FR730 nm

R660 nm

l300

l400

l500

l600

l700

l800

Wavelength (nm)

0 -

0.2 -

0.4 -

0.6 -

0.8 -

R

Pr

ϕ = 0.85

k1, 660 nmk2, 660 nm

PfrPfr

Phytochromes - R/FR photoreceptors

at equilibrium:

d[Pfr]/dt = 0 = k1λ[Pr] - k2λ[Pfr]

[Pfr]/[Ptot] = ϕ = k1λ / (k1λ + k2λ)

FR730 nm

R660 nm

l300

l400

l500

l600

l700

l800

Wavelength (nm)

0 -

0.2 -

0.4 -

0.6 -

0.8 -

FR

PrPr

Pfr

ϕ = 0.03

k1, 720 nmk2, 720 nm

Phytochromes - R/FR photoreceptors

Yet: phyA exhibits strongest effect (growth inhibition) in FR

Distribution of the position of the maximum in the action spectrum

How to construct a far-red light receptor from a red light receptor

X Y

Slightly extended network

I

∅ ∅

IIZ

∅

Low fluence rates

High fluence rates

Realization in planta

Different compartments

k1

k2

PrPn

frBinding of FHY1 Cn

fr

k2

k1

Pnr

k1

k2

Pfr