Abstract
The vacuolar and cytoplasmic inorganic phosphate (Pi) content of the mature regions of maize roots was measured by a 31P NMR technique which used an external standard to avoid the need for tissue extraction and which exploited the relatively rapid relaxation of cytoplasmic Pi in order to improve the detection of this pool in fully-vacuolated cells. In mature roots of maize growing with abundant external phosphate, the concentration of Pi in the cytoplasm was approximately 6.5 mol m−3. When these plants were deprived of external phosphate, the vacuolar Pi content of the roots decreased rapidly, but the cytoplasmic Pi concentration initially remained constant and did not begin to decline until P-stress became severe. Calculations show that withdrawal of Pi from the vacuoles into the cytoplasm under these conditions would be against an electrochemical gradient. During P-starvation, an increased capacity for Pi influx developed, preceding any detectable change in the cytoplasmic Pi content of the roots. This response is considered in terms of parallel effects on transport sites for phosphate at the plasmalemma and at the tonoplast. Comparisons of simultaneous rates of influx and net uptake implied that phosphate efflux accounted for < 10% of influx in plants of a steady or declining P-status. However, direct measurements of efflux suggested that this process may be temporarily accelerated when plants are recovering from P-stress.
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Claims 8
Claim · model-written summary
Cytoplasmic phosphate concentration in mature roots with abundant external phosphate was approximately 6.5 mol m−3.
- Organ / stage
- mature rootse0
- Outcome
- concentration of Pi in the cytoplasme0
- Value
- approximately 6.5 mol m−3e0
- Qualifier
- abundant external phosphatee0
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In mature roots of maize growing with abundant external phosphate, the concentration of Pi in the cytoplasm was approximately 6.5 mol m−3.”
Claim · model-written summary
External phosphate deprivation rapidly decreased vacuolar root phosphate content.
- Treatment
- deprived of external phosphatee0
- Outcome
- vacuolar Pi content of the rootse0
- Direction
- decreased rapidlye0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When these plants were deprived of external phosphate, the vacuolar Pi content of the roots decreased rapidly”
t0“Maize Roots”
Claim · model-written summary
During initial phosphate deprivation, cytoplasmic phosphate concentration remained constant.
- Treatment
- deprived of external phosphatee1
- Outcome
- cytoplasmic Pi concentratione0
- Direction
- remained constante0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the cytoplasmic Pi concentration initially remained constant”
t0“Maize Roots”
e1“deprived of external phosphate”
Claim · model-written summary
Cytoplasmic phosphate concentration declined only once phosphorus stress became severe.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“did not begin to decline until P-stress became severe”
t0“Maize Roots”
e1“cytoplasmic Pi concentration”
Claim · model-written summary
Calculated vacuole to cytoplasm phosphate transfer would oppose an electrochemical gradient during deprivation.
- Outcome
- withdrawal of Pi from the vacuoles into the cytoplasme0
- Qualifier
- against an electrochemical gradiente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Calculations show that withdrawal of Pi from the vacuoles into the cytoplasm under these conditions would be against an electrochemical gradient.”
t0“Maize Roots”
Claim · model-written summary
Phosphate starvation increased capacity for Pi influx before cytoplasmic Pi changed.
- Treatment
- P-starvatione0
- Outcome
- capacity for Pi influxe0
- Direction
- increasede0
- Qualifier
- preceding any detectable change in the cytoplasmic Pi content of the rootse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“During P-starvation, an increased capacity for Pi influx developed, preceding any detectable change in the cytoplasmic Pi content of the roots.”
t0“Maize Roots”
Claim · model-written summary
Phosphate efflux was less than 10% of influx in plants with steady or declining phosphorus status.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“phosphate efflux accounted for < 10% of influx in plants of a steady or declining P-status.”
t0“Maize Roots”
Claim · model-written summary
Direct measurements suggested efflux may accelerate temporarily during recovery from phosphorus stress.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“direct measurements of efflux suggested that this process may be temporarily accelerated when plants are recovering from P-stress.”
t0“Maize Roots”
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