CARBON AND NITROGEN-METABOLISM IN A HOLOPARASITIC PLANT, LATHRAEA-CLANDESTINA L, WITH RESPECT TO THE MAIN PHENOLOGIC STAGES

Several aspects of carbon and nitrogen metabolism were studied in a Scrophulariaceae holoparasite, Lathraea clandestina L., with respect to the main phenologic stages. A good interrelation between sucrose and malate contents, and phosphoenol pyruvate carboxylase and glutamate oxoglutarate amino transferase activities was demonstrated. Concerning nitrogen metabolism two main points should be underlined. Firstly, nitrate reduction was shown to be incomplete and very low. Secondly, ammonium assimilation takes place mainly through the glutamine synthetase and glutamate synthase pathways, although glutamate dehydrogenase activity is several times higher than in autotrophic plants and should be taken into consideration, particularly during the spring phenologic stages when the flowering shoots begin to degenerate and the ammonia concentration increases. Great changes in enzyme capacities were observed in Lathraea tissues according to the time of measurement during a 24 h cycle, whereas no daily changes were observed over the period of 1 week. Significant changes were demonstrated from one phenologic stage to another, especially between pre- and postflowering stages. PEPc and GOT activities were twice as low in spring because carbohydrate and malate concentrations decreased markedly. Among nitrogen metabolism enzymes, GDH exhibited the largest variations and was evidenced at a high level during spring stages, i.e. 3 - 5 times higher than during preflowering periods. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.