Plastid- and light-regulated expression of the spinach PsaD gene in transgenic tobacco requires sequences downstream of the transcription start site, sand promoter sequences alone are not sufficient to respond to these stimuli. The spinach PsaD mRNA level in transgenic tobacco is still plastid- and light-responsive when the expression of the intron-containing transcription unit is driven by the 35S RNA CaMV promoter indicating that PsaD contains (a) gene-internal control element(s). If the genomic PsaD sequence in the latter construct was replaced by the cDNA, a constitutive expression of the PsaD transcript level was observed. It is concluded that the intron sequence contributes to the plastid- and light-dependent expression of the spinach PsaD gene.