CHEMICAL-COMPOSITION OF PARENCHYMA AND SCLERENCHYMA CELL-WALLS ISOLATED FROM ORCHARDGRASS AND SWITCHGRASS

The isolation and analysis of cell-wall types (CWT) such as parenchyma and sclerenchyma provide a means of understanding the complex chemistry of forage fiber. Our objective was to compare the composition of parenchyma and sclerenchyma cell walls of field-grown orchardgrass (Dactylis glomerata L.) and switchgrass (Panicum virgatum L.) harvested at four stages of plant maturity. Leaf blades, leaf sheaths, and stems were analyzed for fiber constituents. Parenchyma and sclerenchyma cell walls were mechanically isolated from plant parts and analyzed for neutral sugars, alkali-labile phenolic acids, and lignin. Neutral-detergent fiber (NDF), hemicellulose, cellulose, and lignin concentrations differed (P < 0.05) between plant parts. Parenchyma cell walls differed widely in composition, with arabinose ranging from 25 to 81 g kg-1; xylose, 92 to 282 g kg-1; glucose, 410 to 634 g kg-1; p-coumaric acid, 1 to 19 g kg-1; ferulic acid, 2 to 10 g kg-1; and lignin, 38 to 104 g kg-1. Sclerenchyma cell walls were more uniform in composition, with arabinose ranging from 10 to 30 g kg-1; xylose, 204 to 330 g kg-1; glucose, 411 to 533 g kg-1; p-coumaric acid, 5 to 16 g kg-1; ferulic acid, 3 to 9 g kg-1; and lignin, 51 to 99 g kg-1. In most cases, the ratios of xylose to arabinose and p-coumaric acid to ferulic acid were lower (P < 0.05) in parenchyma compared with sclerenchyma, and in leaf blade or leaf sheath CWT compared with those of the stem. These results suggest that the chemistry of CWT is complex and that studies of heterogenous preparations such as NDF are confounded by the chemical diversity of CWT contained in forages.