Polysaccharide from discarded tobacco leaves and its anti-TMV activities

Natural polysaccharides have been attracted increasing attention in biopesticides for the antiviral effects. Tobacco leaves enriched the polysaccharides and had the potential against tobacco mosaic virus (TMV), however, the chemical structure and anti-TMV effect of polysaccharides from discarded tobacco leaves (DTCP) are still unclear. In this study, an optimized condition for extraction time of 3.5 h, temperature of 90 °C, and solid-liquid ratio of 1:45 led to the maximum extraction value of 21.11 % for DTCP. Subsequently, a homogeneous polysaccharide (DTP) of 3061 Da was purified from DTCP by DEAE and Sephadex G-100 column. The major monosaccharide composition of DTP was glucose (Glc), glucuronic acid (GlcA), galactose (Gal), and galacturonic acid (GalA) in a molar ratio of 3.9:2.6:1.06:0.84. NMR, methylation and IR analysis showed that DTP was a polysaccharide with →4)-β-D-Galp-(1 → 4)-β-D-Galp-(1 → 4)-β-D-Glcp as the main chain, and its branching points were composed of α-D-Glcp-(1→, α-D-GlcpA-(1→ and α-D-GalpA-(1→. Furthermore, DTP exhibited significant inactive and protective effects against TMV with the inhibitory rates of 80.40 % and 76.18 % at 500 μg/mL, respectively. DTP also interfered with the polymerization of TMV-CP to limit its self-assembly. Additionally, DTP could increase the superoxide dismutase, catalase, peroxidase and phenylalanine ammonia lyase activities of tobacco plants by 1.83, 2.73, 3.69 and 4.84 times, respectively, and could alleviate the hypersensitive response and systemic acquired resistance. Hence, DTP could serve as a new plant-derived pesticide for controlling TMV in agriculture.