Relationship between bacteroid poly-beta-hydroxybutyrate accumulation and nodule functioning in the Galega orientalis-Rhizobium galegae symbiosis under diamine treatment.
Exposure of Galega orientalis plants to diamines putrescine (Put) and cadaverine (Cad) at concentrations from 0.01 to 2.0 mM significantly altered carbon and nitrogen metabolism in their root nodules. Correlative studies of bacteroid poly-beta-hydroxybutyrate (PHB) content and acetylene-reduction capacity of the nodules revealed a negative relationship between these parameters. Utilisation of PHB deposits by bacteroids and high acetylene reduction activity was observed when applying low diamine concentrations. The increase in PHB accumulation in response to high diamine levels was accompanied by a considerable decline in nodule nitrogenase activity. Supplying isolated Galega bacteroids with various diamine concentrations significantly modified bacteroid oxygen consumption, which might be associated with alterations in carbon flux to the bacteroids. Finally, modulation of the bacteroid content upon Put and Cad treatment was examined. The results are discussed in terms of possible causes of the diamine-induced changes in nodule metabolism.