Q.37 Stomatal opening is stimulated by
- Red-light
- Yellow light
- Blue light
- Green light
Blue light is the primary stimulus for stomatal opening. This occurs through specific photoreceptors in guard cells that trigger ion uptake and water influx.
Question Analysis
Stomatal opening regulates gas exchange and photosynthesis in plants. Among the options—red light, yellow light, blue light, and green light—blue light (around 400-500 nm) is most effective.
Option Breakdown
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Red light: Promotes opening indirectly via photosynthesis in mesophyll cells, raising guard cell turgor. It enhances blue light effects but alone is less potent at low intensities.
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Yellow light: Minimal impact; lies outside key absorption spectra for stomatal photoreceptors or chlorophyll. No significant stimulation observed.
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Blue light: Directly activates phototropins (phot1/phot2) in guard cells, pumping H+ out via ATPases. This hyperpolarizes the membrane, drives K+ influx, and causes osmosis-driven swelling.
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Green light: Often inhibits blue light-induced opening or has negligible effect; guard cells reflect much of it.
Correct Answer: Blue light.
Stomatal opening stimulated by blue light drives plant photosynthesis and water regulation. This process, key for life sciences students, involves guard cells responding to specific wavelengths for optimal CO2 uptake.
Light Wavelength Effects
Blue light triggers rapid opening through phototropin kinases, activating H+-ATPases. Red light supports via photosynthetic signals but requires higher intensity. Yellow and green wavelengths fail to stimulate effectively, as they evade photoreceptor activation.
Light Type Effect on Stomata Mechanism Red Moderate opening Photosynthesis-driven turgor Yellow Negligible Poor absorption Blue Strong opening Phototropin signaling Green Inhibitory/None Reflection by cells Biochemical Pathway
Phototropins autophosphorylate under blue light, inhibiting anion channels like SLAC1. This leads to K+ accumulation, water entry, and pore widening—essential for exams like CSIR NET.
Blue light ensures early morning opening, synergizing with red for full-day function. Disruptions affect crop yields, highlighting its agricultural relevance.
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