Effects of visible light - photoreceptor action

Depending on their chemical nature, chromophores undergo different modes of light-induced molecular transformation. As can be seen in Table 8.2, the transformation modes include trans-cis isomerization, charge transfer, and energy transfer. 

The phosphorylation at Ser-598 exerts an accelerating effect on the association of PIF3 and NDPK2 and the phosphorylation of PKSl (phytochrome kinase substrate 1). The latter is a protein that is complexed to the Pr state of the phytochrome and is released from the photoactivated Pjj. state after phosphorylation to give downstream signals through a kinase cascade [39]. Recall that a kinase is an enzyme that catalyzes the phosphorylation of a substrate, here a protein. 

In conclusion, the light-induced isomerization of carbon-carbon double bonds in the chromophore causes a series of conformational changes within the two domains of the phytochrome. These changes trigger the association of signal transducer proteins with the phytochrome and allow phosphorylation and phosphate transfer at various sites. These are key steps initializing the downstream of processes that eventually result in transcriptional regulation. 

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