Growth and Nitrate Uptake Properties of Higher Plants: Relations to External and Internal Nitrogen

Larsson, Carl‐Magnus; Oscarson, Petter

doi:10.1007/978-3-642-75812-6_5

Cited by 2 publications

(1 citation statement)

References 13 publications

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“…4B), the difference between the first and last determination being in all cases statistically significant (p ~> 0.99). These values are, however, to be regarded as rough estimates of affinity, probably unrepresentative of the actual influx mechanism (Larsson and Oscarson, 1990). Nevertheless, the K M is of practical use when computing the contributions of seminal roots and crown roots to total uptake (see below).…”

Section: Nitrate Reductase Activitymentioning

confidence: 99%

Growth and development of seminal and crown root systems in N-limited barley, and their contributions to nitrate acquisition during vegetative and generative growth

1993

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Barley (Hordeum vulgare L., cvs Golf and Laevigatum) was grown under nitrogen limitation, controlled by the relative rate of nitrate-N addition (RA), in solution culture. The seminal and crown root systems were kept apart, but in contact with the same nutrient solution throughout culturing. Growth, nitrate uptake, and in vitro nitrate reductase (NR) activity in the different root parts were studied at plant ages from 40 (late vegetative stage) to 110 (mid grain-filling) days. The RA was during this time interval stepwise decreased from 0.08 day -1 to 0.005 day -1. The ratio between seminal root dry weight and total plant dry weight decreased drastically during post-anthesis growth, whereas the contribution by crown roots remained unchanged. Tissue nitrogen concentrations in seminal roots did not change with time, but decreased in crown roots after day 80. The NR activity decreased with age in both seminal and crown roots. The Vma x for net nitrate uptake decreased throughout the experiment in the seminal root system, but not in the crown root system. The kinetic properties (Vma x and KM) were used to calculate the nitrate concentration required to maintain a relative rate of nitrate-N uptake that equals the relative addition rate. These concentrations (2 to 5 mmol m -3) were found to closely match actually measured nitrate concentrations in the nutrient solution (1 to 6 mmol m-3). From uptake kinetics, it was deduced that the contribution by seminal roots to total nitrate uptake at these concentrations decreased from more than 50% in vegetative plants, to about 20% just after main shoot anthesis, and to less than 5% during grain-filling.

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Section: Nitrate Reductase Activitymentioning

confidence: 99%

Growth and development of seminal and crown root systems in N-limited barley, and their contributions to nitrate acquisition during vegetative and generative growth

1993

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The use of natural abundance of nitrogen isotopes in plant physiology and ecology

Handley¹,

Raven

1992

Plant Cell & Environment

527

381

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Nitrogen stable isotope (15N, 14N) natural abundance has been much less used than carbon isotopes (13C, 12C) in plant physiology and ecology. Analytical problems, the lower fractional abundance of 15N than of 13C in the biosphere, the greater complexity of the N cycle relative to the C cycle, and smaller expressed discriminations in nature, are contributing factors. The major N pools, globally, have different isotope signatures: atmospheric N2 is 15N‐depleted relative to organic N (including sedimentary N), a situation resulting from a greater expressed discrimination in the organic N to N2 (via denitrification) reaction than of diazotrophy during accumulation of the reduced N. Essentially all of the enzymes except nitrogenase which transform N compounds show discrimination against 15N, although for glutamine synthetase, and the amination of 2‐oxoglutarate and pyruvate, this is only seen in terms of NH4+ rather than the true substrate, NH3. Discrimination is expressed in various N interconversions within plants, leading to substantial differences in δ15N (up to 12‰) among N compounds and macroscopic plant parts. N isotope fractionation during assimilation of exogenous combined N is often much lower than that expected from studies of isolated enzymes due to processes which show very little discrimination, such as limitation by transport through aqueous solution and membranes. Application of 15N/14N discrimination studies to plant ecology have concentrated largely on distinguishing diazotrophy from N supplied from combined N, based on the lower 15N/14N in diazotrophs due to the higher 15N/14N of combined N sources not being offset by fractionation during uptake. While potentially very useful, a number of pitfalls are discussed in its ecological use in both terrestrial and aquatic systems. N isotope discrimination is also useful in tracking N through food webs, and hence, back to combined N sources for plants.

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Growth and Nitrate Uptake Properties of Higher Plants: Relations to External and Internal Nitrogen

Cited by 2 publications

References 13 publications

Growth and development of seminal and crown root systems in N-limited barley, and their contributions to nitrate acquisition during vegetative and generative growth

Growth and development of seminal and crown root systems in N-limited barley, and their contributions to nitrate acquisition during vegetative and generative growth

The use of natural abundance of nitrogen isotopes in plant physiology and ecology

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