Plant senses

Question 1

Explain the role of phototropins and auxin in plants bending toward blue light

Answer 1

phototropins in sensory cells are proteins used to detect blue light, and once they do they cause the sensory cell to make and release the hormone auxin. Auxin is then transported to other areas of the plant where it binds to receptors, mainly the shady areas. This ramps up the proton pumps which creates an electrochemical gradient and lowers the pH outside the cell, activates expansins, relaxes cell wall, and allows cell to swell with water, and therefore causes cell elongation. This uneven distribution of auxin results in the shady side of a plant to experience more cell elongation, and causes a plant to move toward sunlight.

Question 2

Staring with the binding of auxin to receptors, explain how cells elongate under the acid-growth
hypothesis (include proton pumps, electrochemical potentials, expansin, hydrogen bonds, K+,
cellulose microfibrils, and water potential for full credit)

Answer 2

The binding of auxin to receptors turns on proton pumps which then pump protons out of the cell and therefore lowering the pH outside the cell which triggers the activation of expansins. Expansins act like little scissors cutting hydrogen bonds that are holding the cellulose microfibrils together and this process relaxes the cell wall. Ions (K=) flow into the cell through the electrochemical gradient lowering the water potential, which then causes the cell to swell with water and the turbot pressure causes the cell to elongate now that the cell wall is relaxed.

Question 3

Name three reasons why the stomata will open and close.

Answer 3

Phototropins detect blue light and cause stomata to open (during the day)
Phototropins do not detect blue light and therefore the stomata stay closed (at night)
ABA is produced by roots and causes guard cells to close (drought stress response)

Question 4

How do the stomata open and close? Be sure to explain the role of proton pumps,
electrochemical gradients, and water potential in the opening and closing of stomata.

Answer 4

Protons are pumped out by proton pumps when Phototropins are struck by blue light, forming an electrochemical gradient, ions enter (K+ and Cl-), water potential lowers, water enters, cells swell and guard cell “opens”
When ABA binds to receptors on guard cells, proton pumping stops, K+ exits, water potential increases, water exits, cells shrink and guard cell “closes.”

Question 5

Name two hormones that affect the opening and closing of stomata.

Answer 5

ABA and phytohormones (ethylene and jasmonic acid)

Question 6

Which conformation of phytochrome causes lettuce seeds to germinate.

Answer 6

the Pfr conformation
(The Pr conformation is hit by red light, causing a shape change to Pfr which activates the protein ultimately causing germination)

Question 7

Why would a lettuce seed not want to germinate if it was getting far-red light (~735nm)?

Answer 7

Because far-red light causes the Pfr conformation to change to Pr. This inactivates protein and therefore no germination occurs.

Question 8

The length of time a plant is exposed to certain wavelengths of light can inhibit or promote flowering. If you exposed a short-day plant to 15 hours of dark, but flashed it for a few minutes with Far-red light, would it germinate? What is the far-red light mimicking?

Answer 8

The far-red light is mimicking shady conditions, which would cause a short-day plant to germinate and bloom because it is used to shorter days and longer nights

Question 9

Auxin has many roles in a plant. How does it act differently in a branch growing toward the light
versus a root growing downward?

Answer 9

Auxin in the stem is going to move to the shady side of the stem to cause cell elongation and push the growth of the stem towards the sun. Auxin in the root is going to inhibit cell growth on the bottom of the root (exact opposite of stem) to force it downward

Question 10

If you wanted more rose flowers on your rose bush, why would you remove the apical meristem
(include auxin in your answer)?

Answer 10

Removing the apical meristem will allow the lateral buds to begin to grow new branches. Auxin promotes this cell division, development of vascular cambium, and differentiation of xylem and phloem

Question 11

apical dominance maintains g row the in main stem where the lateral buds remain dormant until apical meristem is removed

Question 12

thigmotropism

Answer 12

Touch-bending
Tendrils will attach to various structures, holding the vine up

Question 13

senescence

Answer 13

Regulated process of aging and eventual death
—>cell walls are degraded, starch is broken down to sugar, toxins removed/ destroyed, and pigments and aromas are produced
(Flowers fading)