LIGHT-REGULATED MODIFICATION AND NUCLEAR TRANSLOCATION OF CYTOSOLIC G-BOX BINDING-FACTORS IN PARSLEY

Functional cell-free systems may be excellent tools with which to inve stigate light-dependent signal transduction mechanisms in plants. By e vacuolation of parsley protoplasts and subsequent silicon oil gradient centrifugation of lysed evacuolated protoplasts, we obtained a highly pure and concentrated plasma membrane-containing cytosol. Using GT- a nd G-box DNA elements, we were able to demonstrate a specific localiza tion of a pool of G-box binding activity and factors (GBFs) but not on e of GT-box binding activity in this cytosolic fraction. The DNA bindi ng activity of the cytosolic GBFs is modulated in vivo as well as in v itro by light and phosphorylation/dephosphorylation activities. The re gulation of cytosolic G-box binding activity by irradiation with conti nuous white light and phosphorylation correlates with a light-modulate d transport of GBFs to the nucleus. This was shown by a GBF-antibody c otranslocation assay in permeabilized, cell-free evacuolated parsley p rotoplasts. We propose that a light-regulated subcellular displacement of cytosolic GBFs to the nucleus may be an important step in the sign al transduction pathway coupling photoreception to light-dependent gen e expression.