Addition of Solutes reduces water potential.
Slide 22
Water relations in plant cells
ψP = 0 ψS = −0.7
ψP = 0 ψS = −0.9
ψP = 0 ψS = −0.7
ψP = 0 ψS = 0
ψ = −0.9 MPa
ψ = −0.7 MPa
ψ = 0 MPa
ψ = 0 MPa
(a) Initial conditions: cellular ψ > environmental ψ
(b) Initial conditions: cellular ψ < environmental ψ
0.4 M sucrose solution:
Plasmolyzed cell
Initial flaccid cell:
Pure water:
Turgid cell
ψP = 0 ψS = −0.9
ψ = −0.9 MPa
Slide 23
Turgor loss in plants causes wilting, which can be reversed when the plant is watered.
Aquaporins are transport proteins in the cell membrane that allow the passage of water.
The rate of water movement is likely regulated by phosphorylation of the aquaporin proteins.
Slide 24
A wilted Impatiens plant regains its turgor when watered
Cells in wilted plant to the left - plasmolysis
Cells in plant below - turgor.
Slide 25
Transport is also regulated by the compartmental structure of plant cells.
The plasma membrane directly controls the traffic of molecules into and out of the protoplast.
The plasma membrane is a barrier between two major compartments, the cell wall and the cytosol.
Slide 26
The third major compartment in most mature plant cells is the central vacuole, a large organelle that occupies as much as 90% or more of the protoplast’s volume.
The vacuolar membrane = tonoplast - regulates transport between the cytosol and the vacuole.
Slide 27
In most plant tissues, the cell wall and cytosol are continuous from cell to cell.
The cytoplasmic continuum is called the symplast.
The cytoplasm of neighboring cells is connected by channels = plasmodesmata.
The apoplast is the continuum of cell walls and extracellular spaces.
Slide 28
Short Distance Transport
Cell wall
Cytosol
Vacuole
Plasmodesma
Vacuolar membrane
Plasma membrane
(a) Cell compartments
Key
Transmembrane route
Apoplast
Symplast
Apoplast
Symplast
Apoplast
Symplastic route
Apoplastic route
(b) Transport routes between cells
Slide 29