ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Control by light and nitrate of the appearance of nitrite reductase (NIR; EC 1.7.7.1) activity was investigated in turions of Spirodela polyrhiza during the pre-germination period to establish the nature of the coaction between these factors. A cDNA clone coding for tobacco NIR was available as a probe. In the period immediately after transfer from after-ripening conditions (5°C. darkness) to germination conditions (25°C; phase 1, from 0 to 72 h after start of the experiments) a nitrate-dependent increase in NIR activity was observed, presumably because of the temperature shift. During this phase light had no effect on the nitrate-dependent increase in NIR activity. In contrast, after a pre-treatment of 72 h in darkness at 25°C following cold afterripening responsiveness to phytochrome appeared, with light inducing a nitrate-dependent increase in NIR activity (phase II, from 72 to 120 h after start of the experiments). Application of nitrate (10 mM) in phase II also resulted in an increase of NIR activity in light or darkness although highest NIR activities were observed in the presence of light. Ammonium did not affect the appearance of NIR activity. In all experiments, a single isoform of NIR was detectable in both phases. It was concluded that the mode of coaction between light (via phytochrome) and nitrate is different in phase I and phase II and depends on the developmental state of the plant organs. Furthermore, the response patterns of nitrate reductase and NIR activities to both factors is so similar in turions that co-regulation of both enzymes can be assumed, as found previously in tobacco seedlings. Northern blot analyses revealed a low NIR transcript level in the absence of nitrate in darkness during phase II. Both light and nitrate alone were sufficient to stimulate the NIR mRNA steady state level and the highest transcript level was detectable in the presence of both stimulators. This demonstrates a synergistic effect of both factors on steady state NIR transcript level.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1995.tb02228.x
Permalink
