CH- 27

1. CH- 27 • Control of plant growth and Response CH-27 Control of Plant Growth and Responses in Plants

2. 27.1 Plant Responses • Environment – gravity, light, seasons…. • Opening stomata at dawn • changing growth patterns • Mechanism – how do plants control their growth and responses to the environment? HORMONES CH-27 Control of Plant Growth and Responses in Plants

3. 27.1.1 Tropisms – plant responses • Growth or toward or away from a directional stimulus. CH-27 Control of Plant Growth and Responses in Plants

4. Phototropism - • Light stimulus • toward – positive • away – negative – • AUXIN – on shady side – cells grow faster • Stem bends toward the light CH-27 Control of Plant Growth and Responses in Plants

5. Gravitropism – (Geo) • gravity • root cap produces hormones – meristem • Root and stem tissues respond differently to the same hormone – AUXIN • In stems - Auxin on lower side, causes stem to bend away from gravity. • In roots Auxin on lower side of root – causes bending root towards gravitational center. CH-27 Control of Plant Growth and Responses in Plants

6. Thigmotropism: - touch • Unequal growth - contact with solid objects • Tendrils – coiling about a branch • Stroking - response initiator. • ATP required and 2 hormones • Auxin and Ethylene CH-27 Control of Plant Growth and Responses in Plants

7. THIGMOMORPHOGENESIS • Thigmotropism - Entire plant responds • stunted growth • branches flagging in one direction. • Mechanical Stimulation – can inhibit cell elongation, making plant sturdier. • Apple trees CH-27 Control of Plant Growth and Responses in Plants

8. 27.1a NASTIC MOVEMENTS • Independent of direction of a stimulus • Growth NOT involved • SEISMONASTIC MOVEMENTS - • TOUCH • SHAKING • THERMAL STIMULATION CH-27 Control of Plant Growth and Responses in Plants

9. Sleep movements – are Nastic • RESPONSE TO CHANGES IN LIGHT AND DARK PERIODS • CIRCADIAN RHYTHM – 24 hr biological cycle. • Persist Even If environmental stimulus is absent--- • Internal BIOLOGICAL CLOCK • SET by/to PHOTOPERIOD – day length vs length of night. CH-27 Control of Plant Growth and Responses in Plants

10. 27.2 PLANT HORMONES • Chemical messengers. • Stem and root elongation and tropisms. CH-27 Control of Plant Growth and Responses in Plants

11. Hormones are moved • via Phloem • From one part of the plant to another • OR • Passed from cell to cell CH-27 Control of Plant Growth and Responses in Plants

12. 27.2a AUXINS CH-27 Control of Plant Growth and Responses in Plants

13. AUXINS – restrain and promote growth • IAA – Indole Acetic Acid - • new shoots (apical meristem) and leaves • flowers, fruits • APICAL DOMINANCE. • Apically-produced auxin - –auxin on a woody cutting - adventitious roots. • Prevents leaves and fruits from dropping CH-27 Control of Plant Growth and Responses in Plants

14. 27.2b GIBBERELLINS – Growth Promoters GA3 Is the most common – there are GA 1,N • CAUSE THE ELONGATION OF CELLS • CAUSE STEMS TO ELONGATE – • CAUSE SEEDS TO BREAK DORMANCY • INCREASE FORMATION OF ENZYMES THAT RELEASE ENERGY NEEDED FOR GROWTH. CH-27 Control of Plant Growth and Responses in Plants

15. 27.2.3 CYTOKININS • Promote cell division (Cytokinesis) • Cytokinins - prevent aging and delay death due to age. • initiate leaf growth • overide apical dominance. CH-27 Control of Plant Growth and Responses in Plants

16. Senescence • aging process • Large molecules in leaf are broken down • IN LEAVES : loss of color CH-27 Control of Plant Growth and Responses in Plants

17. 27.2 Inhibitory Hormones: • Two plant hormones INHIBIT Growth CH-27 Control of Plant Growth and Responses in Plants

18. ABSCISIC ACID (ABA) - INHIBITS GROWTH • “Stress hormone” initiates and maintains seed and bud dormancy • Closes stomata CH-27 Control of Plant Growth and Responses in Plants

19. 2 - ETHYLENE : • INHIBITS GROWTH. (@ 0.01 PPM ) • THE Ripening hormone - ripens fruit • Ethylene is released as a gas into the air “ONE ROTTEN APPLE……..” • INVOLVED IN ABSCISSION - dropping of leaves, flowers and fruits FROM PLANTS • Stimulates CELLULASE production. CH-27 Control of Plant Growth and Responses in Plants

20. 27.3 PHOTOPERIODISM • Changes in plant physiology are tied to length of day. • seed germination • breaking of bud dormancy • senescence CH-27 Control of Plant Growth and Responses in Plants

21. PHOTOPERIODISM: 1 Short-day plants: • flower when day length is shorter than some critical period. 2 Long-day plants: • day length is longer than some critical period 3 Day-neutral plants: • flowering is independent of day length – CH-27 Control of Plant Growth and Responses in Plants

22. LENGTH OF DARKNESS IS CRITICAL • FOR SHORT-DAY PLANTS AND LONG-DAY PLANTS – • THE LENGTH OF THE DARK PERIOD IS CRITICAL, NOT THE PERIOD OF LIGHT. CH-27 Control of Plant Growth and Responses in Plants

23. PHYTOCHROME AND Plant Flowering • A blue-green leaf pigment involved in response of plant to photoperiod. CH-27 Control of Plant Growth and Responses in Plants

24. Two forms: • Pr – ABSORBS RED LIGHT  CONVERTED TO Pfr • Pfr – absorbs far-red light = converted to pR • MORE RED LIGHT IN DIRECT SUNLIGHT • IN SHADE Or AT SUNSET/SUNRISE THERE IS MORE FR LIGHT. • PLANT CAN DETECT CHANGES IN PHOTOPERIOD by ratio of Pr to Pfr CH-27 Control of Plant Growth and Responses in Plants