Abstract
Net accumulation of Cl− by intact barley plants was virtually eliminated in roots and reduced by 40% in shoots when external media (0.5 mol m−3 CaSO4 plus 0–5 mol m−3 KCI) were supplemented with 0.25 mol m− Ca(NO3)2. Plasmalemma 36Cl− influx (Φoc) was shown to be insensitive to external NO3- in plants which had previously been grown in solutions lacking −3, but Φoc became sensitive to NO3-after a lag period of 3–6 h. Kinetic analyses revealed that the inhibition of 36C1− influx by external NO3- was complex. At 0.25 mol m−3 NO3- the Vmax for Cl− influx was reduced by greater than 50%, with insignificant effects upon Km. At 0.5 mol m−3 NO3- there was no further effect upon Vmax but Km for influx increased from 38±5 mmol m−3 to 116±26 mmol m−3. By contrast, Cl− efflux was found to be insensitive to external NO3-. A model for the regulation of Cl− influx is proposed which involves both negative feedback effects from vacuolar NO3- +Cl−) concentration and (external) NO3- inhibition of Cl− influx at the plasmalemma. These combined effects serve to discriminate against Cl− accumulation, favouring NO3- accumulation, when the latter ion is available. Such observations are inconsistent with recent proposals for the existence of bona fide homeostats for chloride accumulation in higher plants.
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Claims 12
Claim · model-written summary
Net Cl- accumulation in barley roots was virtually eliminated when external media were supplemented with Ca(NO3)2.
- Taxon
- barley
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Hordeum vulgaree0 - Organ / stage
- rootse0
- Treatment
- supplemented with 0.25 mol m− Ca(NO3)2e0
- Outcome
- Net accumulation of Cl−e0
- Direction
- virtually eliminatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“Net accumulation of Cl− by intact barley plants was virtually eliminated in roots and reduced by 40% in shoots when external media (0.5 mol m−3 CaSO4 plus 0–5 mol m−3 KCI) were supplemented with 0.25 mol m− Ca(NO3)2”
Claim · model-written summary
Net Cl- accumulation in barley shoots was reduced by 40% when external media were supplemented with Ca(NO3)2.
- Taxon
- barleyHordeum vulgaree0
- Organ / stage
- shootse0
- Treatment
- supplemented with 0.25 mol m− Ca(NO3)2e0
- Outcome
- Net accumulation of Cl−e0
- Direction
- reducede0
- Value
- 40%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Net accumulation of Cl− by intact barley plants was virtually eliminated in roots and reduced by 40% in shoots when external media (0.5 mol m−3 CaSO4 plus 0–5 mol m−3 KCI) were supplemented with 0.25 mol m− Ca(NO3)2”
Claim · model-written summary
Plasmalemma 36Cl- influx was insensitive to external NO3- in plants previously grown in solutions lacking nitrate.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- external NO3-e1
- Outcome
- Plasmalemma 36Cl− influxe1
- Direction
- insensitivee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“Plasmalemma 36Cl− influx (Φoc) was shown to be insensitive to external NO3- in plants which had previously been grown in solutions lacking −3”
Claim · model-written summary
Plasmalemma 36Cl- influx became sensitive to NO3- after a lag period of 3-6 h.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“Φoc became sensitive to NO3-after a lag period of 3–6 h”
Claim · model-written summary
At 0.25 mol m-3 NO3- the Vmax for Cl- influx was reduced by more than 50%.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- 0.25 mol m−3 NO3-e1
- Outcome
- Vmax for Cl− influxe1
- Direction
- reducede1
- Value
- greater than 50%e1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“At 0.25 mol m−3 NO3- the Vmax for Cl− influx was reduced by greater than 50%, with insignificant effects upon Km”
Claim · model-written summary
At 0.25 mol m-3 NO3- the Km for Cl- influx was insignificantly affected.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- 0.25 mol m−3 NO3-e1
- Outcome
- Kme1
- Direction
- insignificant effectse1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“At 0.25 mol m−3 NO3- the Vmax for Cl− influx was reduced by greater than 50%, with insignificant effects upon Km”
Claim · model-written summary
At 0.5 mol m-3 NO3- there was no further effect on Vmax.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- 0.5 mol m−3 NO3-e1
- Outcome
- Vmaxe1
- Direction
- no further effecte1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“At 0.5 mol m−3 NO3- there was no further effect upon Vmax but Km for influx increased from 38±5 mmol m−3 to 116±26 mmol m−3”
Claim · model-written summary
At 0.5 mol m-3 NO3- the Km for Cl- influx increased from 38±5 to 116±26 mmol m-3.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- 0.5 mol m−3 NO3-e1
- Outcome
- Km for influxe1
- Direction
- increasede1
- Value
- 38±5 mmol m−3 to 116±26 mmol m−3e1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“At 0.5 mol m−3 NO3- there was no further effect upon Vmax but Km for influx increased from 38±5 mmol m−3 to 116±26 mmol m−3”
Claim · model-written summary
Cl- efflux was insensitive to external NO3-.
- Taxon
- barleyHordeum vulgaree0
- Treatment
- external NO3-e1
- Outcome
- Cl− effluxe1
- Direction
- insensitivee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“Cl− efflux was found to be insensitive to external NO3-”
Claim · model-written summary
A model is proposed in which Cl- influx is regulated by negative feedback from vacuolar NO3- plus Cl- concentration and by external NO3- inhibition at the plasmalemma.
- Taxon
- barleyHordeum vulgaree0
- Outcome
- regulation of Cl− influxe1
- Qualifier
- negative feedback effects from vacuolar NO3- +Cl−) concentratione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“A model for the regulation of Cl− influx is proposed which involves both negative feedback effects from vacuolar NO3- +Cl−) concentration and (external) NO3- inhibition of Cl− influx at the plasmalemma”
Claim · model-written summary
The combined effects discriminate against Cl- accumulation, favouring NO3- accumulation when nitrate is available.
- Taxon
- barleyHordeum vulgaree0
- Compound
- NO3-e1
- Outcome
- Cl− accumulatione1
- Qualifier
- discriminate againste1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intact barley plants”
e1“These combined effects serve to discriminate against Cl− accumulation, favouring NO3- accumulation”
Claim · model-written summary
The observations are inconsistent with proposals for bona fide homeostats for chloride accumulation in higher plants.
- Taxon
- higher plantsEmbryophytae0
- Outcome
- inconsistent with recent proposals for the existence of bona fide homeostats for chloride accumulatione0
Verbatim
e0“Such observations are inconsistent with recent proposals for the existence of bona fide homeostats for chloride accumulation in higher plants”