P. 1981. Nitrate assimilation and nitrogen circulation in Austrian pine. -Physiol. Plant. 53: 105-110.Nitrate uptake, reduction and translocation were examined in 5-week-oId Austrian pines (Pintts nigra Arnold var. nigricans Host.) during exposure to 5 mJW NaNOj. The rate of nitrate uptake was line,ar during the 7 h light period. '^N-NOJ was detected in all parts of the pine except in the needles. By the 7th hour, 43% of the absorbed nitrate had been reduced, and this increased to 64% by the 24th hour. The noajor part of the total reduction occurred in the roots at this growth stage. Accumulation of ^^N in reduced soluble and insoluble fractions was more prevalent m roots than in shoots. In the needles, the translocated nitrogen was mainly incorporated into the insoluble fraction. It is likely that most of the nitrogen from nitrate was transported from the roots to the aerial org,ans as organic nitrogen; however part of the upward nitrogen flus took place as nitrate ions. An experiment in which an exposure for 24 h to 5 mM Na"'NO3 was followed by 13 days exposure to Na^NOj (pulse chase experiment) revealed a half time of about 1 day for depletion of root nitrate. A large p,art of this depletion was due to the loss of "N-NO3 to the nutrient solution. The remaining pool of "N-nitrate was partitioned between a metabolically inactive and an active pool. During the chase period, the simultaneous decrease of ^^N-incorporation in the soluble N fraction ,and increase in the insoluble N fraction in different pine parts, particularly in the needles, suggested that protein synthesis occurred mostly in young tissues of the shoot and was the major sink of the newly absorbed ^^N-NO3.

SUMMARYAn all glass tight growth chamber, entirely sterilizable, has been constructed to carry out axenic and gnotobiotic cultures of rice plants (Oryza sativa L.). When grown in liquid medium and in the absence of combined nitrogen but in the presence of the diazotrophs Azotobacter vinelandii and Rhodopseudomonas capsulata, rice plants exhibited a complete biological cycle from germination up to ear stage, during a period of time similar to the one encountered in french paddy soil of Camargue. In one experiment, mannitol was given to rice culture medium together with Azotobacter vinelandii and Rhodopseudomonas capsulata. In another experiment, mannitol was not given together with Rhodopseudomonas, and still positive nitrogen gain was obtained, although it was less than culture with mannitol.When 1 s N labeled cells of Rhodopseudomonas were added in rice culture medium, 15N was partly transferred to rice plant. Among the nitrogen substances excreted from the bacteria in the rhizosphere medium, large organic molecules were shown to be the most abundant in our experimental conditions. Moreover, the concentration of free ammonia or aminoacids present in the rice rhizosphere were always compatible with a bacterial nitrogenase activity.

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Abstract. Amide content, ATP level and activities of enzymes linked to malate metabolism were determined in leaves of three successive flushes of common oak during the development of the third flush. In the expanding leaves, all studied enzymes showed a maximum activity around the 7th day after budbreak. Phosphoenolpyruvate carboxylase (PEPc), NAD-malate dehydrogenase (MDH) and NADPmalic enzyme (ME) maintained high activity up to full leaf expansion. In contrast, fumarase (FUM), pyruvate kinase (PK) and NADP-MDH activities sharply decreased to reach, on the 10th day after budbreak, the same low activity levels as those measured in mature leaves. Two patterns were observed in oak leaves during growth. Firstly (7th-10th day after budbreak), PK, FUM and NADP-MDH could contribute to the supply of ATP through glycolysis and Krebs cycle; the ATP profile corroborated those results. Secondly (after the 10th day), the maintenance of an active PEPc pathway led to a respiratory CO2 refixation and provided carbon skeletons for amino acid synthesis. Furthermore, nitrate reductase (NR) activity was high in young oak leaves. Slight changes in activities of NR as well as NAD(P)-ME, NAD(P)-MDH can be noted on days 7 and I0 after budbreak in the mature leaves. These changes could be necessary in supplying the third flush with amino acids. These data suggest that MDH, ME, PK and PEPc have important functions in the young leaves which are not directly linked to C3 photosynthesis but rather to nitrate assimilation and malate provision to mitochondria.