Diurnal variations of nitrite reductase, glutamine synthetase, glutamate synthase, alanine aminotransferase and aspartate aminotransferase in barley leaves

Abstract

LiUo, C. 1984. Diurnal variations of nitrite reductase, glutamiEe synthetase, glutamate synthase, alanine aminotransferase and aspartate aminotransferase in barley leaves. -Physiol. Plant. 61: 214-218.Diurnal variations of in vitro activity of 5 enzymes of nitrogen metabolism were studied. Barley {Hordeum vulgare L. cv. Herta) seedlings were grown in 8 h short days, in daylight or under fluorescent lamps. Daring, the photoperiod nitrite reductase (EC 1.7.7.1) increased by an average of 18% in daylight and 10% under fluorescent lamps. Glutamine synthetase (EC 6.3.1.2) activity increased by 14 and 10%, respectively. The increase in enzyme activity reflected the overall increase in soluble proteins which was 8% in daylight and 3% under fluorescent lamps. Alanine aminotransferase (EC 2.6.1.2) increased by 82% in daylight and 37% under fluorescent lamps. Desalting of the extracts did not alter the enzyme activity and thus supported the assumption that changes in extractable enzyme activity are due to changes in the amount of (active) enzyme protein. Glutamate synthase (EC 1.4.7.1) activity did not show regular diumal variations, and aspartate aminotransferase (EC 2.6.1.1) activity was almost constant.Additional key words -Alanineiglyoxylate aminotransferase, Hordeum vulgare, nitrogen assimilation. leaves have previously been studied (Lillo 1983a), and the objective of the present work was to investigate if the other enzymes in the metabolic pathway show similar variations. In one experiment the extracts were also gel-filtrated in order to reveal activation or inhibition of the enzymes by small molecules in the extract.Abbreviations -y-Gluh, y-glutamylhydroxamate; GOGAT, glutamate synthase; GOT, aspartate aminotransferase; GPT, alanine aminotransferase; OS, glutamine synthetase; NiR, nitrite reductase. Materials and methods Plant materialBarley seeds (Hordeum vulgare L. cv. Herta) were germinated and grown in natural daylight or artifical light Physiol Plant. 61, 1984

Light Regulation of Nitrate uptake, Assimilation and Metabolism

“…Although light did have a positive effect on Fd-GOGAT expression in barley a substantial level of Fd-GOGAT activity was present in the absence of light and also in the absence of nitrate. Early work on Fd-GOGAT activity in barley showed no effects of daily day/night shifts on Fd-GOGAT activity, whereas NR activity varied during the same period (Lillo 1983(Lillo , 1984. In contrast to the situation in Arabidopis, light could not be replaced by sucrose or glucose added to the nutrient solution.…”

“…No positive effect of sugar was found for Fd-GOGAT, although NR activity increased 2-fold in the same experiment. Hence in barley, Fd-GOGAT and NR did not react in parallel in response to the sugar treatment or circadian control (Lillo 1984, Pajuelo et al1997.…”

Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

“…The reactions were stopped, and NO 2 2 was determined following the method established by Hageman (1971). NiR activity measurements were performed according to Lillo (1984).…”

Photosynthetic carbon and nitrogen metabolism and the relationship between their metabolites and lipid peroxidation in dwarf bamboo (Fargesia rufa Yi) during drought and subsequent recovery

“…The homogenate was centrifuged twice at 10,000g for 10 min at 4°C. The supernatant was used to measure the following six enzymes activities (Lillo 1984).…”

“…NiR activity was assayed by monitoring the reduction of NO 2 -using Griess reagent method (Lillo 1984). The reaction mixture contained 100 mM PBS (pH 6.5), 100 mM NaCl, 100 mM NaNO 2 , 100 mM methyl viologen, 100 mM Na 2 S 2 O 4 , and enzyme extract.…”