Rhythms in Glutamine Synthetase Activity, Energy Charge, and Glutamine in Sunflower Roots

Abstract

Roots of sunflower plants (Helianthus anus L. var. Mammoth Russian) subjected to ,12:D12, L18:D6, and L12:D12 followed by continuous light all display rhythms of about 12 hours for glutamine synthetase (GS) activity (transferase reaction) with one peak in the 'light phase' and one in the 'dark phase.' Root energy charge (EC = ATP+%ADP/ ATP+ADP+AMP) is directly correlated with GS, but the GS rhythm is better explained as the result of a rhythmic adenine nucleotide ratio (ATP/ ADP+AMP) that regulates enzyme activity through allosteric modification. When L12:D12 plants are subjected to free-running conditions in continuous darkness, only diurnal rhythms for GS and EC, with peaks in the dark phase, remain. The 12-hour root rhythms for GS and EC appear to be composed of two alternating rhythms, one a diurnal, light-dependent, incompletely circadian light phase rhythm and the other a light-independent, circadian dark phase rhythm.Only glutamine, of the root amino acids, displays cyclical changes in concentration, maintaining under all conditions a 12-hour rhythm that is consistently synchronized with, but nearly always inversely correlated with, GS and EC rhythms.The phenomenon of endogenous biological oscillation in plants has been found to occur at all levels of organization: organ, cells, organelle, and enzyme (7). Almost universally, the light:dark regimen has been identified as the entraining factor and numerous examples of light-entrainable rhythms have been reported for physiological or biochemical processes in higher plants (14). Most rhythms appear to be circadian with periodicities under freerunning conditions ofapproximately 24 h. Also reported, however, are rhythms with a period clearly less than 24 h and these have been termed 'ultradian' (10). In view of the correlation demonstrated in this laboratory (34) between the activity of sunflower root GS3 and energy charge as defined by Atkinson (2) investigation in which an effort has been made to determine whether energy charge and GS vary in a cyclical manner in sunflower roots, a portion of the plant not expected to be directly affected by light functioning as a 'Zeitgeber.' In view of the fact that previous studies have indicated a role for amino acids in the regulation of higher plant GS (22, 27), we have also examined variations in the concentrations of these substances in sunflower roots with respect to rhythmicity. MATERIALS AND METHODSPlant Culture. Sunflower seeds (Helianthus annus L. var. Mammoth Russian) were germinated in vermiculite in a controlled temperature chamber (26-27°C) under artificial light with a light:dark regimen specific to a particular experiment (L12:D12, L18:D6). Eight-d-old seedlings were transferred to a previously described (35) continuous flow apparatus that provided enclosure of the root system in blackened tubes. Complete culture solution containing nitrogen as 10 mm NO3 was allowed to pass over the roots for the remainder of the growth period. On day 28, the plants, having previously been subjected to a specific l...

Clock Gene Dysregulation Induced by Chronic ER Stress Disrupts β-cell Function

“…The ATP/ADP ratios in cyanobacterial cells and sunflower roots are actually higher in the dark than in the light and oscillate in a circadian manner (Pattanayak et al, 2014, Knight and Weissman, 1982). In mouse islets, the basal ATP/ADP ratio exhibits circadian oscillation associated with overall DBP activity (Fig.…”

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

“…In sunflower roots the GS activity varied manifold over a few hours (Knight and Weissman 1982). There were no indications of such great variations of GS ac-tivity in barley leaves.…”

Effect of light‐dark transition on glutamine synthetase activity in tomato leaves

“…Glutamine synthetase activity was high in tomato leaves and low in roots, cotyledons and shoots (Tab, 1). The lack of glutamine synthetase activity in roots was sur- prising since the extracts were obtained from plants supplied with ammonium nitrate and the ammonium ion is not generally found in the xylem fluid leaving the roots (Miflin et al, 1981), Moreover, glutamine synthetase activity has been found in roots of barley (Mann et al, 1979), rice (Iyer et al, 1981) and sunflower (Knight and Weissman 1982), In rice roots, the activity was even higher than in leaves. However, in both barley and rice plants, the root enzymes are very similar to the cytosolic leaf enzyme, which is not found in tomato leaves , Glutamine synthetase of tomato roots is probably very unstable and some proteolytic degradation may occur during the extraction procedure, even in the presence of PMSF, Glutaraate dehydrogenase activity was high in tomato roots, but low in cotyledons, shoot and leaves (Tab, 1), It seems likely that in the roots of plants supplied with ammonium, glutamate dehydrogeoase has an assimilatory function.…”

“…In Lemna minor a reduction in glutamine synthetase levels has been reported to occur after transferring the plants from light to dark (Rhodes et al, 1977), A similar direct relationship between glutamine synthetase activity and light levels was found during the greening of etiolated rice plants (Hirel et al 1982) and pumpkins (Evstigneeva et al, 1981, Nishimura et al, 1982, More specifically, the increase in glutamine synthetase activity occurred io the chloroplast compartment whereas decreases in cytosolic gliitamine synthetase activity were found during rice leaf greening. These changes in glutamine synthetase have sometimes heen explained as feed-back inhibition by amino acids, the concentrations of which change with transition from dark to light in pea leaves (Bauer et al 1977) and sunflower roots (Knight and Weissman 1982). This does not appear to be valid for tomato leaves since the inhibitory effects of amino acids on glutamine syothetase in vitro are very small (Caoovas et al 1984).…”