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4) Biodiversity, evolution and disease
12) Communicable diseases
12.4 Plant defences against pathogens
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Cards (7)
primary defences in plants:
waxy
cuticle
bark
of tree trunks
cellulose
cell walls
Attack - 1
some
molecules
from the
pathogen
are recognised directly by the
plant cell
breakdown products
of the
cellulose cell wall
are also directly recognised by the
plant cell
receptors
on the
plasma membrane
are the
mediators
of this response
Attack -
2
signal travels to the
nucleus
and new
gene expression
is initiated
this leads to the
synthesis
of new
defence proteins
the newly made
defensive
molecules attack the
pathogen
physical defences:
polysaccharides
are made which enhance the
strength
of the
cell wall
callose
lignin
defensive chemicals
signal alarm to other cells before they are also
attacked
production of
callose
:
when a
pathogen
is
detected
the
plant cells
rapidly produce
high
levels of
callose
callose
is a
polysaccharide
, made of
beta glucose monomers
role of
callose
:
deposited
between the
cell walls
and
cell membranes
next to the
infected cells
- this
prevents
further
spread
lignin
is added to to the
callose
to
strengthen
the
barrier
callose
also blocks
sieve plates
in the
phloem
callose
is also
deposited
in the
plasmodesmata
of
connecting cells
Chemical defences:
anti-fungal compounds
- e.g
caffeine
(toxic to fungi and insects) e.g
chitinase
(enzyme that breaks down fungal cell walls)
Insecticides
Insect repellents
e.g citronella
anti-oomycetes
e.g glucanase (break down glucans which are found in cell walls)