The  role  of  phytochrome in the
   de-etiolation ("greening") response.
<P>
<Li> Reception:  Light  activates a receptor molecule, a pigment called
phytochrome.
<Li> Transduction:  the phytochrome produces cGMP as a second messenger
that  activates  a  protein kinase; the phytochrome also increases
flow  of  Ca^2+  into  the  cytoplasm and activate another protein
kinase.
<Li> Response:  both  pathways  lead  to expression of genes to produce
proteins that function in the de-etiolation ("greening") response.