Short-term modulation of nitrate reductase activity by exogenous nitrate in Nicotiana plumbaginifolia and Zea mays leaves

Abstract

Abstract.Maize (Zea mays L.) grown on low (0.8 raM) NO;-, as well as untransformed and transformed Nicotiana plumbaginifolia constitutively expressing nitrate reductase (NR), was used to study the effects of NO~ on the NR activation state. The NR activation state was determined from the relationship of total activity extracted in the presence of ethylenediaminetetracetic acid to that extracted in the presence of Mg 2+. Light activation was observed in both maize and tobacco leaves. In the tobacco lines, NO3 did not influence the NR activation state. In excised maize leaves, no correlation was found between the foliar NO~ content and the NR activation state. Similarly, the NR activation state did not respond to NOj. Since the NR activation state determined from the degree of Mg 2 +-induced inhibition of NR activity is considered to reflect the phosphorylation state of the NR protein, the protein phosphatase inhibitor microcystin LR was used to test the importance of protein phosphorylation in the NO~-induced changes in NR activity. In-vivo inhibition of endogenous protein phosphatase activity by microcystin-LR decreased the level of NR activation in the light. This occurred to the same extent in the presence or absence of exogenous NO3. We conclude that NO3 does not effect the NR activation state, as modulated by protein phosphorylation in either tobacco (a C3 species) or maize (a C4 species). The short-term regulation of NR therefore differs from the NO~--mediated responses observed for phosphoenolpyruvate carboxylase and sucrose phosphate synthase.

Boron deficiency decreases plasmalemma H+-ATPase expression and nitrate uptake, and promotes ammonium assimilation into asparagine in tobacco roots

“…4a, 7a). Thus, as previously described by other authors (Ferrario et al 1996;Scheible et al 1997b;Man et al 1999), there were no evidences for a relation between the tissue nitrate concentration and the post-transcriptional regulation of NR. There was no correlation between NR activity and NIA transcript levels either (Galangau et al 1988).…”

Sucrose-feeding leads to increased rates of nitrate assimilation, increased rates of α-oxoglutarate synthesis, and increased synthesis of a wide spectrum of amino acids in tobacco leaves

“…Nitrate-feeding led to only a slight and non-signi®cant increase of NR activation ( Fig. 1D; see also Ferrario et al 1996).…”

Modulation of carbon and nitrogen metabolism, and of nitrate reductase, in untransformed and transformed Nicotiana plumbaginifolia during CO 2 enrichment of plants grown in pots and in hydroponic culture

“…Figure 3B demonstrates that in three dierent 35S-GUS transformants with dierent intrinsic levels of GUS expression the ratio of GUS expression to GUS activity was constant such that an increase in GUS mRNA was accompanied by an increase in GUS activity both in air and at high CO 2 . Dierences in the NR activation state in dierent lines over the photoperiod were slight (Ferrario et al 1996). The NR activation state was decreased in the roots and shoots of the untransformed plants grown in hydroponic culture at high CO 2 (Table 6A) but no dierences were observed in either the roots or shoots of the 35S transformants.…”