Transcript Translocation of Water and Nutrients

EFFECT OF PATHOGENS ON
PLANT PHYSIOLOGY
By Irda Safni
Effect of pathogens on plant physiology:
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Photosyntesis
Respiration
Permeability of cell membrane
Translocation of water and nutrients
Transcription and translation
Plant Growth Hormones
Table 1. Common plant disease symptoms, the physiological process
affected, and examples of a disease
Symptoms
Physiological function
Example of
disease/pathogen
Chlorosis
Photosynthesis
TMV
Wilting
Xylem transport
Bacterial wilt of tobacco, tomato
Hyperplasia – cell division
Growth hormone regulation
Crown gall ; Black knot of plum
(Dibotryon marbosum)
Necrosis
Many different functions
Fire blight of apple
Hyperthrophy – cell enlargement
Growth hormone regulation
Root knots
Leaf abscission
Growth hormone regulation
Coffea rust (Hemileia vastatrix)
Etiolation
Growth hormone regulation
Foolish seedling” of rice (Gibberella
fujikuroi)
Stunting
Many different functions
Man different viral diseases
Abnormal leaf formation
Growth hormone regulation,
respiration
CMV
Photosynthesis
How do pathogens affect plant physiology?
 Interfere by chlorosis, necrosis, and reduced
growth and yield.
 Reduce amount of photosynthetic surface 
affect chloroplast - degenaration
 Produce toxins that inhibit enzymes involved
 Stomata remains unpartially closed 
chlorophyl is reduced & photosynthesis stops
Necrosis of Bacterial leaf spot on lettuce
(Xanthomonas campestris pv. vitians)
Chlorosis of Tomato Splottle Leaf Virus
Photosynthesis
The influence of virus infection :
 Reduction of chloroplast numbers
 Reduction in chlorophyll content
 Chloroplast abnormalities
 Reduction in photochemical activity
 Stimulating CO2 incorporation at early stage of
infection, but declined after virus infection for
several days.
 Reduction in sucrose content
Photosynthesis
The influence of bacterial infection :
Decrease in chloroplast stroma (chloroplast content)
Disorientation of chloroplasts
Destroy of chloroplast integrity - HR
Suppression of CO2 fixation
Hypersensitive Reaction (HR)
E. C. Stakman (1915) is generally credited with
the use of the term, hypersensitive reaction
(HR).
HR involves the extremely rapid death of only
a few host cells which limits the progression of
the infection.
Characteristics of Hypersensitive Reaction
 Cessation of cytoplasmic streaming
 Membrane damage
 Burst of reactive oxygen species
 Protoplast (vacuoles) collapse
 Release of second metabolites – fluorescent
compounds
 Browning of cells
Appearance of HR
42 hpi
120 hpi
Oat Rodney (Pg-2) infected with incompatible isolates of Puccinia
graminis f.sp. avenae Pga-1H
Photosynthesis
The influence of fungal infection :
 Reduce chloroplast RNA content
 Loss of chlorophyll
 Inhibit photophosphorylation coupling mechanism
 Inhibit electron transport
 Suppress CO2 fixation
Photosynthesis
 Stimulation of CO2 fixation in uncolonized leaves
 A stimulation of CO2 fixation in the light is
characteristic of the noninfected leaves of heavily
rusted bean plants.
Altered translocation of organic compounds
Green island on wheat infected with wheat powdery mildew
Green island
Occurred in plant infected by obligate parasite,
such as powdery mildew or rust fungi.
It usually occurred in later stage of disease.
Active starch accumulation and chlorophyll
synthesis.
Green island
Green island has been supposed to be due to
juvenility effect of cytokinins and their action on nutrient
metabolism.
Cytokinin produced at the infection sites exerts a
juvenility effect on tissues and directly govern shortand long-distance movement of nutrients.
The cytokinins increase in rust-infected bean leaves
is of host origin.
Respiration
Respiration increases when plant pathogens
infect leaves because of an increase in leaf cell
permaeability and stomata dysfunction.
Destruction of a considerable portion of the
cuticle and epidermis  an uncontrolled loss of
water from the affected areas.
If water absorption and translocation cannot keep
up with excessive loss of water  loss of turgor
and wilting of leaves.
Respiration
Pathological respiration induced by viruses:
 Respiration rate :
- Nonhypersensitive hosts (systemic hosts)
Slightly increase in respiration rate of inoculated leaves
- Hypersensitive hosts
A much more comsiderable increase in respiration activity
than systemic hosts.
Respiration
Pathological respiration induced by bacteria:
In pepper – Xanthomonas vesicatoria interaction, an
immediate increase in O2 consumption was detected
in resistant tissue, whereas susceptible tissue did not
reflect an increase in respiration until about 30h after
inoculation.
In incompatible interaction, the bacteria usually
caused great increase in respiratory rate.
Respiration
Pathological respiration induced by fungi :
 Respiration rate is usually increased in diseased
plants.
 In the early stage of disease, synthetic processes
induce high rates of respiration, whereas in the late
stages injury and decomposition of tissues lead to
increase respiration.
Respiration
Pathological respiration in resistant hosts
 O2 consumption increases more rapidly in resistant
plants infected either by obligate or facultative parasites
at the early stage of disease; later, the respiration rate
gradually decreases.
Permeability of Host Cell membranes
Permeability of Host Cell membranes
Pathogens can change the permeability of host cell
membranes by mechanical injury, enzymatic
degradation, or toxins.
Changes in cell permeability are often the first
detectable responses of cells to infection by
pathogens.
Permeability of Host Cell membranes
The most commonly observed effect of changes
in cell membrane permeability is the lost of
electrolytes.
Electrolyte leakage occurs much sooner when the
host-pathogen interaction is incompatible, and the
host remains resistant, but when the host is
susceptible and the host develops extensive
symptoms.
Translocation of Water and Nutrients
 Affect the integrity of function of root  absorb
less water
 Growth in xylem vessels interfering with
translocation
 Interfere with water economy of plant by causing
excessive transpiration
Example: Fusarium crown rot
Translocation of Water and Nutrients
Plants infected by viruses:
 Although there are exceptions, virus infection
generally leads to a reduction in transpiration rate,
which is often correlated with a reduced leaf
stomatal aperture.
 Accumulation of carbohydrates in leaf tissue is a
characteristic of severe virus diseases. It is usually
accompanied by phloem necrosis and/or
gummosis, particularly in the later stage of disease.
Gummosis on cherry plant
Translocation of Water and Nutrients
Plants infected by bacteria :
 Bacteria can enter the vascular systems, both
xylem and phloem, through wounds.
 Production of EPS might clot the vascular system
and cause wilting.
Translocation of Water and Nutrients
Infection of Ralstonia solanacearum
on tomato
Infection of Xanthomonas spp. on
banana
Translocation of Water and Nutrients
Plants infected by fungi :
Absorption of water by diseased roots is usually
inhibited.
In vascular wilt diseases, water flow through the
vessels of diseased stems is reduced.
Translocation of Water and Nutrients
In plants with vascular disease, the transpiration
is significantly less than in healthy plants. This
lower transpiration is closely related to the plugging
of vessels and the resultant shortage of water in the
leaves.
Polysaccharides (ex., tyloses) produced by
Fusarium may also be involved in the obstruction of
normal water translocation.
Translocation of Water and Nutrients
Powdery mildew strongly inhibits stomatal
opening, thereby reducing transpiration rate.
However, when epidermis is ruptured, enhanced
transpiration is observed.
Translocation of Water and Nutrients
How do plant pathogens interfere with translocation
in xylem vessels?
Physical presence (mycelium, conidia, bacterial
cells) in xylem
Polysaccharides in the vessels
Collapse of vessels
Development of tyloses
Reduced water tension in vessels due to pathogeninduces alteration in foliar transpiration
Translocation of Water and Nutrients
How do plant pathogens interfere with translocation
of nutrients through phloem?
Pathogen attacks and destroys phloem elements
interferring with downward translocation of nutrient
Starch accumulation in the leaves is a result of
degeneration of the phloem of infected plants (leaf
curling viruses)
Transcription and Translation
Transcription and Translation
Transcription of cellular DNA into messenger RNA &
translation of messenger RNA to produce proteins are
two most basic, general, and precisely controlled
process in the biology of any normal cell.
Disturbance of any of these process may cause
drastic changes in the structure and function of the
affected cells.
Transcription and Translation
Transcription and translation of host cells usually
increase in response to pathogen infection, but
with a higher level for resistant plants, since the
resistant plants need to proceed the defense
reactions.
Transcription and Translation
Effect on Transcription
Several pahogens, particularly viruses & fungal
obligate parasites such as the rusts and powdery
mildews, affect the transcription process in infected
cells.
Pathogens affect transcription by changing the
composition, structure, or function of the chromatin
associated with the cell DNA.
Transcription and Translation
Effect on Transcription
For viruses, through its own enzyme or by
modifying the host enzyme that makes RNA, utilizes
the host cell nucleotides to make its own RNA.
The activity of ribonucleases is increased.
Infected plants (particularly resistant ones) contain
higher levels of RNA than healthy plants, especially
in the early stages of infection.
Greater DNA levels and increased transcription in
cell indicate increased synthesis of substances
involved in the defence mechanisms of plant cells.
Transcription and Translation
Effect on Translation
Infected plant tissues often have increased activity
in several enzymes.
Protein synthesis is increased in infected tissues
of primarily resistant plants.
The increased protein synthesis attacked by
pathogens reflects the increased production of
enzymes and another protein involved in the
defence reactions of plants.
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