Question

Which wavelength of light is primarily responsible for inducing the opening of stomata in plant leaves?

• A. Red light
• B. Blue light
• C. Green light
• D. Ultraviolet light

Hint:

The stomatal response to blue light is highly sensitive. Even low intensities of blue light superimposed on a background of red light can trigger rapid stomatal opening.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Stomatal opening regulates gas exchange and transpiration in plants. The guard cells surrounding the stomatal pore respond to environmental cues, particularly light, to coordinate stomatal movements with photosynthesis.

Step 2: Detailed Explanation:
- While both red and blue light can promote stomatal opening, blue light ($430\text{--}470 \text{ nm}$) is the primary and most effective wavelength for inducing stomatal opening.
- The molecular mechanism of blue-light-induced stomatal opening involves:
1. Photoreception: Blue light is absorbed by specific photoreceptors called phototropins (phot1 and phot2) located in the plasma membrane of guard cells.
2. Proton Pumping: Activated phototropins trigger a signaling cascade that activates plasma membrane $\text{H^+$-ATPases}. These pumps actively force protons ($\text{H}^+$) out of the guard cells, generating an inside-negative electrical potential across the membrane.
3. Ion Influx: This hyperpolarization drives the passive influx of potassium ($\text{K}^+$) ions through inward-rectifying channels. Malate and chloride ($\text{Cl}^-$) ions also accumulate to maintain charge neutrality.
4. Osmotic Swelling: The accumulation of these solutes lowers the osmotic potential ($\Psi_s$) inside the guard cells, drawing water inward. This increases turgor pressure, causing the guard cells to swell and open the stomatal pore.
- Red light promotes stomatal opening indirectly by driving photosynthesis in guard cell chloroplasts, which reduces internal $\text{CO}_2$ levels. However, blue light triggers a direct, highly sensitive signal transduction pathway.

Step 3: Final Answer:
The wavelength of light primarily responsible for stomatal opening is Blue light.