Plant Responses to Internal and External Signals

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Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection.

The effects of ethylene include response to fruit ripening, mechanical stress, senescence, and leaf abscission.

Fruit Ripening

A burst of ethylene production in a fruit triggers the ripening process.

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Ethylene

The Triple Response to Mechanical Stress

Ethylene induces the triple response, which allows a growing shoot to avoid obstacles.

The triple response consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth.

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ethylene-induced triple response

Ethylene concentration (parts per million)

0.10

0.00

0.20

0.40

0.80

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Senescence

Senescence is the programmed death of plant cells or organs. A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants.

Leaf Abscission

A change in the balance of auxin and ethylene controls leaf abscission, the process that occurs in autumn when a leaf falls.

Ethylene

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Abscission of a maple leaf

0.5 mm

Protective layer

Stem

Abscission layer

Petiole

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Systems Biology and Hormone Interactions

Interactions between hormones and signal transduction pathways make it hard to predict how genetic manipulation will affect a plant.

Systems biology seeks a comprehensive understanding that permits modeling of plant functions.

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Responses to light are critical for plant success

Light cues many key events in plant growth and development.

Effects of light on plant morphology are called photomorphogenesis.

Plants detect not only presence of light but also its direction, intensity, and wavelength (color).

A graph called an action spectrum depicts relative response of a process to different wavelengths.

Action spectra are useful in studying any process that depends on light.

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Phototropic effectiveness

436 nm

1.0

0.8

0.6

0.4

0.2

0

400

450

500

550

600

650

700

Wavelength (nm)

(a) Action spectrum for blue-light phototropism

Light

Time = 0 min

Time = 90 min

(b) Coleoptile response to light colors

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