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Differential effect of ammonium on the induction of nitrate and nitrite reductase activities in roots of barley ( Hordeum vulgare ) seedlings
Author(s) -
Aslam Muhammad,
Travis Robert L.,
Rains D. William,
Huffaker Ray C.
Publication year - 1997
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.1399-3054.1997.tb01045.x
Subject(s) - hordeum vulgare , nitrate reductase , chemistry , ammonium , nitrite , nitrate , nitrite reductase , enzyme , stereochemistry , biochemistry , botany , poaceae , biology , organic chemistry
The effect of exogenous NH 4 + on the induction of nitrate reductase activity (NRA; EC 1.6.6.1) and nitrite reductase activity (NiRA; EC 1.7.7.1) in roots of 8‐day‐old intact barley ( Hordeum vulgare L.) seedlings was studied. Enzyme activities were induced with 0.1, 1 or 10 m M NO 3 + in the presence of 0, 1 or 10 m M NH 4 + , Exogenous NH 4 + partially inhibited the induction of NRA when roots were exposed to 0.1 m M , but not to 1 or 10 m M NO 3 + , In contrast, the induction of NiRA was inhibited by NH 4 + at all NO 3 + levels. Maximum inhibition of the enzyme activities occurred at 1.0 m M NH 4 + Pre‐treatment with NH 4 + had no effect on the subsequent induction of NRA in the absence of additional NH 4 + whereas the induction of NiRA in NH 4 + ‐pretreated roots was inhibited in the absence of NH 4 + At 10 m M NO 3 + L‐methionine sulfoximine stimulated the induction of NRA whether or not exogenous NH 4 + was present. In contrast, the induction of NiRA was inhibited by L‐methionine sulfoximine irrespective of NH 4 + supply. During the postinduction phase, exogenous NH 4 + decreased NRA in roots supplied with 0.1 m M but not with 1m M NH 3 + whereas, NiRA was unaffected by NH 4 + at either substrate concentration. The results indicate that exogenous NH 4 + regulates the induction of NRA in roots by limiting the availability of NO 3 + . Conversely, it has a direct effect, independent of the availability of NO 3 + , on the induction of NiRA. The lack of an NH 4 + effect on NiRA during the postinduction phase is apparently due to a slower turnover rate of that enzyme.