Carbon and Nitrogen Metabolism in Plant-Derived Ineffective Nodules of Pea (Pisum sativum L.)

Organogenesis of legume root nodules and the construction of the nitrogen fixation system require exchanges of molecular signals between rhizobia and the host plant to activate the expression of all the necessary genes. Plant mutants with ineffective nodules are potentially useful for studies of the host-plant control and regulation of symbiotic nitrogen fixation. In this paper the nodules of three different Nod+ Fix- pea mutants (Sym 13, Sym 31 and FN1) as well as their parent lines (Sparkle, Sprint 2 and Rondo) formed on plants by the same rhizobial strain and grown in the same controlled environment cabinet, were compared for selected physiological and biochemical parameters. All mutants are monogenic, recessive and non-allelic. The Sprint 2 Fix- (Sym 31) mutant is characterized by a block in bacteroid differentiation and abnormal symbiosome structure (Borisov et al., 1993). By contrast, mutants El 35 (Sym 13) and FN1 were characterized by early senescence of the symbiosomes and nodules as a whole (Kneen et al., 1990; Postma et al., 1990).