Photoresponse Mechanisms in Plants and Animals

Although photosynthesis and vision are the most obvious uses of light by living organisms from simple bacteria to the highest forms of life, there are 

Colour vision relies on three pigments of different absorption spectra, B, G and R. Wavelength A in nm/100 

It is not surprising that the detailed mechanism of such processes is very difficult to establish. It is known however that the molecule phytochrome is involved in many cases this molecule can exist in two different forms which are called Pr (red phytochrome) and Pfr (far-red phytochrome) which are interconvertible by the action of light 

Depending on the wavelength distribution of light, a photostationary state can be established between Pr and Pfr. 

The Pfr isomer formed photochemically is the biologically active molecule, its mode(s) of action being complex dark reactions which are not fully understood at the present time. 

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