Sulfate assimilation pathway is highly responsive to changes in environment, but the mechanisms of such regulation are only slowly beginning to unravel. Here we show evidence that PHYTOCHROME AND FLOWERING TIME 1 (PFT1) may be another component of the sulfate assimilation regulatory circuit. Transcriptional regulation by light of the key enzyme of sulfate assimilation, adenosine 5'phosphosulfate (APS) reductase, is disturbed in pft1-2 mutants. PFT1, however, affects also APS reductase enzyme activity, flux through the sulfate assimilation pathway and accumulation of glutathione. In addition, our data suggest a possible interplay of PFT1 with another transcription factor, HY5, in regulation of APS reductase by light.