Ammonia Fixation via Glutamine Synthetase and Glutamate Synthase in the CAM Plant Cissus quadrangularis L.

Abstract

In a variety of C3 and C4 photosynthetic tissues it is widely recognized that ammonia assimilation proceeds via 9,28,29 To avoid infestation by fungus, the plants were watered twice (0.75 L per tray) with orthocid 50 (3 g captan/L) and also sprayed with the fungicide about 8 weeks prior to use.CO2 and H20 Gas Exchange Measurements. An open gas exchange system (2) was modified to simultaneously measure 3 samples. The CO2 concentration of the measuring gas was adjusted by mixing CO2 free air with CO2 using mass flow controllers (FC 2600, Tylan GmbH, D-8057 Eching). The gas stream was divided. The reference gas was dried and passed through the reference side of the CO2 gas analyzer (22 L/h). Internodes were enclosed in a tube shaped plexiglass cuvette (length 300 mm, internal diameter 32 mm). Four tubes were embedded in a closed water bath (about 10 mm water layer over the tubes) to control cuvette temperature. Each tube was flushed with 60 L/h of humidifed air (100% RH at 12.5C). The gas flow rates in the individual cuvettes were measured by flowmeters (Platon Flowbits GmbH, D-6903 Neckargemund and Rota D-7012 Oelflingen). Constant pressure conditions enabling constant gas fluxes through the cuvettes were obtained by bubbling excess gas into water (water column about 50 mm) using magnetic three way valves. The gas stream of one cuvette was led every 10 min to the humidity sensor (Vaisala, Driesen und Kern, D-2000 Hamburg-Tangstedt) and dried over CaCI2 and Mg(Cl04)2 before measuring the CO2 concentration with an IR gas analyzer (Unor 2, Maihak, D-2000 Hamburg). The temperature of the plant material was measured using two cooper constantan wires attached to the lower surfaces of two stem sections.The rates of CO2 uptake and evaporation were calculated as described previously (2).Experimental.

Effect of Methionine Sulfoximine on Nitrogen Metabolism and Externally Supplied Ammonium Assimilation in Kidney Bean

“…This fact might be explained by relatively high specific activity of GDH under these conditions. The increase of the amount of ammonia as a result of GS inhibition has also been detected by other authors (Stewart and Rhodes, 1976;Berger and Sprengart, 1986). The accumulation of ammonia in relatively high amounts in roots and leaves in the case of 3-hr exposure after infiltration of ammonium sulfate only is apparently caused by relatively low GS activity at this time.…”

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MSO and azaserine (specific inhibitor of GOGAT) provided L-Methionine sulfoximine (MSO) at concentration 1.25 mM in evidence of the key role of these enzymes in the assimilation vivo causes the inhibition of glutamine synthetase (GS) in both of ammonium in higher plants (Stewart and Rhodes, 1976; roots and leaves of young seedlings of kidney bean following the Berger and Sprengart, 1986). It has been suggested that the accumulation of high levels of ammonia and decrease in amounts role of GDH, which catalyzes the reductive amination reacof free amino acids that is more pronounced in leaves.

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15N NUCLEAR MAGNETIC RESONANCE STUDY OF AMMONIUM ION ASSIMILATION BY LEMNA GIBBA L.

“…However, ammonium ions can also be used as a source of nitrogen by some higher plants in which they are taken up at similar or even at higher rates than nitrate. For many years the assimilation of ammonia in plants was thought to be mediated by the GDH (glutamate dehydrogenase) pathway (Folkes & Yemm, 1958;Singh & Srivastava, 1982;Quetz, Tischner & Lorenzen, 1982;Cammaerts & Jacobs, 1985), but more recently an alternative GS/GOGAT pathway has been established (Lea & Miflin, 1974;Miflin & Lea, 1980;Woo & Osmond, 1982;Berger et al, 1986).…”