The effects of plant and environmental factors on the nitrate reductase activity of barley, Hordeum vulgare

Sym, Gordon James (1987) The effects of plant and environmental factors on the nitrate reductase activity of barley, Hordeum vulgare. PhD thesis, University of Glasgow.

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The nitrate reductase assay in vivo, and the effects of plant and environmental factors on winter barley nitrate reductase activity were investigated. The work provides a basis for gauging the potential of this biochemical test as an alternative to largely unsuccessful soil and plant tissue tests for predicting field crop nitrogen status and nitrogen fertiliser top-dressing requirements. Nitrate reductase (NR) is the substrate inducible plant enzyme which catalyses the reduction of NO3 to NO2 and is the first, and rate-limiting, step in the biochemical pathway along which NO3 is converted into plant protein. This work describes the development of an assay in vivo for NR involving the incubation of fresh barley shoot, or root, material in darkness in a solution containing buffer, solvent and surfactant. Investigations were carried out to determine the optimum incubation medium composition, pH, temperature and plant material preparation conditions. A large number of other pre-, during and post-incubation factors which influence NO2 production were also investigated. The object of the optimisation procedure was to maximise NOg accumulation during assays and, hence, to develop a rapid, sensitive and reproducible assay method for use in studies of effects of plant and environmental factors on barley NRA. Plant factors investigated included the effects of variety, leaf age, leaf position on the plant and the part of the leaf sampled on barley NRA. Environmental factors studied included effects on NRA in vivo of light conditions (intensity, time after start of photoperiod, darkness), nutrient pH, root and shoot temperatures and, especially, nitrogen nutrition. In the studies of effects of nitrogen nutrition on NRA, factors investigated included rates of induction of NRA by NO3, rates of decline in NRA on withdrawal of NO3 nutrition, influence of NH4 and concentration of NO3 supplied. In many of the above studies, both induced NRA (NRA.) and endogenous NRA (NRAe) values were measured in incubation media with and without added NO3 respectively. Ratios of NRAi to NRAe were calculated to give nitrate assimilation capacity (NAC) values, which more accurately indicated plant N status than either absolute NRAe or NRAi values. NAC values were largely invariant to fluctuations in environmental factors, unlike absolute NRA values which were greatly influenced by many of the plant, environmental and nutritional factors investigated. Finally, a preliminary field study was made of NRA and NAC in a commercially grown winter barley crop. Results were encouraging enough to warrant the proposal of future field studies to extend the use of NRA and NAC measurements from an indicator of crop N status to a commercially useful predictor of optimum rate and time of application of fertiliser N top-dressing.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Plant sciences.
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Hall, Dr. D.A. and Klessa, Dr. D.A.
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-73664
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 09 Jun 2021 14:55

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