The role of phytochrome in the de-etiolation ("greening") response.
Light activates a receptor molecule, a pigment called phytochrome.
the phytochrome produces cGMP as a second messenger
that activates a protein kinase;
the phytochrome also increases flow of Ca2+
into the cytoplasm and activate another protein kinase.
both pathways lead to expression of genes to produce proteins that function in the
de-etiolation ("greening") response.