Appearance of nitrite reductase in cotyledons of the mustard (Sinapis alba L.) seedling as affected by nitrate,phytochrome and photooxidative damage of plastids |
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Authors: | V K Rajasekhar H Mohr |
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Institution: | (1) Biologisches Institut II der Universität, Schänzlestrasse 1, D-7800 Freiburg, Federal Republic of Germany |
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Abstract: | Nitrite reductase (NIR; EC 1.7.7.1) is a central enzyme in nitrate assimilation and is localized in plastids. The present study concerns the regulation of the appearance of NIR in cotyledons of the mustard (Sinapis alba L.) seedling. It was shown that light exerts its positive control over the nitrate-mediated induction of NIR via the farred-absorbing form of phytochrome. Without nitrate the light effect cannot express itself; even though the light signal is accumulated in the cotyledons it remains totally cryptic in the absence of nitrate. Moreover, it was recognised that intact plastids are important in the control of the appearance of NIR. If the plastids are damaged by photooxidation the action of nitrate and phytochrome on NIR appearance is abolished. The appearance of nitrate reductase (NR; EC 1.6.6.1) responds similarly to photooxidative damage even though this enzyme is cytosolic. While the data strongly indicate that some plastidic signal is a prerequisite for the nitrate-induced and phytochrome-modulated appearance of NIR and NR, the possibility could not be ruled out that photooxidative damage affects the accumulation of NIR in the organelle.Abbreviations c
continuous
- D
darkness
- FR
far-red light
- NADP-GPD
NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.1.13)
- NF
Norflurazon
- NIR
nitrite reductase (EC 1.7.7.1.)
- NR
nitrate reductase (EC 1.6.6.1)
- Pfr
phytochrome (far-red light obtained with RG9 glass filter
- R
red light
- RG9-light
long wavelenght far-red light obtained with RG9 glass filter
- RuBPCase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
- WL
white light
- WLs
strong white light (28 W m-2) |
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Keywords: | Nitrate assimilation Nitrate reductase Nitrite reductase Phytochrome Plastidic signal Sinapis |
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