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C. Meyer

Publications and source records attributed to C. Meyer.

3 recordsLinked to original sources
PubMed1997

Characterization of Nitrate Reductase from Light- and Dark-Exposed Leaves (Comparison of Different Species and Effects of 14-3-3 Inhibitor Proteins).

Nitrate reductase (NR) was extracted and partially purified from leaves of squash (Curcurbita maxima), spinach (Spinacia oleracea), and three transgenic Nicotiana plumbaginifolia leaves in the presence of phosphatase inhibitors to preserve its phosphorylation state. Purified squash NR showed activation by substrates (hysteresis) when prepared from leaves in the light as well as in darkness. A 14-3-3 protein known to inhibit phosphorylated spinach NR in the presence of Mg2+ decreased by 70 to 85% the activity of purified NR from dark-exposed leaves, whereas NR from light-exposed leaves decreased by 10 to 25%. Apparent lack of posttranslational NR regulation in a transgenic N. plumbaginifolia expressing an NR construct with an N-terminal deletion ([delta]NR) may be explained by more easy dissociation of 14-3-3 proteins from [delta]NR. Partially purified [delta]NR was, however, inhibited by 14-3-3 protein, and the binding constant of 14-3-3 protein (4 x 108 M-1) and the NR-inhibiting protein concentration that results in a 50% reduction of free NR (2.5 nM) were the same for NR and [delta]NR. Regulation of NR activity by phosphorylation and binding of 14-3-3 protein was a general feature for all plants tested, whereas activation by substrates as a possible regulation mechanism was verified only for squash.

Journal Article↗
PubMed1997

Abolition of Posttranscriptional Regulation of Nitrate Reductase Partially Prevents the Decrease in Leaf NO3- Reduction when Photosynthesis Is Inhibited by CO2 Deprivation, but Not in Darkness.

The activity of nitrate reductase (NR) in leaves is regulated by light and photosynthesis at transcriptional and posttranscriptional levels. To understand the physiological role of these controls, we have investigated the effects of light and CO2 on in vivo NO3- reduction in transgenic plants of Nicotiana plumbaginifolia lacking either transcriptional regulation alone or transcriptional and posttranscriptional regulation of NR. The abolition of both levels of NR regulation did not modify the light/dark changes in exogenous 15NO3- reduction in either intact plants or detached leaves. The same result was obtained for 15N incorporation into free amino acids in leaves after 15NO3- was supplied to the roots, and for reduction of endogenous NO3- after transfer of the plants to an N-deprived solution. In the light, however, deregulation of NR at the posttranscriptional level partially prevented the inhibition of leaf 15NO3- reduction resulting from the removal of CO2 from the atmosphere We concluded from these observations that in our conditions deregulation of NR in the transformants investigated had little impact on the adverse effect of darkness on leaf NO3- reduction, and that posttranscriptional regulation of NR is one of the mechanisms responsible for the short-term coupling between photosynthesis and leaf NO3- reduction in the light.

Journal Article↗