Plant Responses to Internal and External Signals

Page
1

Slide 1

Stimuli and a Stationary Life

Linnaeus noted that flowers of different species opened at different times of day and could be used as a horologium florae, or floral clock.

Plants, being rooted to the ground, must respond to environmental changes that come their way.

For example, the bending of a seedling toward light begins with sensing the direction, quantity, and color of the light.

Slide 2

Signal transduction pathways link signal reception to response

Plants have cellular receptors that detect changes in their environment.

For a stimulus to elicit a response, certain cells must have an appropriate receptor.

Stimulation of the receptor initiates a specific signal transduction pathway.

Slide 3

A potato left growing in darkness produces shoots that look unhealthy and lacks elongated roots.These are morphological adaptations for growing in darkness, collectively called etiolation.

After exposure to light, a potato undergoes changes called de-etiolation, in which shoots and roots grow normally.

A potato’s response to light is cell-signal processing: The stages are reception, transduction, and response.

Slide 4

Light-induced de-etiolation (greening) of dark-grown potatoes

(a) Before exposure to light

(b) After a week’s exposure to

natural daylight

Slide 5

Signal Transduction Pathways

CELL

WALL

CYTOPLASM

Reception

Transduction

Response

Relay proteins and

second messengers

Activation

of cellular

responses

Hormone or

environmental

stimulus

Receptor

Plasma membrane

1

2

3

Slide 6

Reception and Transduction

Receptors - Internal and external signals are detected by shape match receptors, proteins that change in response to specific stimuli.

Second messengers transfer and amplify signals from receptors to proteins that cause responses.

Slide 7

Signal Transduction in plants: the role of phytochrome in the de-etiolation (greening) response

CYTOPLASM

Reception

Plasma

membrane

Cell

wall

Phytochrome

activated

by light

Light

Transduction

Second messenger

produced

cGMP

NUCLEUS

1

2

Specific

protein

kinase 1

activated

Slide 8