EARLY CHANGES IN GENE-EXPRESSION DURING THE TRANSITION FROM VEGETATIVE TO GENERATIVE GROWTH IN THE LONG-DAY PLANT SINAPIS-ALBA

Changes in gene expression during flower formation were studied in the long-day plant Sinapis alba. The day length dependence was exploited to synchronize flower formation in a large population of mustard plants. After an inductive light treatment, apices were harvested after different lengths of time, and changes in gene expression were analyzed. Two major groups of genes were identified whose expression was affected during flower formation. Transcripts of the first group (group I) were present at low concentration in the apex of noninduced plants. They began to accumulate strongly after the end of the inductive light period. They reached a maximum 2 days to 10 days after flower induction and then declined slowly. Transcripts of the second group of genes (group II) could be detected for the first time 10 days after flower induction. Within a very short time, these transcripts accumulated dramatically and reached a maximum 15 days after flower induction before beginning to decline. They dropped beyond the limit of detection before the flower reached maturity.