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. PrPr P fr In sunlight P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr In sunlight most P gets converted to P fr form.

4. PrPr P fr Start of night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr Most P in P fr form.

5. P fr In the dark P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr P fr form changes gradually to P r form. PrPr PrPr PrPr PrPr

6. P fr After a short night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr much P fr still remains. PrPr PrPr PrPr PrPr

7. P fr Later in the night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr more P fr changes to P r. PrPr PrPr PrPr PrPr

8. P fr After a long night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr all the P fr is gone. PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr

9. PrPr P fr Next day P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr Most P gets converted to P fr form again.

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

11. Short day plant = Long night plant Needs long night to flower Needs P fr gone at end of night P fr 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 P fr form.

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

13. Blue light responses, chapter 18 1.Phototropism 2.Stomatal opening 3.Chlorophyll and carotenoid synthesis 4.Inhibition of hypocotyl elongation 5.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. How does bending toward light happen? Mechanically, what’s going on? 1. Collapse of cells on near side 2. Increased growth on far side, no change on near side. 3. Reduced growth on near side, no change on far side. Wild type Mutant

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

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: 1.H +, K +, Cl - fluxes at plasmamembrane 2.Malate synthesis increases 3.Sucrose synthesis increases 4.K +, Cl -, malate, and sucrose accumulate in vacuole