1. Control Systems in Plants

2. 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.

3. Phototropism

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-JensenBoysen-Jensen –Put block of gelatin on coleoptile tip to allow chemical diffusionPut block of gelatin on coleoptile tip to allow chemical diffusion –Auxin purified later by ThimannAuxin purified later by Thimann 3. WentWent –Modified Boysen-Jensen experimentsModified Boysen-Jensen experiments –Extracted the chemical messenger responsibleExtracted 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. AuxinsAuxins 2. CytokininsCytokinins 3. GibberellinsGibberellins 4. Abscissic acidAbscissic 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. Which hormone is made at each location? Made in roots and transported upwards –Cytokinins Found in meristems of apical buds and seed embryos Found in tissues of ripening fruit –Ethylene Leaves stems, roots and green fruit

9. 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 & gibberellin

10. 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. 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 –upperside of root elongates faster than bottom

15. 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 & 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.

21. 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

24. Response to Stress Water deficit Oxygen deprivation Salt Stress Heat Stress Cold Stress Herbivores…

26. 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

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

36. 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

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

38. 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

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