Slide #1.

Plant Responses to Signals IV Photomorphogenesis Circadian Rhythms Gravitropism http://sunflower.bio.indiana.edu/~rhangart/plantsinmotion.html
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Slide #2.

Signal Transduction general Receptors, Second messengers, - kinase cascades, - calcium concentration, - etc. Responses, - G-protein linked, - enzyme linked, - ion channel, - etc. - gene expression (+/-), - membrane dynamics, - metabolism - cytoskeleton - etc. Signals, - hormone, - light, - temperature, - gravity, - etc. General Signal Transduction Fig. 39.2
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Slide #3.

no ethylene ethylene, ein, …no triple response. …or ctr mutant, …blocks pathway. active inactive ? erf: ethylene response factor. induces transcription, no transcription
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Slide #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... (+)
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Slide #5.

Germination Action Spectra • Action Spectrum, – graph of the magnitude of a biological response to light, – as a function of wavelength. Stem elongation (inhibition)
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Slide #6.

Molecular Switch …looking for a photoreceptor, hypothesis Germination …look for a photo-reversible pigment. Fig. 39.18
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Slide #7.

Phytochrome photoreceptor molecule Pr red light FR light dimer Pfr Fig. 39.19
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Slide #8.

Phytochrome Quantity, Time, Quality. photoreceptor molecule Pr Pfr Fig. 39.20
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Slide #9.

Phytochrome Location Phtyochrome is a cytosolic protein.
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Slide #10.

Phytochrome …has multiple functions, • Seed Germination, • Flowering time (photoperiodism), • Entraining (setting) the biological clock, • End of day, • Stem elongation, • Leaf Expansion, • Pigment synthesis.
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Slide #11.

Photoperiodism …flowering times, Long-day plants, Short-day plants, …night breaks induce flowering. …night breaks inhibit flowering. Fig 39.22
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Slide #12.

Phytochrome …photoperiodism, …use photoreversibility to establish phytochrome function. Fig 39.22
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Slide #13.

Germination Phytochrome Stem elongation (inhibition) absorbtion spectra, …the wavelengths absorbed by specific pigments. not phytochrome
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Slide #14.

Cryptochromes Stem elongation 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-lightdependent development in plants, • blue-light-mediated phase shifting of the circadian clock in insects, • to a core circadian clock component in mammals. (inhibition)
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Slide #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
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Slide #16.

Concept Map Functions Photoreversible Phytochrome Cryptochrome Photoperiodism Photomorphogenesis Phototropin Action Spectra
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Slide #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
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Slide #18.

Circadian Rhythms amplitude …of response, Circadian processes continue even if light (or dark) is continuous... Entrainment …amplitude and period entrainment is continuous, <- Period (24h) -> - allows fine control.
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Slide #19.

~ 480 of 8,000 (tested) genes are under circadian control, • ~1,500 (estimated) Arabidopsis genes, or ~6% follow circadian cycles of expression.
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Slide #20.

Photosynthesis genes... Secondary metabolism (wood, defense).
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Slide #21.

shoots, …are negatively 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. roots, …are positively gravitropic.
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Slide #22.

Gravitropic Set Point 180o 90o 0o Plant organs orient themselves to the gravity vector.
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Slide #23.

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