1. What is a hormone?
Hormones- chemical messengers
Chemical Control in Plants depend on :
The hormone involved
Concentration [ ]
Tissue affected by the chemical

2. Main types of hormones in plants
Auxins- “plant regulators” chemicals that stimulate or slow(inhibit) growth by influencing cell division, elongation, and cell differentiation (specialization of cells).

3. Example of an auxin
IAA (Indole acetic acid)- [High] in the terminal buds, causes a lateral bud to grow, explaining why plants become bushier when cutting off terminal buds.
Terminal bud
lateral bud

4. Gibberellins-affect plant growth of stems, roots, & leaves.
stimulate flowering and increases size of fruits.
[ 50 or more have been found in plants, algae, & fungi]
Sprayed with Gibberellins

5. Other hormones
Cytokinins- stimulate cell division and growth during seed germination.
Ethylene- stimulates ripening of fruits (bananas). Also, plays a role in abscission (slowing down of plant activities & dropping of leaves, flowers, or fruits).
Abscisic acid- associated with shedding leaves and seasonal slowing down of plant activities. [Higher] in the fall.

6. Why use plant regulators?
Weed killers – chemicals causes dandelions to grow abnormally & die.
Affects monocots (grass) less than dicots. Used to rid (Monocot) corn fields of weeds.
Stimulate root formation for cuttings- rooting powders aid in propagation
To produce seedless fruit- auxins applied to ovaries of some flowers causes them to develop into fruits w/out pollination.
Prevent fruit from falling before maturity

7. Types of Tropisms
Tropisms- a growth of part of a plant in a specific direction in response to a stimulus.
Positive – growth toward a stimulus
Negative- growth away from a stimulus
Phototropism – light
Plants always grow toward the light [positive phototropism]

8. Geotropism- (gravity)
Roots generally grow down into the ground [positive geotropism]

9. Chemotropism- chemicals
Thigmotropism- touch
( gravevine winds around stem of another plant)
Hydrotropism – water
Willow trees roots grow toward water

10. Nastic Movements- plant movements in response to a stimulus, but independent of the direction of the stimulus.
Leaves of a prayer plant are spread out flat during day, but become vertical at night.

11. Sensitive plant- if touched collapse due to a change in osmotic pressure. [ions] drops when touched forcing water out and cells lose turgor & collapse.
Venus fly trap- when trigger hairs on leaves are touched, cells lose solute & water moves out of cells. When water pressure is restored plants open.

12. Photoperiodism- the response of a plant to changes in the length of day or night.
Long day (short night)- flower when shorter periods of darkness. Ex. Clover, potato, beet, gladiolus, poppy [bloom in summer]

13. Short day (long night)- flower when longer periods of darkness. Ex
Short day (long night)- flower when longer periods of darkness. Ex. Morning glory, tulip, forsythia [bloom in late spring, late summer or fall]
Day neutral plants- are unaffected by lengths of light & dark Ex. String beans, corn, tomato, cucumber