EFFECTS OF AGE, DARKNESS AND NITRATE ON POLY-BETA-HYDROXYBUTYRATE LEVELS AND NITROGEN-FIXING ABILITY OF RHIZOBIUM IN LUPINUS-ANGUSTIFOLIUS

The effects of age, darkness and nitrate on nitrogenase activity, poly‐β‐hydroxybutyrate (PHB) and β‐hydroxybutyrate dehydrogenase (BOHB DH) activity in Rhizobium lupini while in symbiosis with Lupinus angustifolius were assessed. It was concluded that PHB functions as a reserve material in root nodules and is involved in the maintenance of nitrogen fixation when the availability of photosynthates is restricted. PHB accumulation and the development of BOHB‐DH activity did not take place until the peak of nitrogenase activity had passed. All three parameters reached a steady level when the host plant was approximately 24 days old. Deprivation of photosynthates due to continuous darkness resulted in major losses of PHB and BOHB‐DH activity until N2‐fixation ceased. Nitrate addition without restriction of photosynthates resulted in diminished nitrogenase activity. Apart from a slight delay in accumulation. PHB levels were not affected. It was found important to standardize sampling since N2‐fixation was affected by plant culture and diurnal cycles. Copyright © 1978, Wiley Blackwell. All rights reserved