Download Vacuole metabolites

VACUOLE
Vacuole
Vacuole
The name derives from the latin ‘vaccuum’ (empty space).
Region of the plant cell delimited by a single membrane (tonoplast). The latter is
mainly involved in regulating the movements of ions around the cell, and in isolating
materials that might be harmful or a threat to the cell itself.
It is something like a sac filled with water containing inorganic and organic
molecules.
It acts as a storage organ.
Vacuole originates from a space of endoplasmic reticulum; tonoplast derives from
fusions of Golgi body vesicles .
Small and numerous vacuoles in a young cell; during cell growth they increase in size
and merge each other into a single vacuole.
Replacing the role of lysosomes, vacuole is involved in autophagy and degradation of
molecules and organelles (e.g. inactive mitochondria and plastids).
In an adult cell, it can occupy 80-90% of the total cell volume.
Vacuole
•The main role of the central vacuole is to maintain turgor pressure against the cell wall.
Proteins found in the tonoplast (aquaporins) control the flow of water into and out of the
vacuole through active transport, pumping potassium (K+) ions into and out of the vacuolar
interior. Due to osmosis, water will diffuse into the vacuole, placing pressure on the cell wall. If
water loss leads to a significant decline in turgor pressure, the cell will plasmolyze.
•Turgor pressure exerted by vacuoles is also required for cellular elongation: as the cell wall is
partially degraded by the action of expansins, the less rigid wall is expanded by the pressure
coming from within the vacuole. Turgor pressure exerted by the vacuole is also essential in
supporting plants in an upright position.
•Another function of a central vacuole is that it pushes all contents of the cell’s cytoplasm
against the cellular membrane, and thus keeps the chloroplasts closer to light.
Vacuole metabolites
•Most plants store chemicals through active
transport in the vacuole.
•The fluid contained in the vacuole is a water
solution with pH values of 4-5 favouring the
activity of hydrolytic enzymes in the cytosol.
•If the cell is broken, for example by a
herbivore, then the two chemicals can react
forming toxic chemicals (e.g. in garlic, alliin
and the enzyme alliinase are normally
separated but form allicin if the vacuole is
broken) useful for defensive purposes.
Vacuole metabolites
The main constituent is H2O together with:
ions : Ca++, K+, Cl-, Na+, HPO4sugar
organic acids and their salts: Ca oxalate
enzymes
proteins (aleurone grains)
PRIMARY METABOLITES
•These molecules are not synthesized into the vacuole, but in cytoplasm
and then they are stored in vacuole.
•The pharmaceutical importance of vacuole derives from the presence
of a large number of bioactive molecules, well-known as SECONDARY
METABOLITES.