S. Renaudin

Ribulose 1,5-biphosphate carboxylase activity in the holoparasite Lathraea clandestina L.

Summary A ribulose 1,5-biphosphate carboxylase (EC 4.1.1.39) activity was demonstrated and determined in the organs of the holoparasitic Scrophulariaceae Lathraea clandestina L.The determinations were performed using a crude extract purified through precipitation with 20 % to 65 % saturated ammonium sulfate. Two determination methods were used: one, spectrophotometric, based on NADH oxidation following the incorporation of CO2, the other, radioisotopic, measuring incorporated radioactivity after contact with NaH14CO3.RuBP carboxylase activity was found to be highest in the scale leaves; yet, it is 10 to 20 times lower than in C3-type leaves like those of tobacco or spinach.

Carbon Nutrition in a Rafflesiaceae Holoparasite Cytinus hypocistis L. Fixed on, or Experimentally Isolated from the Host Cistus Monspeliensis L.

Abstract The host-parasite pair Cistus Monspeliensis-Cytinus hypocistis is fed, via the aerial organs of the host, with 14 CO 2 . The radioactivity measurements show that the main substances transfered from the host to the parasite are sucrose, glutamic acid, and aspartic acid. The parasite isolated from the host is also shown to be capable of fixing atmospheric 14 C thus fixed represents about 12% of the 14 C received from the host by the non-isolated parasite. The nature of the labelled products found in the detached parasite not only confirms the existence of PEP carboxylase activity, but also suggests the intervention of a RuBP carboxylase.

Trophic relations of the dwarf mistletoe Arceuthobium oxycedri with its host Juniperus oxycedrus

Summary A basipetal transfer of 14 C-labelled assimilates is demonstrated from the host needles towards the aerial shoots of the parasite that acts as sink here. However, the endophytic system (= haustorium) of the parasite accumulates almost no radioactivity. The transferred substances are essentially soluble carbohydrates and amino acids (mainly asparagine). In the experimental conditions, the amount of carbon obtained from the host by the parasite may be estimated to be approximatively equal to the amount that it can fix from atmospheric CO 2 . The comparative study of mineral elements by X-ray microanalysis shows that the endophytic tissues of the parasite are richer in S, P and chiefly K than the close neighbouring host tissues, and consequently that the [K]/[Ca] ratio is higher in the parasite. It thus seems that mineral elements as well as organic compounds can be withdrawn by the endophytic system from both xylem and phloem of the host.

Characterization of Phosphoenolpyruvate Carboxylase in a Range of Parasitic Phanerogames

Summary Presence of phosphoenolpyruvate carboxylase (PEPC) was demonstrated in the tissues of various hemiparasitic and holoparasitic plants. The specific activity of the enzyme was found to be very close to those exhibited by C3 non-parasitic plants. With regard to their immunological properties, PEPC of parasitic plants are related to PEPC of Sorghum bicolor, a C4 plant. PEPC was not characterized either in the holoparasite Cytinus hypocistis or in saprophytic higher plants. The putative roles of PEPC in parasitic plants are discussed.

Activity and immunocytochemical localization of glutamine synthetase inLathraea clandestins L.

SummaryThe activity of glutamate synthetase (GS) was determined in the different organs ofLathraea clandeslina L., a holoparasitic Scrophulariaceae. It was very low throughout the plant but levels were slightly higher in the scale leaves. Immunoprecipitation reactions carried out with immune serums raised against the isoforms GS1 or GS2 of the enzyme showed that, in the scale leaves, isoenzyme GS1 was present, but the existence of small amounts of GS2 remained in question on account of possible cross reactions. On the other hand, the study of intracellular localization of GS in the scale leaves by indirect immunofluorescence, using the same antibodies anti-GS1 and anti-GS2, clearly demonstrated the occurrence of two GS forms: a GS1 isoenzyme located in the cytoplasm of glandular and parenchymatous cells and a GS2-type isoenzyme only detected in the stroma of the large amyloplasts present in the outer parenchyma. This amyloplastidial isoenzyme seems to be a peculiar GS form, distinct from both GS1 and GS2.

The Incorporation of 14CO2 in the Organic Substances of the Holoparasitic Scrophulariaceae Lathraea clandestina L. Separated from its Host.

Summary Shoots of Lathraea clandestina , a holoparasitic plant, were isolated from their host-plant and placed in an atmosphere enriched in 14 CO 2 . Subsequent analysis of the plant tissues demonstrated that the parasite is able to assimilate some atmospheric CO 2 . A comparison with a previous study of the transfer of organic substances from the host-plant (alder) to Lathraea shows that this incorporation of external CO 2 by the parasitic plant is not quantitatively important in its total carbon nutrition but that it gives rise to metabolites different in their nature and their proportions from those coming from the host. The main labelled compounds were found to be organic acids and free amino acids. This is to be related to a PEP carboxylase activity. Otherwise, the presence of labelled fructose and glucose suggests that a Ru BP carboxylase activity could also occur.

Phosphoenol Pyruvate Carboxylase in Parasitic Plants: Further Characterization in Various Species and Localization at the Level of Cells and Tissues in Lathraea clandestina L.

Phosphoenolpyruvate carboxylase (PEP carboxylase, EC 4.1.1.31) activity was demonstrated in a range of holo and hemiparasitic phanerogams. Lathraea clandestina was used as a model for a more detailed study. Enzyme activity levels were determined in the various plant parts. Great changes in enzyme capacity were observed in the shoots according to the time of measurement during a 24 hr cycle. PEP carboxylase characterized at the cellular level by using an indirect immunofluorescence method was found to be mainly located in the cytosol. The possible functions of PEP carboxylase in parasitic plants are discussed.

Nitrogen metabolism key enzyme activities in a scrophulariaceae holoparasite Lathraea clandestina L.

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.

Carbon and Nitrogen Metabolism in a Holoparasitic Plant, Lathraea clandestina L., with Respect to the Main Phenologic Stages

Summary 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.