Composition of cell walls isolated from cell types of grain sorghum stems

Cell types were isolated from sorghum stems at two stages of development, a nthesis and grain maturity, to study cell wall characteristics. Cell walls were isolated from epidermis (EPID), sclerenchyma (SCL), vascular bundle zo ne (VBZ), inner vascular bundles (IVB) and pith parenchyma cells (PITH) and analysed for total carbohydrate, acid insoluble lignin, total uronosyls, n eutral sugars and hydroxycinnamic acids. In addition, walls from SCL, VBZ, IVB and PITH were subjected to chemical fractionation to separate wall carb ohydrate into polysaccharide groups. Although wall characteristics were sim ilar at both plant maturities, there were differences in lignin concentrati on, hydroxycinnamic acids, and carbohydrate composition among the cell wall types. Lignin was lowest in the PITH walls (169 g kg(-1)) and highest in S CL and EPID (c 211 g kg(-1)). Cellulose was most abundant in VBZ and SCL wa lls with greater secondary wall formation. Pectic materials were most abund ant in PITH walls. Xylans were similar among wall types except for EPID tha t contained higher amounts of xylose. Releasable hydroxycinnamates were not as consistent among the cell wall types. Total ferulates, including ester linked and releasable ether linked, tended to increase from PITH to SCL (g to 15 g kg(-1) CW) with an increase in the proportion etherified within the wall matrices (PITH 51%; SCL 66%). Total p-coumarates showed opposite tren ds with PITH walls having significantly more (35 g kg(-1) CW) than VBZ or S CL (19 and 13 g kg(-1) CW). EPID walls contained the least pCA (6.5 g kg(-1 ) CW). Except for the hydroxycinnamates, compositional trends for the diffe rent wall. types would reflect changes from primary walls to increased amou nts of secondary wall. Neutral sugar analysis of indigestible residues indi cated similar carbohydrate compositions among the cell wall types, with xyl ose being less degradable than all other wall sugars. (C) 1999 Society of C hemical Industry.