Quantification and monosaccharide composition of hemicelluloses from different plant functional types

Hemicelluloses are the second most abundant polysaccharide in nature after cellulose. So far, thechemical heterogeneity of cell-wall hemicelluloses and the relatively large sample-volume required inexisting methods represent major obstacles for large-scale, cross-species analyses of this important plant compound. Here, we apply a new micro-extraction method to analyse hemicelluloses and the ratioof &lsquo;cellulose and lignin&rsquo; to hemicelluloses in different tissues of 28 plant species comprising fourplant functional types (broad-leaved trees, conifers, grasses and herbs). For this study, the fiber analysisafter Van Soest was modified to enable the simultaneous quantitative and qualitative measurements ofhemicelluloses in small sample volumes. Total hemicellulose concentrations differed markedly amongfunctional types and tissues with highest concentration in sapwood of broad-leaved trees (31% d.m.in Fraxinus excelsior) and lowest concentration between 10 and 15% d.m. in leaves and bark of woodyspecies as well as in roots of herbs. As for total hemicellulose concentrations, plant functional types and tissues exhibited characteristic ratios between the sum of cellulose plus lignin and hemicelluloses, with very high ratios (<4) in bark of trees and low ratios (>2) in all investigated leaves. Additional HPLC analyses of hydrolysed hemicelluloses showed xylose to be the dominant hemicellulose monosaccharide in tissues of broad-leaved trees, grasses and herbs while coniferous species showed higher amounts of arabinose, galactose and mannose. Overall, the micro-extraction method permitted for the simultaneous determination of hemicelluloses of various tissues and plant functional types which exhibited characteristic hemicellulose concentrations and monosaccharide patterns.