Plant Hormones

Front 1

5 Major Plant Hormone Classes?

Back 1

- Auxins
- Gibberelins
- Cyokinins
- Absicisic Acid (ABA)
- Ethylene

Front 2

Darwin's Experiment (Phototropism)

Back 2

Demonstrated curvature effect.
There's something on the tip of the stem which detects light and grows towards it.

..AUXIN!!

Front 3

What is the function of Auxins (IAA)?

Back 3

- Occurs naturally in plants
- Produced at the top of the plant and is transported downwards, polar transport
- Promotes growth in cells by stem elongation, not by increasing cell numbers
- It accumulates in on the shaded side of cell, or root, to stop elongation (causing a curve).
- Involved in maintenance of apical dominance (lateral growth)
- Promotes root growth
- Stimulates ethylene --> fruit ripening
-

Front 4

Acid growth hypothesis of cell elongation

Back 4

1. Auxin causes cells to pump hydrogen ions into the cell wall
2. pH in the cell wall deceases, activating enzymes that break cross-bridges between cellulose fibres in cell wall.
3. Cellulose fibres loosen and allow the cell to expand as turgor pressure inside the cell pushes against the cell wall.

Front 5

Gibberelins

Back 5

- Promote growth, seed germination and leaf expansion
- causes stem elongation
- involved in 'bolting'
- breaks seed dormancy and stimulates seed germination

Front 6

Cytokinins

Back 6

- Stimulate cell division, cytokinesis.
- growth of lateral branches
- develops in roots and fruit

Front 7

Abscisic Acid (ABA)

Back 7

- Growth inhibitor, assists in toleration of harsh conditions
- Gets stomata in leaves to close by opening k+ Channels under water stress conditions
- Plays major role in seed dormancy
-

Front 8

Ethylene

Back 8

-Gaseous
-involved in plant responses in stressed conditions
-Fruit Ripening
-Influences growth, senescence, flowering

Front 9

Induction of flowering

Back 9

Involves transformation from vegetative to reproductive physiology, and is triggered by physiological maturity and environmental signals such as seasonal changes in day length, monsoons and fire.

Front 10

Detection of photoperiod

Back 10

Phytochrome is a leaf pigment.

Pr is converted to Pfr during the day, but reverts at night. Thus, the amount of Pfr at dawn depends on the length of the night. This interacts with the internal circadian rhythm of 24 hours, leading to the release of the flowering hormone, florigen.