1. Cells and cell growth Membranes and cell walls Fertilization and embryogenesis Seed development and dormancy Germination Water transport Water relations Plant nutrition Solute transport Gene function Skotomorphogenesis Photomorphogenesis Phytochrome

2. Three learning goals: - what is a phytochrome plant photoreceptor to govern light development requirements: light sensing ability signal transduction - phytochromes and their integration in development how phytochrome senses light and what happens then requirements: light sensitivity at particular wavelengths - phytochrome interactions with downstream proteins requirements: signal transduction apparatus that connects phytochrome activity with gene regulation

4. In a nutshell: phytochrome function

5. Phytochrome – plant signal transduction Environmental signal: light Receptor: phytochrome Signal transduction: PIF etc. Gene activation: PIGs Biological response: photomorphogenesis

6. Photomorphogenesis Skotomorphogenesis (etiolation)

8. Germination of lettuce seeds (photoreversibility) Reversible R/FR response system controlled by phytochrome germination

9. Pr Pfr Red light Far-red light inactive active Phytochrome dogma

10. synthesis germination, flower Induction…… red light far red light Phytochrome: from synthesis to action

11. blue lightred light

12. Arabidopsis: 5 phytochrome proteins (phyA - phy E), differ in their apoproteins Phytochrome : homodimeric chromoprotein: apoprotein and phytochromobilin (open chained tetrapyrrol) as chromophor form holoprotein

13. Strasburger, 2002 RFR PR inactive PFR active P FR active P R inactive sensor signal transduction Regulatory function

14. Strasburger, 2002 Structure of phytochrome proteins

15. Phytochrome responses vary with amount of light VLFR: 0.00001 µmol x m -2 LFR: 1-1000 µmol x m -2 Arabidopsis seed germination Lettuce seed germination Anthocyanin synthesis Inhibition of hypocotyl elong. Enlargement of cotyledons Apical hook opening HIR: >1000 µmol x m -2 x s -1

16. Phytochrome responses vary with amount of light Inhibition of hypocotyl elongation HIR: >1000 µmol x m -2 x s -1

17. Phytochrome responses vary with amount of light LFR: 1-1000 µmol x m -2 Lettuce seed germination

18. Strasburger, 2002 Shade avoidance reaction

19. Sunlight and CO 2 have different effects on leaf morphology

20. What happens in the shade?

22. Pr Pfr Red light Far-red light Photoequilibrium: 660 nm 80% Pfr 730 nm 2-3% Pfr R/FR Sunlight:1.13 Dusk: 0.8/0.9 Shade of leaves:0.2 inactiveACTIVE !!!

23. Strasburger, 2002 Shade avoidance reaction

24. Strasburger, 2002 Shade avoidance reaction

25. Strasburger, 2002 Shade avoidance reaction

26. PHYA-GFP and PHYB-GFP fusion proteins migrate into the nucleus PHYA-GFP PHYB-GFP Dark Red

27. Gene activation through phytochrome Nuclear import DNA binding Gene activation

28. Red light Far-red light Pr Pfr Two holoproteins (+chromophore) form a dimer Histidine kinase related Chromophore binding domain IIA IA IIB IB IA IIA IIBIB

30. Germination in dark and light

32. Gene activation through photoreceptors and PIF proteins Hemara