In Arabidopsis, seed germination is regulated by light via phytochrome. Once phytochrome is activated by light in dark-imbibed seeds, expression of the gibberellin (GA) biosynthesis genes GA3oxl and GA3ox2 is upregulated, whereas the GA-deactivation gene GA3oxl is downregulated, resulting in an increase in concentrations of bioactive GAs. PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5) is a bHLH transcription factor that is involved in the regulation of GA biosynthesis and deactivation genes via phytochrome. Besides GA content, GA responsiveness also is modulated photo-reversibly via phytochrome in Arabidopsis seeds; in the absence of active phytochrome, more exogenous GA is necessary for the induction of germination of GA-deficient gal-3 mutant seeds. To understand the molecular mechanisms underlying phytochrome-regulation of GA responsiveness, we set out to identify phytochrome/PIL5-regulated genes in gal-3 mutant seeds using microarray analysis. We found that genes encoding DELLA proteins, negative regulators of the GA response pathway, are direct targets of PIL5, and that they contribute to altering GA responsiveness under varying light conditions. In addition, experiments using ga2ox2 mutants seeds and 2,2-dimethylGA_4, which is resistant to deactivation by GA2ox, indicated that elevated GA2ox2 expression in the dark also contributes to decreasing apparent sensitivity to exogenous GA_4.