1. Plant Responses to Internal and External Environment Chapter 39

2. Review of Basic Plant Parts root shoot apex These are the parts of the plant we will be concerned with today flowers

3. Hormonal Control Hormone binds to receptor Triggers second messengers Cell responses (greening, flowering, etc) take place

4. Plant Hormones Auxins Produced in embryo, apical meristems Stimulates root growth, stem elongation Cytokinins Made in root, transported to other parts Stimulates cell division, plant growth Gibberelins: Made in meristematic tisssues Promotes bud/seed germination, stem elongation

5. Plants exposed to gibberellins Normal dwarf plant Dwarf plant treatedw ith gibberellin

6. Elongation of Cells 1. Proton pumps transport auxin produced in apical meristem into cell 2. Proton pumps move H+ ions into cell wall matrix 3. Acidity in cell wall increases so that cross bridges in cellulose breaks 4. Cell wall weakens, water enters and cellulose fibers stretch 5. Cell elongates, and cell produces more cytoplasm and organelles

7. Control of Apical Dominance Apical dominance: plant will grow tall with evenly distributed lateral growth Auxin produced by terminal bud inhibits growth of lateral buds

8. Control of Apical Dominance When terminal bud trimmed: Cytokinins produced by roots stimulates axillary bud growth Axillary buds grow, plant gets bushier

9. Root growth Auxins: stimulate root branching Cytokinins: inhibit root branching

10. Tropic responses Tropisms: plant responds to environmental stimulus and moves Phototropism Gravitropism Thigmotropism

11. Phototropism Plants move toward the light when exposed to it Positive: toward light

12. Phototropism Light shines directly on plant tip: plant grows straight up since auxin concentration is high

13. Phototropism When light is at angle, auxin accumulates on shaded side This stimulates cell elongation Increased chemical messenger on sunny side inhibits cell elongation Result: Stem grows toward light source

14. Gravitropism Plants move toward or away from gravity’s pull

15. Gravitropism: Roots Starch grains settle to bottom of root cells Causes migration of Ca +2 ions Auxin moves laterally

16. Gravitropism: Roots 1. Low auxin conc. stimulates cell elongation 2. High auxin conc. inhibits cell elongation Result = root curves downward 3. Low auxin conc. inhibits cell elongation 4. High auxin conc. stimulates cell elongation Result = shoot curves upward

17. Thigmotropism Plants curl around objects or react to being touched Mimosa trees Venus fly traps Tendrils of vines

18. Photoperiodism Plants use light to determine when to flower, germinate seeds, break bud dormancy

19. Control of Flowering Key Concepts Phytochromes: pigments that regulate plant response to light Critical night length: the minimum amount of night time required for regulation of plant growth

20. Short-day plants light dark Critical night length If light exceeds or interrupts critical night length, no flowering happens.

21. Long-day plants light dark Critical night length Night can exceed critical night length or be interrupted, flowering can still happen.

22. Control of Fruit Ripening Ethylene gas: not really a hormone, but plays a role in fruit ripening Hastens fruit ripening “One bad apple spoils the bunch”

23. Plant Defenses Plants produce volatile chemicals in response to predation: secondary compounds Also, antioxidants to protect against UV rays