Degree Name

Master of Science (MS)

Semester of Degree Completion

1985

Thesis Director

Roger Darding

Abstract

The compositions and sugar linkages of the acidic extracellular polysaccharide (EPS) from several Rhizobium trifolii mutants were compared. These mutants were derived from a wild type Rhizobium trifolii, ANU843, and are unable to cause normal root hair curling, Hac-, or nodulate clover, Nod-. Three of the mutants contain a Tn5 insertion in a 5.3 kb BglII fragment of the symbiotic plasmid (pSym). A fourth mutant is missing the pSym, which includes much of the 5.3 kb BglII fragment, both of these deletions result in Hac-Nod- phenotypes. When the 5.3 kb BglII fragment is cloned (pRT150) and reinserted into the pSym- mutant extreme root hair curling occurs (hac++), but the strain still does not nodulate, Nod-. If a self-transmissible pSym (pBR1AN) from another Rhizobium trifolii is introduced into the pSym- mutant both root hair curling and nodulation responses are restored. These results suggest that the EPSs of these strains are identical in structure. Comparison with known EPS structures from other Rhizobium trifolii, Rhizobium phaseoli and Rhizobium leguminosarum strains suggest that they are the same as reported. These results suggest that neither the genes on the 5.3 kb BglII fragment of the pSym nor those on the entire pSym are involved in the biosynthesis of the overall EPS structure. In addition, correction of Hac- phenotype with pRT150 and of the Hac-Nod- phenotype with pBR1AN does not alter the EPS structure. Thus these results also suggest that the acidic EPS are not involved in the early event of marked root hair curling. These conclusions must be qualified somewhat since the locations of base labile substituents, acetate and B-hydroxybutyrate, have not been determined.

Download

Share

COinS