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The influence of enriched rhizosphere CO 2 on N uptake and metabolism in wild‐type and NR‐deficient barley plants
Author(s) -
Cramer M. D.,
Savidov N. A.,
Lips S. H.
Publication year - 1996
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.1399-3054.1996.tb00477.x
Subject(s) - phosphoenolpyruvate carboxylase , nitrate reductase , hordeum vulgare , rhizosphere , salinity , nitrate , metabolism , chemistry , nitrogen cycle , botany , nitrogen assimilation , carbon dioxide , crassulacean acid metabolism , apoplast , nitrogen , poaceae , photosynthesis , biology , biochemistry , enzyme , ecology , genetics , organic chemistry , bacteria , cell wall
Positive influences of high concentrations of dissolved inorganic carbon (DIC) in the growth medium of salinity‐stressed plants are associated with carbon assimilation through phosphoenolpyruvate carboxylase (PEPc) activity in roots; and also in salinity‐stressed tomato plants, enriched CO 2 in the rhizosphere increases NO − 3 uptake. In the present study, wild‐type and nitrate reductase‐deficient plants of barley ( Hordeum vulgare L. cv. Steptoe) were used to determine whether the influence of enriched CO 2 on NO − 3 uptake and metabolism is dependent on the activity of nitrate reductase (NR) in the plant. Plants grown in NH 4 + and aerated with ambient air, were transferred to either NO 3 − or NH 4 + solutions and aerated with air containing between 0 and 6 500 μmol mol −1 CO 2 . Nitrogen uptake and tissue concentrations of NO 3 − and NH 4 + were measured as well as activities of NR and PEPc. The uptake of NO − 3 by the wild‐type was increased by increasing CO 2 . This was associated with increased in vitro NR activity, but increased uptake of NO 3 − was found also in the NR‐deficient genotype when exposed to high CO 2 concentrations; so that the influence of CO 2 on NO 3 − uptake was independent of the reduction of NO 3 − and assimilation into amino acids. The increase in uptake of NO 3 − in wild‐type plants with enriched CO 2 was the same at pH 7 as at pH 5, indicating that the relative abundance of HCO 3 − or CO 2 in the medium did not influence NO 3 − uptake. Uptake of NH 4 + was decreased by enriched CO 2 in a pH (5 or 7) independent fashion. Thus NO 3 − and NH + 4 uptakes are influenced by the CO 2 component of DIC independently of anaplerotic carbon provision for amino acid synthesis, and CO 2 may directly affect the uptake of NO 3 − and NH 4 + in ways unrelated to the NR activity in the tissue.