1. Plant Responses to Internal and External Signals Chapter 39

3. Plant Hormones  What is a Plant hormone?  Compound produced by one part of an organism that is translocated to other parts where it triggers a response in target cells and tissues.

4. Experiments on Phototropism Discovery of Hormones  1. Darwin and DarwinDarwin and Darwin  Removed the tip of the coleoptile of a grass seedling, and it failed to grow toward light. Removed the tip of the coleoptile of a grass seedling, and it failed to grow toward light.  2. Boysen-Jensen 2. Boysen-Jensen  Put block of gelatin on coleoptile tip to allow chemical diffusion Put block of gelatin on coleoptile tip to allow chemical diffusion  Auxin purified later by Thimann Auxin purified later by Thimann  3. WentWent  Modified Boysen-Jensen experiments Modified Boysen-Jensen experiments  Extracted the chemical messenger responsible Extracted the chemical messenger responsible

5. Functions of Plant Hormones  Control plant growth and development by affecting division, elongation, and cell differentiation  Effect depends on size of action, stage of plant growth and hormone concentration  Hormonal signal is amplified by gene expression, enzyme activity, or membrane properties

6. Five Classes of Plant Hormones  1. Auxins Auxins  2. CytokininsCytokinins  3. GibberellinsGibberellins  4. Abscisic acidAbscisic acid  5. EthyleneEthylene

7. Which hormones cause the following….  Apical dominance from apical bud  Abscission  Stimulates growth of axillary buds  Root growth  Stimulates closing of stomata  Causes fruit ripening  Stimulates seeds to break dormancy and germinate  Growth inhibitor  Cell division and differentiation  Cell elongation  Seedless fruit

8. Answers  Auxin  Ethylene  Cytokinins  Gibberellins  Abscisic acid  Ethylene  Gibberellins  Abscisic acid  Cytokinins  Auxin  Gibberellins

9. Which hormone is made at each location?  Made in roots and transported upwards  cytokinins  Found in meristems of apical buds and seed embryos  auxin  Found in tissues of ripening fruit  ethylene  Leaves stems, roots and green fruit  gibberellins

10. Opposing hormones  Which two hormones act in opposition to one another regarding apical dominance, cell division and differentiation?  Cytokinins and auxins  Which two hormones work in opposition regarding seed dormancy?  Abscisic acid and gibberellins

11. Phototropism

12. Acid Growth Hypothesis

13. Plant Movement  A. Tropisms:  growth response toward or away from stimuli  1. Phototropism  cells on darker side of shoot elongate faster than cells on bright side due to auxin distribution  auxin move laterally across the tip from the bright to dark side by an unknown mechanism.  Cells on the dark side grow

14. Plant Movement  2. Gravitropism (geotropism)  gravity  roots --> positive geotropism  stems---> negative geotropism  Statoliths  starch grains in root cap cells, they trigger calcium redistribution which results in auxin movement in root  auxin inhibits cell elongation  upper side of root elongates faster than bottom

15. Plant Movement  3. Thigmotropism  growth in response to touch  tendrils contacts solid and coils  increased production of ethylene  4. Hydrotropism  growth toward water  willow tree

16. Circadian Rhythms and the Biological Clock  Circadian Rhythm- a physiological cycle with a frequency of about 24 hours that persists even when an organism is sheltered from environmental cues.  Photoperiodism  a physiological response to DAY length  seasonal events

17.  Photoperiods Control of Flowering  the amount of night length controls flowering  1. Short day plantsShort day plants  late summer, fall and winter  2. Long day plantsLong day plants  late spring and summer  3. Day- Neutral plants  unaffected by photoperiods

18. Critical Night Length  Night (dark) actually causes flowering not light  Leaves detect the photoperiod while buds produce flowers  Florigen-  scientists believe this unidentified hormone is produced in the leaves and moves to buds.

20. Phytochrome  Protein containing chromophore (light-absorbing component) responsible for a plant’s response to photoperiod  P r - red absorbing  P fr - Far red absorbing  Plants synthesize Pr in dark  if phytochrome illuminated then Pr--->Pfr  P fr triggers many plant responses to light  In darkness P fr goes back to P r

22. Response to Stress  Water deficit  Flooding  Salt Stress  Heat Stress  Cold Stress  Herbivores

24. Defense Against Pathogens  Gene for Gene relation between plant and pathogen  Coevolution between plant and pathogen

29. Short Day Plant

31.  Spinach Long Day Plant Spinach Long Day Plant

32. Auxins IAA indoleacetic acid: natural auxin  Promotes elongation & secondary growth  Apical meristem is the major site of auxin production  Inhibits lateral growth  Induces female floral parts & fruit

33. Cytokinins  Move from the roots to tissues by moving up xylem  Stimulates protein synthesis  Made in roots  Function:  1. Cell division and differentiation  2. Apical dominance  3. Anti-aging hormones  slow protein deterioration

34. Gibberellins  Stimulate elongation of cells  Inhibits root growth  Stimulate flower part development- bolting  Signals seeds to break dormancy and germinate

35. Abscisic Acid (ABA)  Growth inhibitor  returns seeds to dormancy  inhibits cell division in vascular cambium  causes rapid closing of stoma during dry periods  promotes positive geotropism

36. Ethylene  Gaseous hormone  high [auxin] induce release of ethylene  Senescence (aging)  fruit ripening  Abscission  leaves falling