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Questions
1. What is driving force for
apical extension
- Not known but probably
partly turgor pressure
- Tips have high osmotic
pressure
- Tips blow out in dilute
acids
2. Evidence for tip growth of
molds?
Burgeffs experiment
~ 1900
etc.
3.
How is wall synthesized to -> tip or bud
growth?
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Evidence for in situ synthesis of cell wall microfibrils
a.
Cell fractionation studies - sugar
nucleotide transferases for synthesis of b
glucans & chitin present in plasma
membrane
b.
Chitin synthase in Zygomycota has
been demonstrated to be localized in hyphal
tips
c.
Zoospores prior to encystment have no
demonstrable preformed micro-fibrils in
their cytoplasm
d.
EM tends to demonstrate that wall
microfibrils are not carried to wall
synthetic loci in apical vesicles.*
* Vesicles seem to be
transporters of amorphores matrix materials.
Heteropolysaccharides
Mannoproteins
etc.
190a
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Evidence for in situ synthesis of cell wall microfibrils (cont)
e.
Demonstration that at least some, if
not all chitin is synthesized, most likely,
in a vectorial way as demonstrated by
unilateral formation of chitin by isolated
plasma membrane.
Pretreatment of
protoplasts with gluteradehyde before lysis
--> no effecting chitin synthesis
Pretreatment of
disrupted membranes with gluteraldehyde
inhibited vectorial synthesis
190c
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Indirect
evidence for a role for hydrolytic enzymes
in wall synthesis
a.
Wall hydrolytic enzymes can be
isolated from hyphal tips and yeast buds
b.
Is a positive correlation between
concentration of hydrolytic enzymes and
rates of tip extension and hyphal branching
c.
Fungal hyphae have intrinsic ability
to execute carefully controlled dissolution
of own wall.
e.g. - clamps, anastomosis, bud
emergence, branch formation
d.
Hyphal tips highly susceptible to
disruption, e.g., tips blow out in dilute
acid solutions
193
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Possible
implications
1.
Fungal cell wall synthesis depends on
a gradient of cell wall synthesis
accompanying a gradient of cell wall lysis.
2.
For this to occur lytic and synthetic
components and machinery must be
compartmentalized.
How?
Vesicles??
194
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