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Effects of the source of inorganic nitrogen on C and N interaction in maize callus tissue: phosphoenolpyruvate carboxylase activity, cytosolic pH and 15 N amino acids
Author(s) -
Amâncio Sara,
Diogo Eugénio,
Santos Helena
Publication year - 1993
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1993.tb05224.x
Subject(s) - phosphoenolpyruvate carboxylase , ammonium , biochemistry , nitrate , callus , amino acid , metabolism , phosphoenolpyruvate carboxykinase , chemistry , biology , enzyme , botany , organic chemistry
The effect of N‐source on the interaction between carbon and nitrogen metabolism was evaluated by measuring phosphoenolpyruvate carboxylase (PEPcase; EC 4.1.1.31) activity in callus tissue of maize ( Zea mays L. cv. Prisma) sub‐cultured under different N‐nutrition conditions: nitrate, ammonium or combinations of both. By comparison with the condition where both salts were supplied (control), nitrate as the sole N‐source led to an increase in PEPcase activity. Ammonium alone gave a drastic decrease of tissue growth. Extracts from calli grown on equivalent media supplied with 15 N‐nitrate or 15 N‐ammonium were analysed by 15 N‐NMR. The labelling of amino acids in the NMR spectra showed that when 15 NO − 3 was the unique N‐source, 15 N mainly accumulated in NδGln, Glu and Ala. With 15 NH + 4 only the NδGln and γ‐aminobutyric acid were labelled. The addition of both gave rise to labelled Gln, Asn, Glu, Asp, Ala, Val and γ‐aminobutyric acid independently of the origin of the label. In vivo 31 P‐NMR allowed the cytoplasmic and vacuolar pH to be measured. The cytoplasmic pH showed an increase of approximately 0.3 units when nitrate was the sole source of nitrogen and a corresponding decrease when ammonium was added alone. Vacuolar pH decreased in both treatments. These results are discussed on the basis of the effect of the N‐source on carbon metabolism. A hypothesis of PEPcase activation as due to the increase of cytoplasmic pH upon nitrate uptake is proposed.