Plant Defences against disease causing organisms Part I

1. Plant Defences againstdisease causing organismsPart I Resources to support GCSE and A-level curricula by the British Society for Plant Pathology

2. Wind, water, insects and chemotaxis help pathogens reach their hosts

3. Once they reach their host they need to get inside the plant to cause disease .. that’s not so easy. Pathogens must overcome formidable plant defences: physical and chemical barriers

4. Let’s start with the physical …

5. Waxes cover many plant surfaces providing the first physical barrier to pathogen entry. This Scanning Electron Microscope (SEM) image shows waxes around the only ‘weak spot’ in a leaf’s physical barrier – the stomate. Some pathogens head specifically for this opening.

6. The pathogen must gain entry through wax layers, the plant cuticle and the cell wall.

7. In some case, xylem vessels maybe blocked by the formation of tyloses preventing pathogen spread. SEM of xylem vessels

8. Papillae (P) may form on the inner side of cell walls. This structure can trap invading pathogens. Papilla Fungal Infection Peg Fungal spore

9. This SEM image of powdery mildew attacking barley, shows a ‘failed’ papilla (red), and the haustorium (fungal feeding structure) in a barley cell.

10. Plants actively defend themselves against pathogens Plants resist pathogens through active processes that include recognition of the pathogen and defenceresponsesto fight it

11. Inside the Plant the battle continues Mint Witch hazel

12. Anti-microbial compounds inside roots of oat

13. Many chemical reactions occur inside plant cells in response to the invading pathogen

14. Acknowledgements • The BSPP gratefully acknowledges the ASPB for granting access to its Teaching Tools in Plant Biology series. The presentation “Fighting for their lives: plants and pathogens” provided stimulus for this presentation with some slides being used directly (slides 2, 3 & 10) with the editors permission. Herman, M., and Williams, M.E. (June 27, 2012). Fighting for their lives: Plants and pathogens. Teaching Tools in Plant Biology: Lecture No tes. The Plant Cell (online), doi/10.1105/tpc.112.tt0612. • This presentation is prepared under a Creative Commons License, Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0), https://creativecommons.org/licenses/by-nc-sa/4.0/ • Additional images have been sourced as follows. All are within the public domain or used with the authors permission. • Slide 4Water droplets on a leaf surface, Pixabay • Slide 5Image courtesy Dr.Phil Smith, John Innes Centre, Norwich • Slide 6Image courtesy of Dr. Jocelyn Rose, Cornell University, USA. Image first appeared in Plant Physiology (2013), Vol.45 • Slide 7Plant xylem vessels, image courtesy of Mrs. Kim Findlay, John Innes Centre. Schematic – drawn by Dr. Phil Smith (after Agrios, 3rded) • Slide 8Image courtesy Dr.Phil Smith, John Innes Centre, Norwich. • Slide 9Image courtesy Dr. Alan Little, ARC Centre of Excellence in Plant Cell Walls, University of Adelaide, Australia. Image first appeared in New Phytologist (2016), 212:434-443 • Slide 11Mint: Wikipedia (Kham tran) Hamamelis & castle interior, Wikipedia commons • Slide 12Image courtesy of Prof. Anne Osbourn, John Innes Centre, Norwich (NRP image gallery) • Slide 13Image courtesy Dr. Alan Little, Plant Cell Wall group, University of Adelaide Australia. Image first appeared in New Phytologist (2014), 204:650-660