Abstract
It has been shown that N-, P- and S-deficiencies result in major reductions of root hydraulic conductivity (Lpr) which may lead to lowered stomatal conductance, but the relationship between the two conductance changes is not understood. In a variety of species, Lpr decreases in the early stages of NO3-, H2PO4(2-) and SO4(2-) deprivation. These effects can be reversed in 4-24 h after the deficient nutrient is re-supplied. Diurnal fluctuations of root Lpr have also been found in some species, and an example of this is given for Lotus japonicus. In nutrient-sufficient wheat plants, root Lpr is extremely sensitive to brief treatments with HgCl2; these effects are completely reversible when Hg is removed. The low values of Lpr in N- or P-deprived roots of wheat are not affected by Hg treatments. The properties of plasma membrane (PM) vesicles from wheat roots are also affected by NO3(-)-deprivation of the intact plants. The osmotic permeability of vesicles from N-deprived roots is much lower than that of roots adequately supplied with NO3-, and is insensitive to Hg treatment. In roots of L. japonicus, gene transcripts are found which have a strong homology to those encoding the PIP1 and PIP2 aquaporins of Arabidopsis. There is a very marked diurnal cycle in the abundance of mRNAs of aquaporin gene homologues in roots of L. japonicus. The maxima and minima appear to anticipate the diurnal fluctuations in Lpr by 2-4 h. The temporal similarity between the cycles of the abundance of the mRNAs and root Lpr is most striking. The aquaporin encoded by AtPIP1 is known to have its water permeation blocked by Hg binding. The lack of Hg-sensitivity in roots and PMs from N-deprived roots provides circumstantial evidence that lowered root Lpr may be due to a decrease in either the activity of water channels or their density in the PM. It is concluded that roots are capable, by means completely unknown, of monitoring the nutrient content of the solution in the root apoplasm and of initiating responses that anticipate by hours or days any metabolic disturbances caused by nutrient deficiencies. It is the incoming nutrient supply that is registered as deficient, not the plant's nutrient status. At some point, close to the initiation of these responses, changes in water channel activity may be involved, but the manner in which monitoring of nutrient stress is transduced into an hydraulic response is also unknown.
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Claims 13
Claim · model-written summary
N, P and S deficiencies reduced root hydraulic conductivity.
Not reportedTaxon
Verbatim
e1“N-, P- and S-deficiencies result in major reductions of root hydraulic conductivity (Lpr)”
Claim · model-written summary
Lpr decreased early during nitrate, phosphate and sulfate deprivation.
- Taxon
- variety of speciese1
- Treatment
- NO3-, H2PO4(2-) and SO4(2-) deprivatione1
- Outcome
- Lpre1
- Direction
- decreasese1
Not reportedComparator
Verbatim
e1“In a variety of species, Lpr decreases in the early stages of NO3-, H2PO4(2-) and SO4(2-) deprivation.”
Claim · model-written summary
Resupplying deficient nutrient reversed Lpr reduction within 4-24 h.
- Taxon
- variety of speciese2
- Treatment
- deficient nutrient is re-suppliede1
- Outcome
- Lpre2
- Direction
- reversede1
- Value
- 4-24 he1
Not reportedComparator
Verbatim
e1“These effects can be reversed in 4-24 h after the deficient nutrient is re-supplied.”
e2“In a variety of species, Lpr decreases in the early stages of NO3-, H2PO4(2-) and SO4(2-) deprivation.”
Claim · model-written summary
Lotus japonicus root Lpr showed diurnal fluctuations.
- Taxon
- Lotus japonicus
Lotus japonicuse1 - Outcome
- Diurnal fluctuations of root Lpre1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Diurnal fluctuations of root Lpr have also been found in some species, and an example of this is given for Lotus japonicus.”
Claim · model-written summary
Brief HgCl2 treatments affected root Lpr in nutrient-sufficient wheat, reversibly.
- Taxon
- wheat
Triticum aestivume1 - Treatment
- brief treatments with HgCl2e1
- Outcome
- root Lpre1
- Direction
- extremely sensitivee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In nutrient-sufficient wheat plants, root Lpr is extremely sensitive to brief treatments with HgCl2; these effects are completely reversible when Hg is removed.”
Claim · model-written summary
Hg did not affect low Lpr in N- or P-deprived wheat roots.
- Taxon
- wheatTriticum aestivume1
- Treatment
- Hg treatmentse1
- Outcome
- Lpre1
- Direction
- not affectede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The low values of Lpr in N- or P-deprived roots of wheat are not affected by Hg treatments.”
Claim · model-written summary
PM vesicles from nitrate-deprived wheat roots had lower osmotic permeability.
- Taxon
- wheatTriticum aestivume2
- Outcome
- osmotic permeability of vesiclese1
- Direction
- much lowere1
- Comparator
- roots adequately supplied with NO3-e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The osmotic permeability of vesicles from N-deprived roots is much lower than that of roots adequately supplied with NO3-”
e2“PM) vesicles from wheat roots”
Claim · model-written summary
Osmotic permeability of vesicles from N-deprived roots was insensitive to Hg.
- Taxon
- wheatTriticum aestivume2
- Treatment
- Hg treatmente1
- Outcome
- osmotic permeability of vesiclese1
- Direction
- insensitivee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The osmotic permeability of vesicles from N-deprived roots is much lower than that of roots adequately supplied with NO3-, and is insensitive to Hg treatment.”
e2“PM) vesicles from wheat roots”
Claim · model-written summary
Lotus japonicus roots contained transcripts homologous to Arabidopsis PIP1 and PIP2 aquaporins.
- Taxon
- L. japonicusLotus japonicuse1
- Gene
- PIP1 and PIP2 aquaporins of Arabidopsise1
- Outcome
- gene transcripts are found which have a strong homologye1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In roots of L. japonicus, gene transcripts are found which have a strong homology to those encoding the PIP1 and PIP2 aquaporins of Arabidopsis.”
Claim · model-written summary
Lotus root aquaporin homologue mRNAs showed a diurnal abundance cycle.
- Taxon
- L. japonicusLotus japonicuse1
- Gene
- aquaporin gene homologuese1
- Outcome
- diurnal cycle in the abundance of mRNAse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“There is a very marked diurnal cycle in the abundance of mRNAs of aquaporin gene homologues in roots of L. japonicus.”
Claim · model-written summary
Aquaporin mRNA peaks and troughs preceded Lpr fluctuations by 2-4 h.
- Taxon
- L. japonicusLotus japonicuse2
- Gene
- aquaporin gene homologuese2
- Outcome
- diurnal fluctuations in Lpre1
- Value
- 2-4 he1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The maxima and minima appear to anticipate the diurnal fluctuations in Lpr by 2-4 h.”
e2“abundance of mRNAs of aquaporin gene homologues in roots of L. japonicus.”
Claim · model-written summary
The authors suggest reduced water-channel activity or density explains low Lpr.
- Taxon
- wheatTriticum aestivume2
- Outcome
- lowered root Lpre1
- Qualifier
- decrease in either the activity of water channels or their density in the PMe1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The lack of Hg-sensitivity in roots and PMs from N-deprived roots provides circumstantial evidence that lowered root Lpr may be due to a decrease in either the activity of water channels or their density in the PM.”
e2“wheat roots”
Claim · model-written summary
The authors conclude roots monitor incoming nutrients and anticipate metabolic disturbances.
Verbatim
e1“roots are capable, by means completely unknown, of monitoring the nutrient content of the solution in the root apoplasm and of initiating responses that anticipate by hours or days any metabolic disturbances caused by nutrient deficiencies.”