|Tucker, Dawn - PLANT BIOLOGY UOFI URBANA|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 25, 2001
Publication Date: N/A
Technical Abstract: NR is the first and rate limiting step in nitrate assimilation. Using NAD(P)H as an electron donor, NR reduces NO3- to NO2- in the cytosol. The enzyme exhibits regulation at the transcript and enzyme level as well as a complex light-induced post-translational modification which dictates its activation state in man7y species studies. This post-translational regulation, accordingly primarily to studies in spinach, entails phosphorylation by a Ca*++ dependent protein kinase; the enzyme is then bound by a 14-3-3 class inhibitor protein in the presence of divalent cations, causing deactivation. This regulatory mechanism is thought to control the activation state of NR during light-dark transitions. Recent literature on regulatory aspects of nitrate reductase indicate that the enzyme's post-translational phosphorylation and subsequent binding of 14-3-3 inhibitor proteins is more complex than once anticipated. Our studies in tomato indicate that NR's diurnal regulation is similar but not identical to that of spinach.