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Stomata detached from the epidermis of common dayflower (Commelina communis) were treated with saturating photon fluxes of red light. After 2 hours, the same stomata, under the background of red light, were also illuminated with blue light.

Which one of the following statements regarding opening of stomatal apertures is true?

Correct option is C

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Explanation:

Stomatal Opening Mechanism: Role of Red and Blue Light

• Stomata regulate gas exchange and transpiration by adjusting their aperture size in response to environmental cues.
• Light is a key factor in stomatal opening, with both red and blue light contributing to this process through different mechanisms.

Effect of Red Light on Stomatal Opening

·       Red light plays a role in stomatal opening by driving photosynthesis in guard cells, leading to ATP production.

·       The increase in ATP activates proton pumps (H⁺-ATPases) in the guard cell membrane, which causes K⁺ ions to enter, leading to water influx and stomatal opening.

·       However, red light alone reaches a saturation level, beyond which further red light does not increase stomatal aperture.

Effect of Blue Light on Stomatal Opening

·       Blue light directly stimulates phototropins (Phot1 and Phot2), which are blue light receptors in guard cells.

·       Activation of phototropins leads to a stronger activation of H⁺-ATPases, allowing

greater ion uptake (K⁺, Cl⁻) into guard cells.

·       This results in a larger stomatal opening than red light alone.

Statement C is correct Since the stomata were already exposed to saturating red light, they were partially open. Adding blue light further increases the aperture due to its independent mechanism via phototropins.