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Galactic Travler
the differential sensitivity of Photo Receptors
Light Quality Effects on Plant's Physiology and Morphology
UV-B 280-300/315/320 mn (putuative UV-B photoreceptor)
The effects can be separated by UV-B dosage. Low doses induce UV-B specic photomorphogenetic and developmental responses. High doses in more general stress signal transduction.
UV-A 320 – 390 nm (cryptochromes, phototropins)
Phototropism, light-induced opening of stomata, chloroplast migration in response to
changes in light intensity and solar tracking by leaves of certain plant species.
Contributes to maximising photosynthetic potential in weak light and preventing
damage to the photosynthetic apparatus in excess light.
Blue (B) 390–500 nm (cryptochromes, phototropins)
Phototropism, chloroplast relocation, stem elongation (de-etiolation),
photoperiod-dependent flowering induction, resetting the circadian oscillator.d
Maximises photosynthetic potential in weak light and prevents damage to the
photosynthetic apparatus in excess light. Controls stomatal opening at low light levels
(<15 μmol m−2 s−1 ). Upregulates genes that encode key enzymes in the Calvin cycle.
Act as a catalytic wavelength for obtaining high quantum yields of photosynthesis and
activates respiration. Strong blue light activates the incorporation of carbon in amino
acids, that is it inhibits starch formation in leaf chloroplasts and increases the
biosynthesis of proteins.
Yellow 580 – 600 nm (cryptochromes, phytochromes)
Downregulates genes coding for key enzymes in the Calvin cycle.e Suppresses growth of
some greenhouse plants.
Red (R) 600 – 700 nm (R-absorbing phytochrome form Pr)
Stem elongation (de-etiolation). Entrainment of the circadian clock. Downregulation of
genes encoding for key enzymes in the Calvin cycle. Activates the photosynthetic
reaction centres PSI and PSII.l In many species, low-fluence red light induces seed
germination. Prolonged exposure to red light eliminates the possibility of the
enhancement of protein biosynthesis by blue light.
Far-red (FR) 700 – 800 nm (FR-absorbing phytochrome
form Pfr)
Often cancels the effects of preceding red light. In many species, inhibits seed
germination. Stem elongation (de-etiolation).
B : R
Crucial for photosynthetic activity.
B : FR
Seed germination, seedling establishment, shade-avoidance response, floral induction.
Note:
Many light responses are mediated by the coordinated action of more than one photoreceptor.
