Are NADP-dependent isocitrate dehydrogenases and ferredoxin-dependent glutamate synthase co-regulated by the same photoreceptors?
Activities of NADP-dependent isocitrate dehydrogenases (cytosolic and plastidic isoforms, ICDH1 and ICDH2; EC 1.1.1.42) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) in turions of Spirodela polyrhiza were all stimulated by light. Single or repeated red light (R) pulses induced the activity of the enzymes and this effect was reverted by subsequent far-red light (FR) pulses. The enzymes are, therefore, co-regulated by the low-fluence response of phytochrome. For ICDH, this is reported here for the first time. Neither an effect of the very low-fluence response nor of the FR-mediated high-irradiance response was detectable. Irradiance with continuous R resulted in enhanced enzyme activities and protein levels (Western analysis using polyclonal antibodies against ICDH1 and Fd-GOGAT). These additional effects of continuous R (called a "non-induction effect") could be inhibited for ICDH1 and ICDH2 by the inhibitor of photosynthetic electron transport, 3-(3',4'-dichlorophenyl)-1,1-dimethylurea, and are therefore related to the effect of photosynthesis. In contrast, the non-induction effect of Fd-GOGAT was resistant against this inhibitor. Moreover, hourly R pulses did not replace the effect of continuous R. The non-induction effect of light on the activity and protein level of Fd-GOGAT was therefore tentatively classified as an R-mediated high-irradiance response. The activity of Fd-GOGAT but not that of ICDHs was additionally regulated by a specific blue-light receptor. It can be concluded that the levels of ICDHs and Fd-GOGAT were coordinated by light but were not co-regulated by the same photoreceptors. Nitrate is necessary for the light regulation of both enzymes, contributing to the coordinated expression of the relevant genes.
Appenroth
Klaus-J
KJ
Institute of General Botany and Plant Physiology, University of Jena, Dornburger Str 159, 07743, Jena, Germany. klaus.appenroth@uni-jena.de
Teller
Steffen
S
D000594:Amino Acid Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D029064:Araceae / Q000187:drug effects / Q000201:enzymology / Q000528:radiation effects; D004237:Diuron / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D007521:Isocitrate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D008027:Light; D009566:Nitrates / Q000494:pharmacology; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D010834:Phytochrome / Q000378:metabolism / Q000528:radiation effects
D009566:Nitrates; D045322:Photosynthetic Reaction Center Complex Proteins; D010834:Phytochrome; D004237:Diuron; D007521:Isocitrate Dehydrogenase; D000594:Amino Acid Oxidoreductases; C042233:glutamate synthase (ferredoxin)