The Forming Of Transfer Cells Induced By Rhizobia In Root Of Some Legume Species And The Primary Study On Its Mechanism

This study has investigated the legumes of Albizia julibrissin; Astragalus simicus; Medicago sativa; Trifolium pratense; Robinia pseudoacacia; Caragana sinica; Pisum sativum; Glycine max to verify if it is a common phenomenon that rhizobia can induce the forming of transfer cells on the legume's root surface. After certain time of culture of the aseptic seedlings inoculated with Rhizobia, the root segments which had distinctive deformation of root hairs were selected to fix for prepare of specimens, meanwhile, the seedlings without Rhizobia are set and treated as the control. The semi-thin section and ultrathin section of prepared specimen were separately observed through optical microscope and transmission electron microscope. The result indicated that the rhizobia can induce the forming of transfer cells in all these plants, however, with different positions in different plants. The transfer cells of Albizia julibrissin distribute in the epidermis and exodermis. Those of Astragalus sinicus in epidermis and root hairs, those of Medicago sativa in epidermis or in the exodermis or in the epidermis exodermis and the cortex cells next the exodermis,Those of Triforlium pratense in the epidermis or in the exodermis or in the epidermis and exodermis at the same time, those of Robinia pseudoacacia in the epidermis exodermis and root hairs, those of Caragana sinicu in the exodermis.those of Pisum sativum and Glycine max in the epidermis.Except for the transfer cells, the rhizobia can also induce the lateral roots of Albizia julibrissin and Robinia pseudoacacia to produce more root hairs. There are more deformed root hairs on the lateral root's base part of inoculated Albizia julibrissin's seedlings than on the control. There are many longer and denser root hairs on the lateral roots of the Robinia pseudoacacia inoculated with rhizobia than on the controlThe microchemiscal study on the lateral root's segments of Robinia pseudoacacia shows that there are more Fe3+ exist in the root segment of inoculated seedlings than in the contral, as maybe explained the hypothesis that the transfer cells will increase the absorption of the Fe3+After the aseptic seedlings of Astragalus sinicus and Robinia pseudoacacia were treated by nod factors, they all can be resulted in root hairs deformation. But we did not oberserved their root segments swell or the empty nodules form. The observation of semi-thin section of root segments with distinctive root hair diformation show that transfer cells formed on the root surface of Astragalus sinicus while not on the surface of the Robinia pseudoacacia. This suggests that the forming of the transfer cells of Astragalus sinicus was induced by rhizobia because of the nod factors.We find that there are many tranafer cells of the Glycine max around vessel elements in the metaxylem of the main root, which can explain the phenomenon of vessel's active transport.