Module 6: Plant Responses to stimuli

Tropism

growth movement whose direction is determined by the direction from which the stimulus strikes the plant.

Positive Tropism

form of tropism where the plant, or a part of it, grows in the direction from which the stimulus originates

Negative Tropism

form of tropism where the plant, or a part of it, grows away from the direction which the stimulus originates

Phototropism

the ability of the plant to re-orient the shoot growth towards a direction of light source.

Coleoptile

cylindrical organs that ensheath the first leaf and shoot apex in grass seedlings

Phototropism will fail to occur and it will not bend to the direction of light

What will happen if the coleoptile is covered?

There will be no interference in the phototropism and the plant will bend in the direction of light.

What will happen if the plant is covered but the coleoptile is still exposed?

Phototropins

proteins that receive blue light during phototropism

releases hydrogen ions in the shaded region of the stem which causes a decrease in the pH.

How does auxin affect the growth of the plant during phototropism?

activates expansin that causes the cells to swell and forces the stem to bend towards the light.

Explain what happens when pH level is decreased during phototropism

the darker side of the stem

Which side does auxin move when exposed to light?

Etiolation

phenomenon where plants grown in the dark have elongated stems, are white or yellow (due to lack of chlorophyll), and have small leaves.

Etioliation

a mechanism that increases the chance that the plant will access light.

Gibberellins

plant hormones that promote stem elongation thus mimicking the etiolation response.

Gravitropism (geotropism)

occurs when a plant is placed on its side and the roots are elongated

Statoliths

organelles containing starch grains

Bottom of the cells in the root tip

Where does the statolith settle by gravity?

auxin (IAA)

What is pumped outside of the cell when pin proteins are redistributed?

under side of the root

Where does auxin accumulates during gravitropism?

inhibit root cell elongation

What does auxin cause during gravitropism?

Nastic movement

non-directional responses to stimuli

Tropic movement

the movement of the plant in response to the stimulus present in the environment

Independent

Nastic - growth

Dependent

Trophic - growth

Immediate

Nastic - time of action

Slow

Tropic - time of action

Non-directional

Nastic - response to stimulus

Directional

Tropic - response to stimulus

Change in turgor

Nastic - reason for action

Cell division

Tropic - reason for action

Sensence

Term relating to "ageing"

Fruit ripening

ethylene stimulates the conversion of starch and acids to sugars

abscission

natural detachment of parts of a plant

Senescence and cell death

What happens to when ethylene when auxin level decline?

Giberellin, auxin, cytokinin, ethylene, abscisic acid

Five common gases in plants

expansin

What is activated when pH level is decreased?

geotropism - (plant part - shoot) In the light it is

positive

geotropism - (plant part - root) In the light it is

negative

geotropism - (plant part - root) In the gravity it is

positive

geotropism - (plant part - shoot) In the gravity it is

negative

Hydrotropism

Growth/movement in response to **water**

responsible for the response to hydrotropism, which induces differential growth in plant parts/ in response to water

Abscisic Acid (ABA)

Thigmotropism

Growth/movement in response to **touch/contact**

It is also called Haptotropism

Thigmotropism

Auxin -> Growth -> Ethylene -> Changed in Turgidity

Mechanism of Thigmotropism

It changes turgidity (movement) of stem

Ethylene

Growth/movement in response to **heat**

Thermotropism

Some plants protect leaves during periods of high irradiance by sunlight or from cold temperature (tumitiklop ang mga leaves)

Thermotropism

Growth/movement of in response to **chemical stimuli**

Chemotropism