1. 1.6 Exocytosis and Endocytosis

2. Exocytosis: - from TGN to PM,
- proteins, lipids, polysaccharides, glycoproteins,
proteoglycans

4. Endocytosis: - retrives excess membrane for recycling
through the formation of PM membrane infolding.
turn over PM and cell wall molecules
remove activated receptors from the cell surface
In animals, plays major role in the uptake of nutrients
but little evidence suggests such a role in plants

5. In plants , turgor pressure affects membrane events associated
with exocytosis and membrane recycling.

6. Fig 1-29. Cross section images
of secretory vesicles.

7. 2) Turgor pressure also affects endocytosis and membrane recycling

9. 3) The membrane compartments associated with endocytosis can be
identified by following the uptake of tracer molecules.
Clathrin-coated vesicles budding from a PM
higher magnification TEM of clathrin-coated vesicles.

10. The endocytic pathway Plasma membrane/extracellular space
Clathrin-coated pits and vesicles
Non-coated vesicles
Partially coated reticulum (likely extention of the TGN)
Multivesicular bodies, organelles (not to be destined for degradation)
Vacuoles

11. Multivesicular body in the cytoplasm of a tobacco cell

12. 1.7. Vacuoles
Fluid filled compartments encompassed by a membrane, called the tonoplast
Conspicuous organelles of most plant cells
Numerous small vacuoles in apical meristem cells
combine into one or a few larger vacuoles as the cell matures and expands
Root meristem cell
Mesophyll leaf cell

13. View of spongy mesophyll cells in a bean leaf

14. Vacuoles store a large variety of molecules
: inorganic ions, organic acids, sugars, enzymes, store proteins
and many types of secondary metabolites.
solutes -> water -> turgor pressure -> cell enlargement
Many hydrolytic enzymes found in vacuoles,
suggesting a role in turnover of cellular constituents
(like lysosomes in animal cells)
Many hydrolytic enzymes results in HR-like cell death
in response to pathogen

15. 1) Plants use vacuoles to produce large cells cheaply
- To maintain the turgor pressure of, solutes must be actively transported
into the growing vacuole.
Electrochemical gradient is produced by two proton pumps
(V-type H+-ATPase and H+-pyrophosphatase (H+-PPase)
The movements of water across the tonoplast
is mediated by aquarin channels

16. 2) Plant vacuoles are multifunctional compartments
a. Storage: inorganic ions, organic acids, sugars, enzymes, store proteins
and many types of secondary metabolites
b. Digestion: acid hydrolases (protease, nuclease, glycosidase, and lipases)
are found in.  recycling (turnover and retrieval of nutrients)
c. pH and ionic homeostasis: reseiviers of protons and ions (calcium)
 regulates cytosolic pH, the activity of enzymes,
the assembly of cytoskeletal structures and membrane fusion
d. Defense against microbial pathogens and hebivores:
- phenolic compounds, alkaloids, cyanogenic glycosides
and protease inhibitor to insect and herbivores
- cell degrading enzymes;chitinase and glucanase, defense molecules
to fungi and bacteria
- latexes, to insect and fungi herbivores

17. e. Sequstration of toxic compounds:
heavy metals
toxic metabolites (oxalate)
f. Pigmentation:
antocyanin pigments
– attract pollinator and seed dispersers
- screen out UV and visible light preventing photooxidative damage

18. 3) Many plant cells contains two different vacuole systems
Neutral protein vacuoles
(V1)
b. Acidic, lytic vacuoles
(V2)

19. 4) Vacuoles may be the only membrane compartments
that can be created de novo
provacuoles arise from ER domain
 in which H+-ATPases, a-TIP and stoage proteins accumulate
 After their separation from ER, provacuoles inflate
 they become full-fledged vacuoles
2) the central vacuole appears to arise from smooth ER tubes
 these tubes assemble in to a cage-like structure
 cleared of organells
 then autophagocytosed into the forming vacuole
or displaced as the vacuole tube fuse and inflate.

20. 1.8 The nucleus Contains most of the cell’s genetic information
Serves as the center of regulatory activity