Abstract
Mutants and transformants of tobacco ( Nicotiania tabacum L. cv Gatersleben 1) with decreased expression of nitrate reductase have been used to investigate whether nitrate accumulation in the shoot acts as a signal to alter allocation between shoot and root growth. (a) Transformants with very low (1–3% of wild‐type levels) nitrate reductase activity had growth rates, and protein, amino acid and glutamine levels similar to or slightly lower than a nitrate‐limited wild‐type, but accumulated large amounts of nitrate. These plants should resemble a nitrate‐limited wild‐type, except in responses where nitrate acts as a signal. (b) Whereas the shoot:root ratio decreases from about 3.5 in a well‐fertilized wild‐type to about 2 in a nitrate‐limited wild‐type, the transformants had a very high shoot:root ratio (8–10) when they were grown on high nitrate. When they were grown on lower nitrate concentrations their shoot:root ratio declined progressively to a value similar to that in nitrate‐limited wild‐types. Mutants with a moderate (30–50%) decrease of nitrate reductase also had a small but highly significant increase of their shoot:root ratio, compared to the wild‐type. The increased shoot:root ratio in the mutants and transformants was due to a stimulation of shoot growth and an inhibition of root growth. (c) There was a highly significant correlation between leaf nitrate content and the shoot:root ratio for eight genotypes growing at a wide range of nitrate supply. (d) A similar increase of the shoot:root ratio in nitrate reductase‐deficient plants, and correlation between leaf nitrate content and the shoot:root ratio, was found in plants growing on ammonium nitrate. (f) Split‐root experiments, in which the transformants were grown with part of their root system in high nitrate and the other part in low nitrate, showed that root growth is inhibited by the accumulation of nitrate in the shoot. High concentrations of nitrate in the rooting medium actually stimulate local root growth. (g) The inhibition of root growth in the transformants was relieved when the transformants were grown on limiting phosphate, even though the nitrate content of the root remained high. This shows that the nitrate‐dependent changes in allocation can be overridden by other signals that increase allocation to root growth. (h) The reasons for the changed allocation were investigated in transformants growing normally, and in split‐root culture. Accumulation of nitrate in the shoot did not lead to decreased levels of amino acids or protein in the roots. However, it did lead to a strong inhibition of starch synthesis and turnover in the leaves, and to decreased levels of sugars in the root. The rate of root growth was correlated with the root sugar content. It is concluded that these changes of carbon allocation could contribute to the changes in shoot and root growth.
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Claims 19
Claim · model-written summary
Low nitrate reductase transformants had growth and protein, amino acid and glutamine levels similar to or slightly lower than nitrate-limited wild type.
- Taxon
- tobacco
Nicotiana tabacumt0 - Material
- Transformantse0
- Gene
- nitrate reductasee0
- Outcome
- growth rates, and protein, amino acid and glutamine levelse0
- Direction
- similar to or slightly lowere0
- Value
- 1–3% of wild‐type levelse0
- Comparator
- nitrate‐limited wild‐typee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Transformants with very low (1–3% of wild‐type levels) nitrate reductase activity had growth rates, and protein, amino acid and glutamine levels similar to or slightly lower than a nitrate‐limited wild‐type”
t0“tobacco”
Claim · model-written summary
Low nitrate reductase transformants accumulated large amounts of nitrate.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- nitratee0
- Direction
- accumulated large amountse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but accumulated large amounts of nitrate”
t0“tobacco”
Claim · model-written summary
Wild-type shoot:root ratio fell from about 3.5 under full fertilization to about 2 under nitrate limitation.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- shoot:root ratioe0
- Direction
- decreasese0
- Value
- about 3.5e0
- Qualifier
- about 2e0
- Comparator
- nitrate‐limited wild‐typee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the shoot:root ratio decreases from about 3.5 in a well‐fertilized wild‐type to about 2 in a nitrate‐limited wild‐type”
t0“tobacco”
Claim · model-written summary
Transformants had shoot:root ratios of 8–10 on high nitrate.
- Taxon
- tobaccoNicotiana tabacumt0
- Material
- transformantse0
- Outcome
- shoot:root ratioe0
- Direction
- very highe0
- Value
- 8–10e0
- Qualifier
- high nitratee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the transformants had a very high shoot:root ratio (8–10) when they were grown on high nitrate”
t0“tobacco”
Claim · model-written summary
Transformant shoot:root ratio declined progressively with lower nitrate.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- shoot:root ratioe0
- Direction
- declined progressivelye0
- Comparator
- nitrate‐limited wild‐typese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When they were grown on lower nitrate concentrations their shoot:root ratio declined progressively to a value similar to that in nitrate‐limited wild‐types”
t0“tobacco”
Claim · model-written summary
Moderate nitrate reductase mutants had a small but highly significant increase in shoot:root ratio versus wild type.
- Taxon
- tobaccoNicotiana tabacumt0
- Material
- Mutantse0
- Gene
- nitrate reductasee0
- Outcome
- shoot:root ratioe0
- Direction
- increasee0
- Value
- 30–50%e0
- Comparator
- wild‐typee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Mutants with a moderate (30–50%) decrease of nitrate reductase also had a small but highly significant increase of their shoot:root ratio, compared to the wild‐type”
t0“tobacco”
Claim · model-written summary
In mutants and transformants, increased shoot:root ratio reflected stimulated shoot growth.
- Taxon
- tobaccoNicotiana tabacumt0
- Material
- mutants and transformantse0
- Outcome
- stimulation of shoot growthe0
- Direction
- stimulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The increased shoot:root ratio in the mutants and transformants was due to a stimulation of shoot growth and an inhibition of root growth”
t0“tobacco”
Claim · model-written summary
In mutants and transformants, increased shoot:root ratio reflected inhibited root growth.
- Taxon
- tobaccoNicotiana tabacumt0
- Material
- mutants and transformantse0
- Outcome
- inhibition of root growthe0
- Direction
- inhibitione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The increased shoot:root ratio in the mutants and transformants was due to a stimulation of shoot growth and an inhibition of root growth”
t0“tobacco”
Claim · model-written summary
Leaf nitrate content correlated significantly with shoot:root ratio across eight genotypes and nitrate supplies.
- Taxon
- tobaccoNicotiana tabacumt0
- Compound
- leaf nitrate contente0
- Outcome
- shoot:root ratioe0
- Qualifier
- eight genotypes growing at a wide range of nitrate supplye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There was a highly significant correlation between leaf nitrate content and the shoot:root ratio for eight genotypes growing at a wide range of nitrate supply”
t0“tobacco”
Claim · model-written summary
Nitrate reductase deficient plants on ammonium nitrate likewise had an increased shoot:root ratio.
- Taxon
- tobaccoNicotiana tabacumt0
- Gene
- nitrate reductasee0
- Outcome
- shoot:root ratioe0
- Direction
- increasee0
- Qualifier
- ammonium nitratee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A similar increase of the shoot:root ratio in nitrate reductase‐deficient plants, and correlation between leaf nitrate content and the shoot:root ratio, was found in plants growing on ammonium nitrate”
t0“tobacco”
Claim · model-written summary
On ammonium nitrate, leaf nitrate content correlated with shoot:root ratio.
- Taxon
- tobaccoNicotiana tabacumt0
- Compound
- leaf nitrate contente0
- Outcome
- shoot:root ratioe0
- Qualifier
- ammonium nitratee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“correlation between leaf nitrate content and the shoot:root ratio, was found in plants growing on ammonium nitrate”
t0“tobacco”
Claim · model-written summary
Split-root experiments showed that shoot nitrate accumulation inhibits root growth.
- Taxon
- tobaccoNicotiana tabacumt0
- Compound
- nitratee0
- Outcome
- root growthe0
- Direction
- inhibitede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“root growth is inhibited by the accumulation of nitrate in the shoot”
t0“tobacco”
Claim · model-written summary
High nitrate concentrations in rooting medium stimulated local root growth.
- Taxon
- tobaccoNicotiana tabacumt0
- Treatment
- High concentrations of nitrate in the rooting mediume0
- Outcome
- local root growthe0
- Direction
- stimulatee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High concentrations of nitrate in the rooting medium actually stimulate local root growth”
t0“tobacco”
Claim · model-written summary
Limiting phosphate relieved root-growth inhibition in transformants despite high root nitrate.
- Taxon
- tobaccoNicotiana tabacumt0
- Treatment
- limiting phosphatee0
- Outcome
- inhibition of root growthe0
- Direction
- relievede0
- Qualifier
- nitrate content of the root remained highe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The inhibition of root growth in the transformants was relieved when the transformants were grown on limiting phosphate, even though the nitrate content of the root remained high”
t0“tobacco”
Claim · model-written summary
Shoot nitrate accumulation did not lower root amino acid and protein levels.
- Taxon
- tobaccoNicotiana tabacumt0
- Compound
- nitratee0
- Outcome
- levels of amino acids or protein in the rootse0
- Direction
- did not lead to decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Accumulation of nitrate in the shoot did not lead to decreased levels of amino acids or protein in the roots”
t0“tobacco”
Claim · model-written summary
Shoot nitrate accumulation strongly inhibited leaf starch synthesis and turnover.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- starch synthesis and turnover in the leavese0
- Direction
- inhibitione0
- Qualifier
- in the leavese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“it did lead to a strong inhibition of starch synthesis and turnover in the leaves”
t0“tobacco”
Claim · model-written summary
Shoot nitrate accumulation decreased root sugar levels.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- levels of sugars in the roote0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“and to decreased levels of sugars in the root”
t0“tobacco”
Claim · model-written summary
Root growth rate correlated with root sugar content.
- Taxon
- tobaccoNicotiana tabacumt0
- Compound
- root sugar contente0
- Outcome
- rate of root growthe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The rate of root growth was correlated with the root sugar content”
t0“tobacco”
Claim · model-written summary
The authors conclude carbon allocation changes may contribute to altered shoot and root growth.
- Taxon
- tobaccoNicotiana tabacumt0
- Outcome
- changes in shoot and root growthe0
- Qualifier
- changes of carbon allocatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“these changes of carbon allocation could contribute to the changes in shoot and root growth”
t0“tobacco”
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