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Effects of genetic modification of nitrate reductase expression on 15 NO 3 – uptake and reduction in Nicotiana plants
Author(s) -
Gojon A.,
Dapoigny L.,
Lejay L.,
Tillard P.,
Rufty T.W.
Publication year - 1998
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1998.00269.x
Subject(s) - nitrate reductase , nicotiana tabacum , nicotiana , wild type , solanaceae , biology , horticulture , botany , chemistry , biochemistry , enzyme , mutant , gene
The physiological consequences for NO 3 – utilization by the plant of underexpression and overexpression of nitrate reductase (NR) were investigated in nine transformants of Nicotiana tabacum and Nicotiana plumbaginifolia . The in vitro NR activities (NRAs) in both roots and leaves of low‐ and high‐NR tobacco transformants ranged from 5–10% to 150–200%, respectively, of those measured in wild‐type plants. The level of NR expression markedly affected the NO 3 – reduction efficiency in detached leaves and intact plants. In both species, 15 NO 3 – reduction ranged from 15–45% of 15 NO 3 – uptake in the low‐NR plants, to 40–80% in the wild‐type, and up to 95% in high‐NR plants. In the high‐NR genotypes, however, total 15 NO 3 – assimilation was not significantly increased when compared with that in wild‐type plants, because the higher 15 NO 3 – reduction efficiency was offset by lower 15 NO 3 – uptake by the roots. The inhibition of NO 3 – uptake appeared to be the result of negative feedback regulation of NO 3 – influx, and is interpreted as an adjustment of NO 3 – uptake to prevent excessive amino acid synthesis. In genotypes underexpressing NR, the low 15 NO 3 – reduction efficiency also was generally associated with a decrease in net 15 NO 3 – uptake as compared with the wild type. Thus, underexpression of NR resulted in an inhibition of reduced 15 N synthesis in the plant, although the effect was much less pronounced than that expected from the very low NRAs. The restricted NO 3 – uptake in low‐NR plants emphasizes the point that the products of NO 3 – assimilation are not the only factors responsible for down‐regulation of the NO 3 – uptake system.