Abstract
Summary Seven of the main enzymes involved in nitrogen metabolism were studied in the organs of a scrophulariaceae holoparasite Lathraea clandestina L. With only one exception (nitrite reductase) all these enzymatic activities were found to be highest in the scale leaves. Nitrate reductase, nitrite reductase, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities were shown markedly lower than in C 3 (tobacco) and C 4 (maize) leaves. The glutamate oxoglutarate aminotransferase (GOT) capacity of Lathraea is close to that of C 3 and C 4 , whereas urease and glutamate dehydrogenase (GDH) capacities were several times higher. The Krebs-Henseleit cycle and a high urease capacity could provide ammonia for GDH activity. Large and synchronous changes of GDH, GOT, and phosphoenolpyruvate carboxylase (PEPc) capacities were observed during a day period. So, it seems that in the case of Lathraea , a parasite of alder, nitrogen assimilation takes place mainly through GDH activity provided in ammonia by desamination of metabolites, mainly citrulline, transferred from the host, and also through transamination from glutamic acid as suggested by the high GOT activity.
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