Role of suberin, suberan, and hemicellulose in phenanthrene sorption by root tissue fractions of switchgrass (Panicum virgatum) seedlings.

Sorption of organic pollutants by root tissue fractions, and the role of root turnover in mobilizing organic pollutants in soils, may help elucidate mechanisms of pollutant uptake by plants. The sorption of phenanthrene by bulk root tissue of switchgrass (Panicum virgatum) seedlings exhibits uptake much higher than predicted based on the extractable lipids in root tissues and the octanol-water partition coefficient for phenanthrene. Surprisingly, the removal of waxes, extracted by organic solvents, results in only a slight reduction in sorption, however, the subsequent removal of suberin (polymeric lipids) by saponification greatly reduces the affinity of the residual materials (by 7-fold), suggesting that suberin serves as the major sorption medium for organic pollutants. The sorption capability of suberan (i.e., lignin and cellulose) components is completely masked by coexisting hemicellulose materials. The removal of the hemicellulose by acid hydrolysis markedly enhanced the affinity of plant root tissue fractions for phenanthrene (5-40 times), which was attributed to sorption by the aromatic condensed domains as derived from solid-state 13C NMR data. Reversible sorption-desorption of bulk root tissue and the extractable lipids was observed, but the hydrolyzing fractions and the dewaxed-saponifiable residues demonstrated irreversible sorption.