Abstract
Winter barley (Hordeum vulgare L cv Igri) plants were grown for 5 weeks in a controlled environment room using a recirculating nutrient solution culture system at a root and shoot temperature of 10ยฐC.
When solution NO~3~โN concentration was varied between 0 and 64 mg litre^โ1^, shoot endogenous and induced nitrate reductase activity (NRA~e~ and NRA~i~ respectively) increased asymptotically from zero in plants grown with O mg NO~3~โN litre^โ1^ to a maximum activity in solutions containing โฉพ 16 mg NO~3~โN litre^โ1^. Shoot Nitrogen Response Index (NRI = NRA~i~/NRA~e~) showed an opposite trend decreasing from a maximum of 2.6 at 2 mg NO~3~โN litre^โ1^ to a minimum approaching unity when โฉพ 32 mg N litre^โ1^ was supplied.
In a separate experiment, nitrogen form (NO~3~โN, NH~4~โN or a 1:1 mixture) had a marked influence on shoot NRA. Enzyme activity was negligible in tissue from plants absorbing NH~4~โN, highest in NO~3~โfed plants and intermediate in those supplied with both N forms. NRI, however, approached unity in all treatments.
The results provide evidence to suggest that NRI may be used as an indicator of the N status of barley plants grown with varied N nutrition.