1. Ch. 39 Plant Responses to Internal and External Signals Objectives: LO 2.29 The student can create representations and models to describe immune responses. LO 2.30 The student can create representations or models to describe nonspecific immune defenses in plants and animals. LO 2.35 TSIAT design a plan for collecting data to support the scientific claim that the timing and coordination of physiological events involve regulation. LO 2.36 TSIAT justify scientific claims with evidence to show how timing and coordination of physiological events involve regulation. LO 2.37 TSIAT connect concepts that describe mechanisms that regulate the timing and coordination of physiological events. LO 2.38 TSIAT analyze data to support the claim that responses to information and communication of information affect natural selection. LO 2.39 TSIAT justify scientific claims, using evidence, to describe how timing and coordination of behavioral events in organisms are regulated by several mechanisms. LO 2.40 TSIAT connect concepts in and across domain(s) to predict how environmental factors affect responses to information and change behavior.

2. Overview Since plants cannot move (away from threats or toward a resource) they respond to cues by adjusting their individual patterns of growth and development. ◦ Ex: opening of flowers for pollinator when they are active.

3. 39.1 Signal Transduction Pathways Link Signal Reception to Response Etiolation: morphological adaptations for growing in the dark. ◦ Ex: a potato puts its resources into producing stems because it is located under the soil.  When exposed to light, the stem stops growing and leaves with chlorophyll are produced (de-eiolation) (a) Before exposure to light (b) After a week’s exposure to natural daylight

4. Reception Phytochrome receptors in the cytoplasm of plants. Transduction Phytochrome: ◦ opens Ca 2+ channels (increases its concentration) ◦ changes shape activating cyclic GMP (These are second messengers relay and amplify the signal to response proteins) Response Post-translational – activates preexisting enzymes Transcriptional – increases mRNA synthesis

5. Figure 39.4-3 Reception 23 1 Transduction Response CYTOPLASM Plasma membrane Phytochrome Cell wall Light cGMP Second messenger Ca 2  Ca 2  channel Protein kinase 1 Protein kinase 2 Transcription factor 1 Transcription factor 2 NUCLEUS Transcription Translation De-etiolation (greening) response proteins P P

6. 39.2 Plant Hormones Help Coordinate Growth, Development, and Response to Stimuli The discovery of plant hormones Tropism: growth response toward or away from a stimulus. ◦ Ex: plants grow toward light (phototropism)  (Darwins) A hormone is produced in the coleoptile that is transmitted down the stem to have cells facing the light slow growth and cells not facing the light grow faster. Control Light Shaded side Illuminated side Boysen-Jensen Light Darwin and Darwin Gelatin (permeable) Mica (impermeable) Tip removed Opaque cap Trans- parent cap Opaque shield over curvature RESULTS

7. Frits Went placed the coleoptile tip on agar. The agar contained a hormone. When placed on one side of the plant, that side began to grow causing it to bend. Auxin (indoleacetic acid) is the hormone produced which causes cell elongation (a plant growth hormone). Control RESULTS Excised tip on agar cube Growth-promoting chemical diffuses into agar cube Control (agar cube lacking chemical) Offset cubes

8. © 2011 Pearson Education, Inc. Video: Phototropism

9. HormoneWhere produced/foundMajor Functions AuxinShoot apical meristems and young leaves Stimulates stem elongation CytokininsRootsRegulate cell division GibberellinsMeristems of buds and rootsStimulates stem elongation, reproduction BrassinosteroidsAll tissuePromote cell expansion Abscisic acid (ABA)All tissueInhibits growth StrigolactonesRootsPromote seed germination EthyleneAll tissuePromotes ripening of fruits

10. 39.3 Responses to Light Are Critical For Plant Success Blue-Light Photoreceptors ◦ Phototropism ◦ Opening stomata ◦ Slowing hypocotyl growth once seedling breaks ground. (b) Coleoptiles before and after light exposures Light Time  0 min Time  90 min

11. Phytochormes as Photoreceptors ◦ Protein which absorb red light which stimulates germination. ◦ Discovered by exposing seeds to different colors of light then observing them. RESULTS Red Far-red Dark (control) Dark

12. ◦ Phytochromes also serves as a shade avoidance indicator. ◦ When in shade, far-red light is more abundant leaving the protein “inactive.” ◦ This tells the plant it is in shade and needs to grow taller. Synthesis PrPr P fr Red light Far-red light Slow conversion in darkness (some plants) Responses: seed germination, control of flowering, etc. Enzymatic destruction

13. Biological Clocks and Circadian Rhythms Circadian rhythms are cycles that occur every 24 hours which are not directly controlled by any known environmental variable. ◦ Putting plants in a controlled environment (24 hours of light) only slightly get the rhythm off course (21-26 hour rhythms). Noon Midnight

14. Photoperiodism A physical response to the relative lengths of night and day. ◦ Night time requirements not to be broken by light or flowering won’t occur. ◦ Ex: short day plants need uninterrupted long nights to flower (Long-night plants) 24 hours Light Flash of light Darkness Critical dark period Flash of light (b) Long-day (short-night) plant (a)Short day (long-night) plant

15. 39.4 Plants Respond to a Wide Variety of Stimuli Other Than Light Gravity (gravitropism) ◦ Positive = downward growth of roots ◦ Negative = upward growth of shoots ◦ Detected by statoliths (cytoplasmic components that settle to the bottom of the cell). Statoliths 20  m (a) Primary root of maize bending gravitropically (LMs) (b) Statoliths settling to the lowest sides of root cap cells (LMs)

16. © 2011 Pearson Education, Inc. Video: Gravitropism

17. Mechanical Stimuli (being “touched”) ◦ Thigmomorphogensis are changes in the form of a plant due to mechanical stimuli (wind, touch, water, etc) (a) Unstimulated state (b) Stimulated state

18. © 2011 Pearson Education, Inc. Video: Mimosa Leaf

19. Environmental Stresses (abiotic) Drought ◦ Plants lose water by transpiration and cannot replenish it. ◦ Responses: shed leaves, curl leaves, close stomata, root growth Flooding ◦ suffocates roots/no oxygen Salt ◦ Loss of water in soil ◦ Toxic to plants Heat ◦ Denatures enzymes Cold ◦ Loss of fluidity of cell membranes slowing/stopping transport in/out of cell.

20. 39.5 Plants Respond to Attacks by Herbivores and Pathogens Defense against herbivores ◦ Physical defenses  Thorns ◦ Chemical defenses  Distasteful or toxic compounds  Canavanine (replaces arginine when ingested)  Attraction of parasitoid wasps Wounding Signal transduction pathway Chemical in saliva Synthesis and release of volatile attractants Recruitment of parasitoid wasps that lay their eggs within caterpillars 2 11 3 4

21. Defense against pathogens ◦ First line of defense is the epidermis and periderm of plant body. ◦ Plants can recognize pathogen-derived molecules (effectors) causing the plant to either respond defensively or be taken over by the pathogen. ◦ The Hypersensitivity Response  cells near infection site secrete toxins then die to prevent the spread of infection. R protein Avr effector protein R-Avr recognition and hypersensitive response Infected tobacco leaf with lesions Signal Hypersensitive response Avirulent pathogen Signal transduction pathway 2 4 3 1

22. Systemic Acquired Resistance ◦ General response putting whole plant “on alert” ◦ Production of salicyclic acid in areas away from infection, activating a signal transduction pathway to produce pathogenesis-related (PR) proteins Systemic acquired resistance R protein Avr effector protein R-Avr recognition and hypersensitive response Signal Hypersensitive response Signal transduction pathway Acquired resistance Avirulent pathogen Signal transduction pathway 2 4 3 5 1 7 6