Plant Responses to Internal and External Signals

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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

Specific

protein

kinase 1

activated

NUCLEUS

1

2

Specific

protein

kinase 2

activated

Ca2+ channel

opened

Ca2+

Slide 9

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

Specific

protein

kinase 1

activated

NUCLEUS

1

2

Specific

protein

kinase 2

activated

Ca2+ channel

opened

Ca2+

Response

3

Transcription

factor 1

Transcription

factor 2

NUCLEUS

Transcription

Translation

De-etiolation

(greening)

response

proteins

P

P

Slide 10

Response

Response - A signal transduction pathway leads to regulation of one or more cellular activities.

In most cases, these responses to stimulation involve increased activity of enzymes.

This can occur by transcriptional regulation or post-translational modification.

Slide 11

Transcriptional Regulation

Specific transcription factors bind directly to specific regions of DNA and control transcription of genes.

Positive transcription factors are proteins that increase the transcription of specific genes, while negative transcription factors are proteins that decrease the transcription of specific genes.

Slide 12

Post-Translational Modification of Proteins

Post-translational modification involves modification of existing proteins in the signal response.

Modification often involves the phosphorylation of specific amino acids.

Slide 13

De-Etiolation (“Greening”) Proteins

Many enzymes that function in certain signal responses are directly involved in photosynthesis.

Other enzymes are involved in supplying chemical precursors for chlorophyll production.

Slide 14

Plant hormones help coordinate growth, development, and responses to stimuli

Hormones are chemical signals that coordinate different parts of an organism.

Any response resulting in curvature of organs toward or away from a stimulus is called a tropism = a growth response.