Abstract
The influence of NH4+ And NO3- on the activity of nitrate reductase (NR; EC 1. 6.6.1) and the level of the molybdenum cofactor (MoCo) was studied in annual ryegrass (Lolium multiflorum cv Westerwoldicum). Addition of 4.5 mM NH4+ to plants grown with NO3- increased NR activity in the shoots, but decreased it in the root. Total MoCo increased in both roots and shoots. Plants grown with only NH4- increased their MoCo content with N concentration in the medium, while NR activity remained at constitutive levels. NR activity, total MoCo content, readily available MoCo (determined without a heat pretreatment) and NO3- accumulation increased in plant root and shoot within 1 day in NO3-. NH4+ triggered the increase of total and readily available MoCo content in shoot and root above the constitutive level after 1 day of induction. MoCo biosynthesis may be regulated by NH4+ and NO3- or one of their common assimilation products. N-regulation of MoCo in the roots differs from the shoots in that: (a) total root MoCo increased proportionally more than NR in plants grown with NO3-, while total shoot MoCo and NR activity levels were quite similar; and (b) The NH4+ induced increase in MoCo was proportionally higher in roots than in shoots, suggesting a higher demand of MoCo in the root for the biosynthesis of molybdo-enzymes other than NR.
Original language | English |
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Pages (from-to) | 17-24 |
Number of pages | 8 |
Journal | Plant Science |
Volume | 135 |
Issue number | 1 |
DOIs | |
State | Published - 22 Jun 1998 |
Keywords
- Ammonium
- Lolium
- Molybdenum cofactor
- Nitrate
- Nitrate reductase
- Ryegrass
ASJC Scopus subject areas
- Genetics
- Agronomy and Crop Science
- Plant Science