Abstract
Water relations of growing segments of maize (Zea mays L.) coleoptiles were investigated with osmotic methods using either mannitol (MAN) or polyethylene glycol 6000 (PEG) as external osmotica. Segments were incubated in MAN or PEG solutions at 0 to - 15 bar water potential (Psi(o)) and the effects were compared on elongation growth, osmotic shrinkage, cell sap osmolality (OC), and osmotic pressure (pi(i)). The nonpenetrating osmoticum PEG affects pi(i) in agreement with Boyle-Mariotte's law, i.e. the segments behave in principle as ideal osmometers. There is no osmotic adjustment in the Psi(o) range permitting growth (0 to -5 bar) nor in the Psi(o) range inducing osmotic shrinkage (-5 to -10 bar). Promoting growth by auxin (IAA) has no effect on the osmotic behavior of the tissue toward PEG. In contrast to PEG, MAN produces an apparent increase in pi(i) accompanied by anomalous effects on segment elongation and shrinkage leading to a lower value for Psi(o) which establishes a growth rate of zero and to an apparent recovery from osmotic shrinkage after 2 hours of incubation. These effects can be quantitatively attributed to uptake of MAN into the tissue. MAN is taken up into the apoplastic space and the symplast as revealed by a large temperature-dependent component of MAN uptake. It is concluded that MAN, in contrast to PEG, is unsuitable as an extemal osmoticum for the quantitative determination of water relations of growing maize coleoptiles.
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Claims 10
Claim · model-written summary
PEG changed osmotic pressure according to Boyle Mariotte law.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The nonpenetrating osmoticum PEG affects pi(i) in agreement with Boyle-Mariotte's law”
t0“Maize”
Claim · model-written summary
No osmotic adjustment occurred across growth and shrinkage ranges.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There is no osmotic adjustment in the Psi(o) range permitting growth (0 to -5 bar) nor in the Psi(o) range inducing osmotic shrinkage (-5 to -10 bar).”
t0“Maize”
Claim · model-written summary
Auxin promoted growth but did not alter osmotic behavior toward PEG.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Promoting growth by auxin (IAA) has no effect on the osmotic behavior of the tissue toward PEG.”
t0“Maize”
Claim · model-written summary
Mannitol apparently increased osmotic pressure.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In contrast to PEG, MAN produces an apparent increase in pi(i)”
t0“Maize”
Claim · model-written summary
Mannitol produced anomalous elongation and shrinkage effects.
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“MAN produces an apparent increase in pi(i) accompanied by anomalous effects on segment elongation and shrinkage”
t0“Maize”
Claim · model-written summary
Mannitol lowered the water potential yielding zero growth.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leading to a lower value for Psi(o) which establishes a growth rate of zero”
t0“Maize”
e1“MAN produces an apparent increase in pi(i)”
Claim · model-written summary
Mannitol caused apparent shrinkage recovery after two hours.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an apparent recovery from osmotic shrinkage after 2 hours of incubation.”
t0“Maize”
e1“MAN produces an apparent increase in pi(i)”
Claim · model-written summary
Mannitol uptake explained the anomalous effects.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These effects can be quantitatively attributed to uptake of MAN into the tissue.”
t0“Maize”
Claim · model-written summary
Mannitol entered apoplast and symplast.
- Outcome
- MAN is taken up into the apoplastic space and the symplaste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“MAN is taken up into the apoplastic space and the symplast as revealed by a large temperature-dependent component of MAN uptake.”
t0“Maize”
Claim · model-written summary
Mannitol was unsuitable for quantitative water relations determination.
- Outcome
- unsuitable as an extemal osmoticum for the quantitative determination of water relationse0
- Comparator
- PEGe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“MAN, in contrast to PEG, is unsuitable as an extemal osmoticum for the quantitative determination of water relations of growing maize coleoptiles.”
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