The blue light photoreceptor mutant cryptochrome1-304 (cry1-304) and Columbia wild-type 4 (col-4) of Arabidopsis thaliana were grown under white light and blue light,and in the dark.To study the difference in protein expression levelsbetween cry1-304 and col-4,a proteomic approach was applied based on 2-D gel electrophoresis.Twenty-one different protein spots were identified by matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry.The expression of four genes corresponding to four protein spots was analyzed by semiquantitative reverse transcriptionpolymerase chain reaction.We applied analytical procedures to study cry1-304 and col-4,and found that the differentially expressed proteins formed six clusters reflecting coregulation.This assessment was consistent with the known physiological responses of plants to light.