1. PLANT RESPONSES TO INTERNAL AND EXTERNAL SIGNALS Chapter 31

2. Plant Responses - Tropisms Phototropism Gravitropism Thigmotropism Apical Dominance (bud at end of stem inhibits growth of auxillary bud) Abscission – Fruit and Leaf (shedding) Parthenocarpy (production of fruit w/out fertilization) Photoperiodism

3. Tropisms Growth toward or away from a stimulus Gravitropism (Gravity) Phototropism (Light) Thigmotropism (Touch)

4. Gravitropism

5. Plants response to gravity – geotropism Auxins (plant hormone) aka IAA Shoots show negative gravitropism (againsy gravity) Roots show positive gravitropism (with gravity) Statoliths – starch containing plastids detect gravity and causes Auxin to accumulate Auxin concentrates on the “low” side of the stem bending it upward – Shoots respond to high concentrations of IAA Auxin concentrates on the “low” side of the root bending it downward – Roots respond to low concentration of IAA

6. Phototropism Plants response to light Auxin (horomone) Auxin is produced in the apical meristem (end of shoot) of the shoot and travels down by active transport to the zone of elongation. If equally produced then the stem will grow straight Auxin will concentrate on a shady side of a stem Therefore the plant stem will bend toward the light because there is greater elongation on the shady side.

7. Light Darwin and Darwin Phototropism (1880) tip responds to light Tip covered by trans- parent cap Base covered by opaque shield Tip covered by opaque cap Tip removed

8. Light Boysen-Jensen (1913) Phototropism, signal for bending light is actually a mobile chemical, see figure 39.5 Tip separated by gelatin block Tip separated by mica

9. Thigmotropism

10. Plants response to touch Not well understood Vines will climb up walls or trees for support based on touch Some plants respond to touch rapidly – Action potentials similar to nervous system

11. Etiolation (growth in darkness) The stems of plants raised in the dark elongate much more rapidly than normal, a phenomenon called etiolation.

12. Review of Signal Transduction Communication in Organisms – Cell to cell Recognition Glycoproteins and glycolipids – Carbohydrates – Cell Junctions Gap Junctions Plasmodesta – Short Distance Local Regulation – Growth factors – Paracrine Signaling – Synaptic Signaling – Long Distance Hormones CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules Activation of cellular responses Hormone or environmental stimulus Plasma membrane

13. Figure 39.3 CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules Activation of cellular responses Hormone or environmental stimulus Plasma membrane Signal Transduction Pathway

14. De-etiolation (greening up) pathway 1. Light signal detected by phytochrome receptor 2. cGMP stimulates a kinase which stimulates transcription factor 1 OR Ca 2+ stimulates transcription factor 2 3. Translation produces enzymes that cause the plant to green up!

15. Plant hormones help coordinate growth, development, and responses to stimuli Hormones –Are chemical signals that coordinate the different parts of an organism

16. Fill out plant hormone chart

17. Auxin Tutorial http://bcs.whfreeman.com/thelifewire/conten t/chp38/3802003.html http://bcs.whfreeman.com/thelifewire/conten t/chp38/3802003.html

18. Photoperiodism Response of plants to changes in the photoperiod (relative lengths of day and night) Plants detect the color, wavelength, direction, and intensity of light Plants maintain a circadian rhythm – internal biological clock – Phytochromes – absorb red wavelengths of light – P fr – far red – absorbs wavelengths 730 nm (inhibit) – P r - red – absorbs wavelengths 660 nm (smaller wavelength stimulates)

19. Photoperiodism P fr – resets the circadian – rhythm clock P r – synthesized in plant leaves P r and P fr are in equilibrium during daylight P r – accumulates at night P r  P fr at daybreak until equilibrium is reached Length of the night determines the circadian rhythm Plants switch between isomers. P r : absorbs red light, switches to P fr, seed germinates & phytochrome can now absorb far red light for next process

20. Photoperiod: the relative lengths of night and day * Is the environmental stimulus plants use most often to detect the time of year, red light interrupts the photoperiod. Far red light does not. It’s the length of the dark that affects response, not day length.

21. Flowering Plant Groups Long-day – flower in the spring and early summer when daylight is increasing Short-day – flower in the late summer and early fall when daylight is decreasing Day-neutral – do not flower in response to light – Respond to some other environmental cue H 2 O or temperature Floragin hormone triggers flowering of plant based on cue

22. Plant & Pathogen Tutorial http://bcs.whfreeman.com/thelifewire/conten t/chp40/40020.html http://bcs.whfreeman.com/thelifewire/conten t/chp40/40020.html

23. Genetic Control of Flowering Flower formation involves a phase change from vegetative growth to reproductive growth It is triggered by a combination of environmental cues and internal signals Transition from vegetative growth to flowering is associated with the switching- on of floral meristem (permanant embryonic tissue) identity genes

24. ABC Flower Formation Model Plant biologists have identified several organ identity genes that regulate the development of floral pattern The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs