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. 1982 Dec;70(6):1683–1688. doi: 10.1104/pp.70.6.1683

Rhythms in Glutamine Synthetase Activity, Energy Charge, and Glutamine in Sunflower Roots 1

Thomas J Knight 1,2,2, Gerard S Weissman 1,2
PMCID: PMC1065955  PMID: 16662744

Abstract

Roots of sunflower plants (Helianthus annuus L. var. Mammoth Russian) subjected to L12: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+½ADP/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.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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