Metabolism of poly-\-hydroxybutyric acid in bacteroids ofRhizobium lupini in connection with nitrogen fixation and photosynthesis

Summary The darkening of lupin plants grown in a sand culture on a nitrogen-free medium at a stage of initial flowering led to a sharply decreased nitrogen fixation intensity which eventually ceased. Decreased intensity of nitrogen fixation in bacteroids was accompanied by an accumulation of poly--hydroxybutyric acid (PHB); in the course of 10–20 h (depending upon temperature) its content increased by 2.5–3.0 times. If, following darkening, the plants were once again exposed to light, an abrupt increase of nitrogen fixation intensity was observed and a simultaneous decrease of PHB content.It has been shown that lupin's exposure to light in¹⁴CO₂ atmosphere lasting 19 h resulted in the latter's incorporation into PHB, bacteroids and into the entire nodule; these processes developed almost in parallel.During the early period of vegetation growth prior to flowering, the PHB content of bacteroids decreased from 13–14 to 3–4% of dry weight, whereas the intensity of nitrogen fixation was raised. Concurrently increase of the activity of some enzymes connected with the PHB metabolism (acetoacetyl-CoA-reductase, acetyl-CoA-acetyl transferase, PHB-depolymerase, CoA-transferase of 3-ketoacids) occured. The plants' subsequent ageing and reduction of nitrogen fixation intensity led to a noticeable increase of PHB content and a decrease of the above mentioned enzymes' activity. The specific activity of \-hydroxybutyric dehydrogenase involved with PHB catabolism was high and was maintained at a constant level throughout the entire vegetative period.