Bluelight Receptors

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Lecture 26
Blue-light Receptors
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Examples of responses mediated by blue-light
receptors
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Relationship between direction of growth and
unequal incident light
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Phototropism a blue light response
Phototropism directional growth toward the
light in fungi, ferns and
higher plants
Wild type
Phototropic bending only growing organs
Mutant
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Darwins experiments on phototropism
How can we distinguish specific responses to blue
light from red/far-red light?

• In specific blue-light responses, blue light
  cannot be replaced by a red-light
• treatment.
• There is no red/far-red reversibility.
• Many blue-light responses share a characteristic
  action spectrum.

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Action spectrum for blue light-stimulated
phototropism
Three-finger fine structure between 400
and 500 nm
Examples - inhibition of hypocotyl
elongation - stomatal movements
This shape of action spectrum is NOT observed in
spectra for responses to light mediated by
photosynthesis, phytochromes, or other
photoreceptors.
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Photoreceptors
Cryptochromes (1 and 2) Phototropins (1 and
2) Others?
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Phenotype of the hy4 mutant
Blue-light inhibits hypocotyl elongation
Elongated hypocotyl in hy4
? The HY4 gene encodes a blue light
photoreceptor, CRYPTOCHROME 1 (CRY1)
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Blue light stimulates the accumulation of
anthocyanin and inhibits stem elongation
CRY1 over- expressing line
CRY1 over- expressing line
Evidence for role of CRY1 in blue light-mediated
signaling
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Phenotypes of cry2 mutant
Col
cry2
cyr2 is late flowering under long day conditions
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Functions of the cryptochromes
Regulation of seedling de-etiolation and
elongation growth Regulation of flowering
time Co-action with phytochromes The
cryptochromes are NOT involved in phototropic
curvature.
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Identification of the photoreceptor(s)mediating
phototropism NPH1 Phototropin 1
(Complementation with WT gene)
The non-phototropic hypocotyl 1 mutant has a
defective phototropic response.
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Blue light regulates chloroplast movement inleaf
mesophyll cells (phototropins)
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Phototropins mediate blue light-dependentstomatal
opening
Light
Light
Dark
Light
Bean plant
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Functions of the phototropins
Phototropic curvature Chloroplast
movement Stomatal opening