Phytochrome and flowering . When is the right time to flower?

1. Phytochrome and flowering.When is the right time to flower? • Unreliable indicators of time of year • Temperature • Moisture • Light levels • Reliable: length of day/night • Varies with season • Varies with latitude • Detected by phytochrome

2. Sunlight Mostly red A little far red

3. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr In sunlight In sunlight most P gets converted to Pfr form.

4. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Start of night Most P in Pfr form.

5. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr In the dark Pfr form changes gradually to Pr form.

6. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr After a short night much Pfr still remains.

7. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Later in the night more Pfr changes to Pr.

8. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr After a long night all the Pfr is gone.

9. Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Pfr Next day Most P gets converted to Pfr form again.

10. Long day plant = Short night plants • Needs short night to flower • Needs Pfr still present at end of night • Pfr promotes flowering for LDPs

11. Short day plant = Long night plant • Needs long night to flower • Needs Pfr gone at end of night • Pfr inhibits flowering for SDPs Can trick a SDP into not flowering with a brief flash of red light during the long night, this resets much of its phytochrome to Pfr form.

12. LDP SDP Long day: Pfr remains at end of short night. Pfr promotes flowering for LDPs. Pfr inhibits flowering for SDPs. Short day: Pfr gone at end of long night. Lack of Pfr promotes flowering for LDPs. Lack of Pfr inhibits flowering for SDPs.

13. Blue light responses, chapter 18 Phototropism Stomatal opening Chlorophyll and carotenoid synthesis Inhibition of hypocotyl elongation Altered gene expression

14. Phototropism - directional growth toward light. Most evident in dark-grown seedlings.

15. Characteristic blue-light action spectrum Fig. 18.1 “”three finger” pattern

16. Figure 18.2

17. Wild type How does bending toward light happen? Mechanically, what’s going on? 1. Collapse of cells on near side Mutant 2. Increased growth on far side, no change on near side. 3. Reduced growth on near side, no change on far side.

18. Fig. 18.6 Blue light depolarizes the plasmamembrane before reducing growth rate Blue light response causes differential growth by slowing cell expansion on near side. Blue light response is very rapid.

19. Blue light and stomatal opening

21. The blue light effect is not due to increased photosynthesis

22. Fig. 18.11. Action spectrum for blue light stimulated stomatal opening in red light background.

23. Blue light stimulates guard cell H+ pumps.

24. Blue light stimulates a proton pump on guard cell plasmamembrane

25. Blue light regulates osmotic relations of guard cells: H+, K+, Cl- fluxes at plasmamembrane Malate synthesis increases Sucrose synthesis increases K+, Cl-, malate, and sucrose accumulate in vacuole