Photoreceptors involved in the regulation of nitrate reductase in Spirodela polyrhiza

✍ Scribed by C. Lillo; F. Provan; K.-J. Appenroth

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 623 KB
• Volume: 44
• Category: Article
• ISSN: 1011-1344
• DOI: 10.1016/s1011-1344(98)00144-4

✦ Synopsis

In green fronds of Spirodela polyrhiza a red-light pulse induces an increase of nitrate reductase (NR) activity. The effect is obtained under optimal assay conditions (absence of Mg 2+ ), therefore reflecting the NR protein level. The effect of a single red-light pulse is reversible by a subsequent far-red pulse, demonstrating the involvement of the photoreceptor phytochrome. Continuous red light applied for 48 h produces a dramatic increase in NR activity which exceeds 25 times the effect of a single red pulse. The threshold value for the induction of NR in continuous red and blue light is 3 txmol m-2 s ~, which coincides with the light compensation point of photosynthesis. In short-term (20 rain) experiments NR is post-translationally activated by photosynthesis, whereas the NR level remains constant. The reduction state of the plastoquinone pool is irrelevant to the signal-transduction chains leading to the changed NR level as well as to post-translational regulation of NR, because blocking the photosynthetic electron transport both before (DCMU) or after (DBMIB) the plastoquinone pool inhibits the induction of NR by light. While it is evident that NR in green fronds of Spirodela polyrhiza is mainly regulated by photosynthesis, the decisive photosynthesis-derived signal is not known.