Transcript Lecture-Mic 621- Galls

‫أ‪.‬د‪ .‬عالية عبد الباقي شعيب‬
‫الر ِح ِيم‬
ِ ‫س ِم‬
ْ ‫ِب‬
َّ ‫من‬
َّ ‫هللا‬
ِ ‫الر ْح‬
WHAT ARE GALLS ?
Galls or plant galls are proliferations and
modifications of plant cells and can be
caused by various parasites, from fungi
and bacteria, to insects and mites.
Galls are often very organised structures
and because of this, the cause of the
gall can often be determined without the
actual agent being identified.
WHAT ARE GALLS ?
This applies particularly to some insect
and mite galls
The Bacterial galls are caused by
several genera of bacteria some of them
are shown in table 1 and those genera
are discussed in this search
WHAT ARE GALLS ?
The pathogen
The disease
Agrobacterim tumifaciens
Crown gall
Rhodococcus fascians
Leafy gall
Pseudomonas syringae
oleander and olive
knot
WHAT ARE GALLS ?
Various gall-forming bacteria employ
some common elements during infection
and symptom development, different
bacteria use distinctive systems to
produce galls.
Except Rhodococcus (Corynebacterium)
fascians and leafy galls are no exception
to this rule (Goethal et al- 2001)
OLEANDER KNOTS
Olive knot is a potentially serious disease of
olives caused by the bacteriaPseudomonas
savastanoi.
Symptoms include rough galls or swellings of variable
size that occur on twigs, branches, trunks, roots,
leaves or fruit stems.
OLEANDER KNOTS
Galls similar to olive knot
have been found in South
Australia and bacteria have
been recovered from these
galls.
Similar galling can be produced on olives by a related
bacterium, which also causes Oleander knot (common in
Australia).
Therefore tests are underway to determine which
bacterium is causing the galling found on olives,
however these are likely to take some time to complete.
Examination of the anatomy of disease galls sheds
light on pathogen biology, symptom development,
and structural defects that lead to plant decline.
Furthermore the Microscopic analyses of plant
galls can provide direct information on the etiology of
galls and effect of disease on host plant anatomy.
For example, early microscopic work on knot
disease of olive , caused by Pseudomonas
savastanoi, established that the pathogen colonizes .
Later studies showed that
Pseudomonas savastanoi colonizes
and spreads through laticifers of
oleander, accounting for the
numerous secondary galls that
developed after inoculation at a
single point. xylem vessels and
fissures within galls.
Aloni et al. described the effects of Agrobacterium
tumefaciens, the crown gall pathogen, on stem
vascular tissues of castor bean. From their
microscopic observations and knowledge of
hormones that control vascular differentiation, they
proposed the “gall constriction hypothesis” to explain
the mechanism by which shoots distal to galls are
deprived of water .
Cranberry stem gall anatomy has been studied
by Violet et al, the disease is characterized by
regions of stem swelling up to several centimeters in
length and small galls on woody runners and
uprights. Eventually galls girdle stems, killing all distal
leaves, flowers, and fruit.
Abnormally large numbers of bacteria (1000-10000
fold greater than in healthy stems), but not other
microbes, have been isolated from galls and the
pathogenicity of several strains of bacteria has been
demonstrated on micropropagated cranberry plants.
The production in vitro of indole-3-acetic acid (IAA)
by bacteria was positively correlated with gall
formation. These findings suggests that IAAproducing bacteria cause cranberry stem gall,
although attempts to reproduce symptoms on woody
plants have not been successful.
Some photographs from Violet et al study are shown
in the next pages.
‫الر ِح ِيم‬
ِ ‫س ِم‬
ْ ‫ِب‬
َّ ‫من‬
َّ ‫هللا‬
ِ ‫الر ْح‬
Some photographs from Violet et al study are shown in the next
Fig. 1. Cross sections of healthy
cranberry stems collected in June.
Sections were embedded in
paraffin, cut on a rotary
microtome, stained with safranin
fast green, and viewed with white
light. A, Low magnification
showing diffuse-porous nature of
cranberry wood. B, Higher
magnification showing phelloderm
(pd) and phellem (p) cells of the
well-developed periderm.
Fig. 2. Cross sections of
cranberry stems with galls
collected in A and B, June or C,
September. Sections were
embedded in paraffin, cut on a
rotary microtome, stained with
safranin/fast green, and viewed
with white light. A well
developed periderm (per) is
pushed away from stems by the
underlying galls. Bacteria (b)
appear as cloudy masses
staining A and B, pink or C, blue.
The vessels of the current year’s
xylem (cx) are narrower and
more numerous than vessels
produced in previous years.
Fig. 3. Cross section of a
cranberry gall at A, lower
and B, higher magnification
showing swirled xylem (x)
that appears to have
differentiated in the gall
rather than from the
vascular cambium. The
section was embedded in
paraffin,
cut on a rotary microtome,
stained with safranin/fast
green, and viewed with
fluorescent light.
Fig. 5. Bacteria within a cranberry gall. The section was embedded in paraffin,
cut
on a rotary microtome, and viewed with fluorescent light. Intense fluorescence
of plant tissue is seen in the upper right and lower right corners of the
micrograph.
Fig. 4. Cross sections of
cranberry galls showing
bacteria (b) A, in cavities and
B, in a fissure near a leaf
trace. Sections were
embedded in paraffin, cut
on a rotary microtome, stained
with safranin/fast green, and
.viewed with white light
Agrobacterium tumefaciens is a Gram-negative
rod-shaped bacterium that is commonly found in
the rhizosphere of many plants, where it survives
on root exudates.
It will infect a plant only through a wound site
(which often occurs in nursery stock through
transplanting and grafting and in vineyards
through pruning).
Agrobaterium is widely recognized for its ability to
transfer foreign DNA into plant cells, whereby T-DNA
becomes integrated into the plant genome.
Certain phenolic compounds produced by the plant
(including acetosyringone) cause the induction of
agrobacterial virulence genes encoding, among other
proteins, an endonuclease that excises T-DNA from the
bacterial tumor-inducing plasmid.
The T-DNA then becomes integrated into the plant
genome, and T-DNA genes are expressed via the
plants normal transcriptional and translational
machinery. Some of the salient features of crown gall
disease were reviewed by Nester et al. (1984), and a
review concerning T-DNA transfer was presented by
Gelvin (2003(.(Eckardt-2006)
2
2
(Aloni et al 2005) discussed some ideas were
experimentally confirmed by showing that tumorinduced ethylene is a limiting and controlling factor of
crown gall morphogenesis; very high ethylene levels
are produced continuously by growing crown galls
during several weeks curve-1; up to 140 times more
ethylene than in wounded, but not infected control
stems, reaching a maximum at five weeks after
infection (Aloni et al. 1998; Wächter et al. 1999).
The vigorous ethylene synthesis in galls is
enhanced by high levels of auxin and cytokinin
(Wächter et al. 1999, 2003).
Furthermore, this ethylene emission induces the
synthesis of considerable concentrations of abscisic
acid in the tumor and host leaves; as a consequence,
transpiration in the leaves slows down to 10% of that of
uninfected plants (Veselov et al. 2003).