithin the wall, creating a weakly acidic extracellular milieu th a t is the m ajor cationexchange m atrix o f the plant. The pectins also establish the “pore size” o f the wall by generating anionic channels o f about 4 nm in diam eter [3]. There is evidence for the presence o f a large proportion o f galactose in some cell walls [4] and a recent nuclear m agnetic resonance (NM R) study [5] suggests th a t this neutral galactan may be further involved in lim iting porosity by form ing short flexible rods anchored at one end th a t pro trude into the pores o f the netw ork.
