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A minimal model of light-induced circadian rhythms of nitrate reductase activity in leaves of barley
Authors:Cathrine Lillo  Peter Ruoff
Institution:Dept of Botany, Agricultural Univ. of Norway, N-1432 Ás-NLH, Norway.;Rogaland Regional College, Ullandhaug, N-4001 Stavanger, Norway.
Abstract:Observed circadian rhythms of nitrate reductase (NR) (EC 1.6.6.1) activity in leaves of barley ( Hordeum vulgare L. cv. Herta) under continuous light conditions are described by a simple kinetic model. The oscillatory mechanism has been decomposed into the negative and positive feedback loops which are necessary according to present theories of chemical oscillating systems. Our results indicate that the decrease of NR activity in darkness can be considered as a reversible unimolecular conversion of the active form of NR into an inactive form, forming a negative stabilizing feedback loop. The light-induced increase of NR activity is related to a positive destabilizing feedback loop. In our treatment this process is represented as an autocatalytical reaction.
Keywords:Damped oscillations  feedback loops  Hordeum vulgare
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