Temporal Pattern of Gene Expression in Cotyledons of Mustard (Sinapis alba L.) Seedlings

The time course of appearance of competence to phytochrome (P_fr) was studied in cotyledons of mustard (Sinapis alba L.) with regard to the light-mediated accumulation of mRNAs encoding for SSU, CAB and the 23 kDa protein of the oxygen evolving complex of photosystem II (OEC). For each gene family a specific starting point of P_fr-induced mRNA accumulation was observed (SSU: 42 h; CAB: 36 h; OEC: 30 h). An increase of SSU-mRNA levels can be detected 24 h after sowing in dark-grown seedlings whereas for OEC the time points for the increase of mRNA are the same whether the seedlings are kept in darkness or induced by light via P_fr. For all gene families a responsiveness to P_fr (coupling point) could be demonstrated before the starting points. The coupling points are also gene specific (SSU: ca. 12 h; CAB and 23 kDa peptide of OEC: ca. 24 h). The responsiveness to light before the starting point indicates that the light-induced signal must be stored.