BIOL 117 Chapter 16

plant signal transduction

hormone binds to outside of receptor —> change in receptor —^{> reactions producing second messengers —}> ^{activation of cellular responses}

light, gravity, physical contact, water availability, and temperature

what are plant sensitive to changes in?

Every change comes from different hormonal signals in plants

true

2 plant light responses

photomorphogenesis and phototropic response

photomorphogenesis

non-directional development and tells seeds when to flower, seed germination, and biological clock

Phototropic response

directional development and compensates for the inability to move across landscape

Both light responses rely on light sensitive receptors (wavelength specific)

true

phytochrome

protein that contains red light sensitive to photopigments

phytochrome never change shape from red light

false

photomorphogenesis protein

phytochrome

photoperiod

how long each day plants are exposed to sunlight that controls flowering

phototropin

protein complex with blue light sensitive pigments

tip of plants

where are phototropins found in the plant?

gravitational response

negative response, grow away from pull

root cap

senses gravity

auxin

promotes cell growth

Thigmotropism

response to physical contact

Seed germination is induced by red light and inhibited by far-red light. What is responsible for this phenomenon?

Phytochrome changing its shape when exposed to red versus far-red light

Flowering would occur

If the following lighting pattern were applied to a short-day (long-night) plant, which response would you expect?

true

A phytochrome in the P_fr conformation has recently been exposed to red light (~660nm)

tip of the shoot

Where on the body of an adult plant would you find a phototropin receptor?

Cells on the illuminated side of a stem elongate more than cells on the shaded side.

Which of the following statements about phototropism is false?

Auxin release that travels down a single side of a plant’s stem.

Which of the following would initiate a plant’s phototrophic response?

root cap

If cells in the _____ are removed, roots will no longer respond to gravity

Expansin

What is the name of the enzyme that is directly responsible for breaking down cellulose in plant cell walls during the phototropic response?

Red/far red

To which wavelength of light are phytochrome receptors in plants sensitive?

Flowering would not occur

If the following lighting pattern were applied to a LONG-day (SHORT-night) plant, which response would you expect?

Blue

To which wavelength of light are phototropin receptors sensitive?