HEADING DATE 1 (Hd1) is a zinc finger transcription factor, central in the photoperiodic flowering network. Hd1 operates as a repressor of flowering under long days but reverts to a promoter of flowering under short days. How this dual function is organized at the proteomic level is still unknown. Here, we have used MS to interrogate the proteome of hd1 mutants and wild type plants under long and short day conditions, and we identified differential abundance of proteins involved in cell wall metabolism.