Vacuole
Considered “outside” of the cytoplasm.
1.
Structure? The only “structure” concerns the tonoplast—vacuole
membrane. Single bilayer of 10 nM thick and resembles plasma
membrane. What are the differences between the two
membranes?
Most of plant cells have
Large central vacuole.
Bean mesophyll cells
With chloroplasts and
The central vacuole
2. Formation and development
2
. This is the only organelle that is produced de novo (not through
Dinheritance). What is the origin of vacuole?
eIt is has been difficult to determine because many vesicular
compartments in the cell are similar to precursors of vacuole—
vprovacuoles. Most likely the transGolgi network (TGN) and smooth
eER produce provacuole that develop into mature vacuole.
l
oTEM and molecular marker labeling.
p
In the meristem cells, only very small vacuoles or provacuoles exist.
mAs the cell expands, small vacuoles fuse to form larger vacuoles and
eeventually form the central vacuole. AS the cells differentiate into
ndifferent types, the vacuole develops into various functional groups as
t well. Like the plastid development---depending on the cell type…
a
n
d
3. Function of vacuole
1) As lysosome in animal cells: containing a number of lytic enzymes
that can digest he whole cell. Example, xylem vessel formation.
Autolysis.
2) Garbage disposal and storage space:
a) chemical weapons and medicines: secondary toxic products
for self defense purposes and some of them are medicines.
examples: nicotine, caffeine, taxol, opium, …
Antipoisoning
Theriak: opium,
snake, and wine
b) pigments for coloration: pollination/seed disbursal.
c) toxic chemicals accidentally “swallowed”: agrochemicals etc
d) storage proteins: seed storage—cotyleadons/endosperms
The bigger vacuoles are
protein storage and the
small ones are lytic
vacuoles—in single
type of cells (aleurone
cell from a barley
seed).
3) Homeostatic balancer and osmotic regulation:
Vacuole is less important space in terms of life reactions…
a) Salt balance:K+ as example
K+ uptake into
cytoplasm and
then into
vacuole.
Depending on
the need in the
cytoplasm
(priority), K+
distribution is
in constant
flux.
On the other hand, for toxic Na+, vacuole serve as a
detoxifying space--H+-Na+ antiporter
Found in yeast and
plants.
Overexpression of
this antiporter confer
plant tolerance to
high salt in the soil.
Na+
Na+
Na+ Na+
H+
Na+
Na+
H+
A big family of H-Na antiporters also exist in the
plasma membrane and help remove Na from the
cytoplasm. Overexpression of these can also make
plants more tolerant to saline soil.
b) PH balancer or buffer
AS mentioned earlier, the H-ATPases in the PM and tonoplast both work to
pump out the H+ produced in the cytoplasm that has a rather stable pH
around 7. The vacuole pH can be as acidic as 4-5.
c) Osmotic regulation—arguably the most important function for most of
plant cells
Turgor pressure---due to the osmotic gradient between outside and inside of
the cell and the limited flexibility of cell wall.
Osmotic gradient---Cytoplasm and vacuole—which component is more
important? How is this gradient formed?
Transport/membranes/water/ions/sugar/organic acids (solutes).
Think about how cell wall, membranes, vacuoles, etc work together to make
a cell expand…This is related to both cell growth and
What is Gas exchange?
Why important?
How is it regulated?
Stomata and guard
Cells.
PM and tonoplast
Channels and carriers
Turgors and movements
Signals and response
Light and dark,
water/drought
Stress, Survival vs
productivity