Transcript levels of two adjacent chloroplast genes during mustard (Sinapis alba L.) seedling development are under differential temporal and light control.

Transcript levels of two plastid genes were investigated during early seedling development of mustard (Sinapis alba L.) until 96 h after sowing. The two genes, which are closely linked and have the same polarity, are the psbA gene encoding the Mr 32-35000 herbicide-binding QB-protein of photosystem II and the trnK gene encoding plastid tRNA(Lys) (UUU) and potentially an intron-derived maturase-related protein. By using Northern and dot blot hybridization techniques with sensitive RNA probes, the 1.2 kb psbA transcript was found to be present in low amounts during the initial phase of seed germination. Thereafter, it increases in concentration both in light- and dark-grown seedlings until approximately 48 h after sowing. A further increase in psbA transcript concentration during the subsequent phase until 96 h was observed in light-grown, but not in dark-grown seedlings. The 2.8 kb trnK transcript is one to two orders of magnitude less abundant than the psbA transcript throughout the time period investigated. The concentration of this transcript is light-independent and shows a transient peak level at around 48 h, i.e. at the onset of light-enhanced accumulation of the psbA transcript.