Abstract
Growing pea stem tissue, when isolated from an external supply of water, undergoes stress relaxation because of continued loosening of the cell wall. A theoretical analysis is presented to show that such stress relaxation should result in an exponential decrease in turgor pressure down to the yield threshold (Y), with a rate constant given by phi epsilon where phi is the metabolically maintained irreversible extensibility of the cell wall and epsilon is the volumetric elastic modulus of the cell. Stress relaxation was measured in pea (Pisum sativus L.) stem segments using the pressure microprobe technique. From the rate of stress relaxation, phi of segments pretreated with water was calculated to be 0.08 per megapascal per hour while that of auxin-pretreated tissue was 0.24 per megapascal per hour. These values agreed closely with estimates of phi made by a steady-state technique. The yield threshold (0.29 megapascal) was not affected by auxin. A theoretical analysis is also presented to show that the tissue hydraulic conductance may be estimated from the T/sub 1/2/ of tissue swelling. Experimentally, pea stems had a swelling T/sub 1/2/ of 2.0 minutes, corresponding to a relative hydraulic conductance of about 2.0 per megapascal per hour. This value ismore » at least 8 times larger than phi. From these data and from computer modeling, it appears that the radial gradient in water potential which sustains water uptake in growing pea segments is small (0.04 megapascal). This means that hydraulic conductance does not substantially restrict growth. The results also demonstrate that the stimulation of growth by auxin can be entirely accounted for by the change in phi.« less
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Claims 8
Claim · model-written summary
Pea stem tissue isolated from external water undergoes stress relaxation through wall loosening.
- Taxon
- pea
Lathyrus oleraceuse0 - Outcome
- stress relaxatione0
- Qualifier
- continued loosening of the cell walle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Growing pea stem tissue, when isolated from an external supply of water, undergoes stress relaxation because of continued loosening of the cell wall.”
Claim · model-written summary
Water-pretreated segments had phi of 0.08 per megapascal per hour.
- Taxon
- peaLathyrus oleraceuse1
- Treatment
- pretreated with watere0
- Outcome
- phie0
- Value
- 0.08 per megapascal per houre0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“phi of segments pretreated with water was calculated to be 0.08 per megapascal per hour”
e1“pea (Pisum sativus L.)”
Claim · model-written summary
Auxin-pretreated segments had phi of 0.24 per megapascal per hour.
- Taxon
- peaLathyrus oleraceuse2
- Treatment
- auxin-pretreated tissuee0
- Outcome
- phie1
- Value
- 0.24 per megapascal per houre0
- Comparator
- pretreated with watere1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“that of auxin-pretreated tissue was 0.24 per megapascal per hour”
e1“phi of segments pretreated with water was calculated to be 0.08 per megapascal per hour”
e2“pea (Pisum sativus L.)”
Claim · model-written summary
Auxin did not affect the yield threshold of 0.29 megapascal.
- Taxon
- peaLathyrus oleraceuse1
- Treatment
- auxine0
- Outcome
- yield thresholde0
- Direction
- not affectede0
- Value
- 0.29 megapascale0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The yield threshold (0.29 megapascal) was not affected by auxin.”
e1“pea (Pisum sativus L.)”
Claim · model-written summary
Pea stem swelling half-time was 2.0 minutes.
- Taxon
- peaLathyrus oleraceuse0
- Outcome
- swelling T/sub 1/2/e0
- Value
- 2.0 minutese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“pea stems had a swelling T/sub 1/2/ of 2.0 minutes”
Claim · model-written summary
Relative hydraulic conductance was about 2.0 per megapascal per hour.
- Taxon
- peaLathyrus oleraceuse1
- Outcome
- relative hydraulic conductancee0
- Value
- about 2.0 per megapascal per houre0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“corresponding to a relative hydraulic conductance of about 2.0 per megapascal per hour”
e1“pea stems”
Claim · model-written summary
The modeled radial water-potential gradient in growing pea segments was small, 0.04 megapascal.
- Taxon
- peaLathyrus oleraceuse0
- Outcome
- radial gradient in water potentiale0
- Value
- 0.04 megapascale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the radial gradient in water potential which sustains water uptake in growing pea segments is small (0.04 megapascal)”
Claim · model-written summary
Hydraulic conductance was interpreted as not substantially restricting growth.
- Taxon
- peaLathyrus oleraceuse1
- Outcome
- growthe0
- Qualifier
- hydraulic conductancee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“hydraulic conductance does not substantially restrict growth”
e1“pea segments”
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