1. Botany: Part IV Plant Signaling

2. Plant Responses Plant _____________ trigger a signal transduction pathway 2

3. 3 Tropisms A _______________ is the turning or bending movement of an organism or a part toward or away from an external ______________, such as light, heat, or gravity.

4. 4 Tropisms What are these plants responding to?

5. Plant Hormones _____________- stimulate cell elongation, responsible for tropisms _____________-stimulate cytokinesis or cell division, and cell differentiation _______________- stimulate cell elongation in stems _______________-promotes seed dormancy, slows growth _______________- gas, promotes ripening of fruit and cell death 5

6. Plant Response to Light Plants can detect light’s direction, intensity, and wavelength. Light receptors are called __________________________. 6

7. Photoperiodism _______________________ is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. In the 1940s researchers learned photoperiodism is ____________________________. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of the light and dark periods. 7

8. Short-Day Plants ________________ (long-night) plants flower when night exceeds a critical dark period. A flash of light interrupting the dark period ________________flowering. Examples: Chrysanthemums, poinsettias and some soybean plants generally flower in late summer, fall or winter. 8

9. Long-Day Plants ___________________ (short-night) plants flower only if the night is shorter than a critical dark period. A brief flash of light artificially interrupts a long dark period, thereby _______________________ flowering. Examples: spinach, radishes, lettuce, irises and many cereal varieties are long-day plants. 9

10. Photoperiodism To flower or not to flower? That is the question. (Apologies to Shakespeare) 10 

11. Geotropism (or Gravitropism) ___________________ or gravitropism turning or growth movement by a plant or fungus in response to gravity. 11

12. Response to Other Stimuli ________________________ is a movement in which a plant moves or grows in response to touch or contact stimuli. 12