Effect Of Rhizobia Symbiosis On Lignin Levels And Forage Quality In Alfalfa(Medicago Sativa)

Rhizobia symbiosis plays important roles in the growth and development of legume plants, and lignin limits the digestibility and nutritional value of forage. However, we understand little about the relationship between rhizobia symbiosis and lignin levels in legumes. The present work investigated the effect of rhizobia symbiosis on lignin levels and forage quality in alfalfa(Medicago sativa).Alfalfa were planted in two sets, alfalfa inoculated rhizobia and alfalfa not-inoculated rhizobia. Lignin content, composition and the expression levels of several lignin biosynthetic genes were analyzed. Furthermore, alfalfa phenotypic characterization and forage quality parameters of both sets were measured to evaluate the impact of rhizobia symbiosis on forage quality in alfalfa.The results included:(1) Alfalfa inoculated rhizobia showed increased lignin content and G monomer,decreased H monomer and S/G ratio compared with alfalfa not-inoculated rhizobia(P < 0.05).We could speculate that rhizobia symbiosis affected alfalfa lignin content and composition of lignin components.(2)According to the expression of lignin biosynthetic genes in AN and NN, the expression levels of PAL in shoot and root were significantly up-regulated in AN compared with NN(P < 0.01), as were the expression levels of C4 H.CCR and CAD in root were significantly up-regulated in AN(P < 0.05). We concluded that rhizobia symbiosis could change the expression of lignin biosynthetic genes, and result in the change of composition of lignin components in alfalfa.(3)The content of ADF,NDF and Hemicellulose increased in AN, and the IVTD of dry matter values showed that NN were more digestible(P < 0.01), compared with AN.(4)According to the nutrient element content, the levels of K in AN were significantly lower than that of NN, while the expression levels of Ca in AN significantly increased compared with NN.