Plant Responses to Signals IV

1. Plant Responses to Signals IV Photomorphogenesis Circadian RhythmsGravitropism http://sunflower.bio.indiana.edu/~rhangart/plantsinmotion.html

2. General Signal Transduction Signal Transductiongeneral Second messengers, - kinase cascades, - calcium concentration, - etc. Receptors, - G-protein linked, - enzyme linked, - ion channel, - etc. Responses, - gene expression (+/-), - membrane dynamics, - metabolism - cytoskeleton - etc. Signals, - hormone, - light, - temperature, - gravity, - etc. Fig. 39.2

3. ethylene, …or ctr mutant, ein, …blocks pathway. no ethylene …no triple response. active inactive ? induces transcription, no transcription erf: ethylene response factor.

4. Photomorphogenesis • Light is used by plants as a signal, as well as an energy source, • quantity, • quality (wavelength), • direction, • duration. • Germination (+/-) • Stem length (-) • Leaf expansion (+) • Flowering (+/-) • Phototropism (+/-) • Stomatal opening (+) • Chloroplast development (+) • Pigment synthesis (+) • and more...

5. Germination Stem elongation (inhibition) Action Spectra • Action Spectrum, • graph of the magnitude of a biological response to light, • as a function of wavelength.

6. hypothesis Germination Molecular Switch…looking for a photoreceptor, …look for a photo-reversible pigment. Fig. 39.18

7. Pr red light FR light Pfr Phytochromephotoreceptor molecule dimer Fig. 39.19

8. Pr Pfr Quantity, Time, Quality. Phytochromephotoreceptor molecule Fig. 39.20

9. Phytochrome Location Phtyochrome is a cytosolic protein.

10. Phytochrome…has multiple functions, • Seed Germination, • Flowering time (photoperiodism), • Entraining (setting) the biological clock, • End of day, • Stem elongation, • Leaf Expansion, • Pigment synthesis.

11. Short-day plants, …night breaks inhibit flowering. Photoperiodism…flowering times, Long-day plants, …night breaks induce flowering. Fig 39.22

12. …use photoreversibility to establish phytochrome function. Phytochrome…photoperiodism, Fig 39.22

13. Germination Stem elongation (inhibition) Phytochrome absorbtion spectra, …the wavelengths absorbed by specific pigments. not phytochrome

14. Stem elongation (inhibition) Cryptochromes • blue light photoreceptors (I), • …evolved from a light dependent DNA repair enzyme, • ...across phylogeny, these proteins have been used for many functions, • ranging from blue-light-dependent development in plants, • blue-light-mediated phase shifting of the circadian clock in insects, • to a core circadian clock component in mammals.

15. Phototropins…mediate phototropism, • blue light photoreceptors II, • …contribute to stem, root and leaf movements in response to directional information, • …also contributes to the alignment of chloroplasts within mesophyll cells, • to maximize light gathering capacity, • and to minimize light damage at high irradiances. Phototropism action spectrum

16. Photomorphogenesis Functions Concept Map Photoreversible Phytochrome Cryptochrome Photoperiodism Phototropin Action Spectra

17. Circadian Rhythms • Relating to, or exhibiting approximately 24-hour periodicity, • circa around + dies day. • Internal Biochemical Oscillators, • found in all eukaryotes, • eubacteria as well. sleep movements Fig 39.21

18. amplitude • <- Period (24h) -> Circadian Rhythms …of response, Circadian processes continue even if light (or dark) is continuous... Entrainment • …amplitude and period entrainment is continuous, • - allows fine control.

19. ~ 480 of 8,000 (tested) genes are under circadian control, • ~1,500 (estimated) Arabidopsis genes, or ~6% follow circadian cycles of expression.

20. Photosynthesis genes... Secondary metabolism (wood, defense).

21. shoots, …are negatively gravitropic. roots, …are positively gravitropic. Gravitropism … the gravity directed growth processes that direct root and shoot orientation during a plants life-cycle, • about 1.7%, or roughly 500 genes, are transcribed in Arabidopsis when it is re-oriented 90o.

22. Gravitropic Set Point 180o 90o 0o Plant organs orient themselves to the gravity vector.

23. http://www.biosci.ohio-state.edu/~plantbio/Sacklab/timelapse.htmlhttp://www.biosci.ohio-state.edu/~plantbio/Sacklab/timelapse.html Starch Statolith Hypothesis Re-orientation of heavy starch grains signals gravity vector. Fig 39.25

24. Final • All material since Lecture 11 (Reproduction), • lecture, book and other assigned readings (i.e. • Review: 5 pm Monday, (will post room on WEB), • Final, here in this room… • Tuesday 11/9, 10:30 – 12:30.

25. Assigned Essays • Explain the importance of auxin in plants. How it is signaled, what are some of its function, where is it made, how is it transported? Give an example how it interacts with other hormones. • Why would a plant want to prevent self pollination? Discuss two mechanisms used by angiosperms to avoid self fertilization. • Give examples of heterospory and homospory and explain the differences between the two, mentioning the evolutionary significance. • Describe how phase changes are used by developmental biologists to uncover biological processes. • Describe how plants use light and hormones to influence the germination of the seed. • What is phytochrome?

26. Assigned Essays • Explain the importance of auxin in plants. How it is signaled, what are some of its function, where is it made, how is it transported? Give an example how it interacts with other hormones. • Why would a plant want to prevent self pollination? Discuss two mechanisms used by angiosperms to avoid self fertilization. • Give examples of heterospory and homospory and explain the differences between the two, mentioning the evolutionary significance. • Describe how phase changes are used by developmental biologists to uncover biological processes. • Describe how plants use light and hormones to influence the germination of the seed. • What is phytochrome?