1. أ.د. عالية عبد الباقي شعيب المملكة العربية السعودية جامعة الملك سعود كلية العلوم قسم البنات والأحياء الدقيقة Mic 621 Bacterial GALLS

2. بِسْمِ اللهِ الرَّحْمنِ الرَّحِيمِ 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.plantparasitesfungibacteriainsectsmites 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.

3. 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

4. The pathogenThe disease Agrobacterim tumifaciensCrown gall Rhodococcus fasciansLeafy gall Pseudomonas syringaeoleander and olive knot WHAT ARE GALLS ?

5. 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)

6. 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.

7. OLEANDER KNOTS 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. Galls similar to olive knot have been found in South Australia and bacteria have been recovered from these galls.

8. 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.

9. 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.

10. 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.

11. 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 IAA- producing 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.

12. 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. بِسْمِ اللهِ الرَّحْمنِ الرَّحِيمِ Some photographs from Violet et al study are shown in the next

13. 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.

14. 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.

15. 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.

16. 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.

17. 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).

18. 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.

19. 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)

20. 2

21. 2

22. (Aloni et al 2005) discussed some ideas were experimentally confirmed by showing that tumor- induced 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).

23. 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).