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Dormancy Metabolism Characteristics
1.
Minimal metabolic turnover
2.
Low water content
3.
General lack of cytoplasmic movement
4.
Temperature optima for germination
which are often very different than those
for vegetative growth
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Factors
that influence spore dormancy
I.
Internal factors
a.
Maturity
b.
Longevity
c.
Vitality
d.
Endogenous substrate reserves
II.
External factors
a.
Temperature
b.
Light
c.
Hydration
d.
Aeration
e.
Chemical environment
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Definitions
a.
Maturity = whether or not spore is
fully developed
b.
Longevity = how long (max) a spore
can live
c.
Vitality = maximum germination
capacity
d.
Endogenous substrates:
substrates that nourish spores during
dormancy
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Definitions
1.
Dormancy - any rest period or
reversible interruption of the growth or
development of the fungus
2.
Constitutional dormancy - germination
is delayed by an innate property of the
spore*
3.
Exogenous dormancy - development is
delayed only because of one or more
unfavorable chemical or physical conditions
of the environment**
*a)
Barriers to nutrient or water
penetration
b)
Some internal metabolic block
c)
The production of a germination
inhibitor
d)
Loss of a germination promoter
**
dessication, absence of light, substrate
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Other
terms relating to spore dormancy
1.
Activation - the application of an
environmental or chemical stimulus to the
spore (constitutionally dormant) to induce
germination.
2.
Maturation - the complex changes that
must occur during spore development to
produce a spore capable of dormancy and
germination.
3.
After-ripening - the treatments which
a fungal spore must undergo in nature before
it may germinate.
4.
Germination - the resumption in the
spore of normal metabolic processes that
usually lead to the production of one or
more germ tubes or buds.
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Germination Events
1.
Reduction of refractive index
(probably due mainly to H2O
uptake)
2.
Isotropic (nonpolar) growth of spore
(probably due to both stretching of existing
wall and some new wall synthesis
3.
Formation of a new cell wall inside
of old cell wall
4.
Polar formation of new bud or germ
tube (wall of new bud or germ tube usually
formed by extension of new inner wall of
spore)
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Documented
Components* of Protein Synthesizing
Apparatus in Spores
1.
Ribosomes**
2.
tRNA
3.
aminoacyl tRNA synthetase
4.
Transfer enzymes
5.
Elongation factors
6.
etc.
*all
components seem to be active when assayed in
vitro.
**only
a few types of spores have been found to
have polyribosomes in dormant situation.
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Evidence that Protein Synthesis is Essential for
Germination
1.
Conidia and ascospore germination of N.
crassa inhibited by cycloheximide (also
many other spores)
2.
Conidia of ts mutants for protein
synthesis of N.
crassa will not form germ tubes (also
many other species)
3.
Conidia of some amino acid auxotrophs
of N.
crassa & other fungi will not
germinate in unsupplemented media
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Germination
Categories of Spores
Group
I = spores of most fungi in which the
synthesis of RNA & protein appear to
begin together, a short time after
placement
in germination medium
Group
II* = protein synthesis precedes RNA
synthesis (preformed message & polysomes)
Group
III** = RNA synthesis precedes protein
synthesis
*only
a few examples
**very
rare and not well documented
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