The Cell Cycle

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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

Three Major Pathways of Transport

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