Effects of Nitrate and Ammonium on Gene Expression of Phosphoenolpyruvate Carboxylase and Nitrogen Metabolism in Maize Leaf Tissue during Recovery from Nitrogen Stress

Abstract

We previously showed that the selective accumulation of phosphoenolpyruvate carboxylase (PEPC) in photosynthetically maturing maize (Zea mays L.) leaf cells induced by nitrate supply to nitrogen-starved plants was primarily a consequence of the level of its mRNA (B Sugiharto, K Miyata, H Nakamoto, H Sasakawa, T Sugiyama [1990] Plant Physiol 92: 963-969). To determine the specificity of inorganic nitrogen sources for the regulation of PEPC gene expression, nitrate (16 millimolar) or ammonium (6 millimolar) was supplied to plants grown previously in low nitrate (0.8 millimolar), and changes in the level of PEPC and its mRNA were measured in the basal region of the youngest, fully developed leaves of plants during recovery from nitrogen stress. The exogenous supply of nitrogen selectively increased the levels of protein and mRNA for PEPC. This increase was more pronounced in plants supplemented with ammonium than with nitrate. The accumulation of PEPC during nitrogen recovery increased in parallel with the increase in the activity of glutamine synthetase and/or ferredoxin-dependent glutamate synthase. Among the major amino acids, glutamine was the most influenced during recovery, and its level increased in parallel with the steady-state level of PEPC mRNA for 7 hours after nitrogen supply. The administration of glutamine (12 millimolar) to nitrogen-starved plants increased the steady-state level of PEPC mRNA 7 hours after administration, whereas 12 millimolar glutamate decreased the level of PEPC mRNA. The results indicate that glutamine and/ or its metabolite(s) can be a positive control on the nitrogendependent regulation of PEPC gene expression in maize leaf cells.skeletons for ammonium assimilation (3, 15), and (c) synthesis of organic acids to maintain charge balance (7,19). It is therefore not surprising that the enzyme plays a central metabolic role in carbon and nitrogen interaction in plants.Nitrogen is an important regulator of not only carbon flow but also the gene expression of some proteins in higher plants and algae through mechanisms affecting transcription and/or mRNA stability. These proteins include NR and nitrite reductase (1), Chl a/b light-harvesting complex apoproteins (13), vegetative storage proteins (16), and PEPC (17,23). When maize plants are grown under conditions of nitrogen starvation, the levels of PEPC protein are selectively reduced most conspicuously in the photosynthetic maturing leaf cells primarily as a consequence of the level of PEPC mRNA (17). Despite the major effects of nitrogen on these proteins, information concerning nitrogen availability in the regulation of their gene expression is meager.In the present study, we measured the total pool sizes of the potentially important cellular metabolites involved in nitrogen/carbon assimilations correlating with the nitrogendependent induction of PEPC mRNA in the photosynthetically maturing leaf cells of maize plants during recovery from nitrogen starvation. The objectives were to determine: (a) the specificity of nitrogen ...

Effects of different ammoniacal nitrogen sources on N-metabolism of the atmospheric bromeliad Tillandsia pohliana Mez

“…The amino acid, which is often present in greater proportions, as a result of an increase in N concentration, is glutamine, as reported by Barneix et al (1984) in barley (Hordeum vulgare L. cv. Sonja), and by Sugiharto & Sugiyama (1992) in maize (Zea mays L.).…”

Developmental regulation of photosynthate distribution in leaves of rice

“…The relative expression levels of each mRNA were similar in leaves of different ages, except for the PEPC mRNA, which accumulated more strongly in leaves at late growth stages. Since ammonium and glutamine activate PEPC mRNA expression (Sugiharto et al 1992), nitrogenous compounds derived from protein degradation during leaf senescence must be expected to stimulate PEPC mRNA expression.…”

Cytokinin Is Required to Induce the Nitrogen-Dependent Accumulation of mRNAs for Phosphoenolpyruvate Carboxylase and Carbonic Anhydrase in Detached Maize Leaves

“…We previously studied the N-dependent expression of the photosynthetically important PEPC gene using an attached leaf of maize plants (11,12). To study the mechanism under- (Fig.…”

“…With regard to the regulation by nitrogen, the expression of the PEPC gene is influenced by N availability in a maize Zea mays L. leaf, presumably at the level of transcription and/or the stability of mRNA (11,12). In addition, the mechanism controlling the expression of maize leaf PEPC and CA activity, key enzymes in the C4 pathway, are closely related (2).…”

“…To identify a possible messenger(s) in the N-dependent gene expression of maize C4v enzymes, which mediates the communication between leaf and root tissues, we have chosen detached maize leaves as the experimental material. Two important questions arise in this respect: (a) How is the appearance of N-dependent gene expression in (11,12). The youngest, fully developed leaves, i.e.…”