the enzymes study in plant diseases for benificial
1. ENZYMES IN PLANT DISEASES
• Enzymes are large protein molecules that
catalyse all the interrelated reactions in a
living cell
• Some enzymes are constitutive.
• Many are produced only when they are
needed by the cell in response to internal
or external gene activators (induced)
• Anton de Bary reported the role of enzymes
and toxins in tissue disintegration caused
by Sclerotinia sclerotiorum
3. • Cutinases, cellulases, pectinases and
lignases are often secreted by the
pathogenic organism.
• Fungi, nematodes and bacteria are all
known to produce one or more of the
above
• Enzymes in specific pathogen-
host combinations.
• Viruses and viroids - no secretion
4. Enzymes degrade cuticular
wax
• In the cuticle of
many aerial plant
parts
• Some fungi produce
enzymes that
degrade waxes
• Eg: Puccinia hordei
5. Enzymes degrade cutin
• Cutin- main component
of cuticle
• Many fungi and bacteria
produce cutinase-
• Fungi constantly
produce cutinase in
small amount
• come in contact with
cutin release small
amount of monomers
• enter the pathogen cell
and trigger expression of
cutinase gene
6. • Presence of glucose suppresses the
expression of cutinase gene
• Enzymes reaches the higher concentration at
penetration point of germtube and infection
peg of appressorium forming fungi
7. • Pathogens produce higher amount of
cutinase seems to be more pathogenic
than others
• Cutinase inhibitors or antibodies
applied to plant surface protect plants
from fungal pathogens
• Eg: Fusarium
Penicillium
spinulosum (rotting
of leaves)
8. Pectic substances
• Main component of middle lamella-
intracellular cement
• Pectin-polysaccharides with side chains
• Enzyme degrade pectic substances are
PECTINASES or PECTOLYTIC ENZYMES
• Examples
– Pectin methyl esterases- remove small branches of
pectic chains and promote the attack of chain
splitting pectinases
– Polygalacturonases – split the pectic chain by
adding a molecule of water
– Pectin lyases – split the chain by removing a
molecule of water
9.
10. • Pectinase: 2 types
– Endopectinase : break pectin chains at
random sites
– Exopectinase :only break terminal linkage
• Pathogen produce a small amount of
pectin all the time
• When contact with the pectin in the host
they produce small amount of
monomers,dimers or oligomers
• These induce the pectinase
production in large amount
11. • Pectin degradation produce many
diseases particularly soft rotting of
tissues
• Pectic enzymes are produced by
germinating spores and act
together with other pathogen
enzymes – helps in penetration of
host
• Pectin degradation results in
liquefaction of pectic substances
that hold plant cells together- lead
to weakening of cell wall – leads to
tissue maceration
12. • Weakening of plant tissue and
maceration lead to inter and intra
cellular invasion of tissue by pathogen
• Eg
– Brown rot (Monilinia fructicola) in plum
– Bacterium Erwinia sp.
– Psudomonas
14. • Soluble sugars serve as the food for
pathogens
• Cellulases produced by several
phytopathogenic fungi, bacteria,
nematodes and parasitic higher plants
• Softening and disintegration of cell wall
• Liberating large molecules to transpiration
stream which interfere with normal
movement of water
• eg:
– Corn stalk rot fungus Fusarium
– Rhizoctonia solani
– Fusarium moniliforme
– Sclerotium rolfsii
15. Hemicelluloses
• Complex mixture of polysaccharide polymers
• Major constituent of secondary cell wall
• Hemicellulose polymers include: xyloglucan,
glucomannan, galactomannans etc
• Hemicellulases degrade hemicellulose
• Depending on the monomer released after
degradation they are called
Xylanase
Glucanase
Galactanase
Arabinase
Mannase
16. • Fungal pathogens produce enzymes and
oxidative agents (such as activated oxygen
and other radicals) to degrade
hemicellulose
• Eg.Sclerotium rolfsii
– Sclerotinia sclerotiorum
– Diploidia viticola
Southern blight of
tomato
Dead arm of
grapes
17. Lignin
• Found in middle lamella, secondary cell
wall of xylem vessels and the fibers that
strengthen the plants
• Only a small group of microorganism is
capable of degrading lignin- more
resistant to enzymatic degradation than
other plant substances
• Ligninase degrade lignin
18. • Brown rot fungi degrade lignin but not utilise it
• White rot fungi degrade and utilise lignin
• Wood rotting basidiomycetes, several
ascomycetes, imperfect fungi and some bacteria
produce small amount of lignin degrading
enzymes and cause soft rot cavities in wood they
colonise
• Eg.
– Ceratocystis paradoxa (stem bleeding in coconut)
– Polyporus versicolor
– Some spp of Fusarium
– Phellinus spp.
20. Protein
• Proteins have diverse role in the
cellular reactions ( as enzymes) or
as structural materials (in
membranes and cell wall)
• Enzymes degrading proteins are
called Proteases or proteinases or
peptidases
• Proteolytic enzymes produced by most of
the pathogens can affect the organisation
and functions of host cells
22. Starch
• Main reserve of polysaccharides found in
plant cells
• Starch is the glucose polymer containing 2
forms amylose and amylopectin
• Most pathogen utilise starch and other
polysaccharides in their metabolic
activities
• Degradation by enzyme Amylases
• End product is glucose and it is
used by pathogens directly
• Eg: Aspergillus spp
23. Lipids
• Many types of lipids
• Oils and fats in many cells especially in
seeds as energy storage compounds
• Wax lipids- in most aerial epidemal cells
• Phospholipids and glycolipids along with
the proteins –in cell membranes
• Lipolytic enzymes in several fungi,
bacteria and nematodes – Lipases,
phospholipases
24. • Lipolytic enzymes hydrolyse fatty acids and
liberate fatty acids utilised by pathogen
• Some times fatty acids are hyperoxidated by
lipoxygenases or active oxygen molecules
trigger the development of defence
mechanism in plants
• Eg:Sclerotium rolfsii,
– Botrytis cinerea,
– Thielaviopsis basicola
Grey
mould
Black root
rot
