We have been using the classical model long-day (LD) plant Lolium temulentum Ceres, which can flower after a single inductive LD treatment, to study the floral transition in grasses. Plants of L. temulentum have been grown in short days (SD), transferred to LD and apices isolated after SD and a number of LD treatments, before being examined by SEM. We have used these observations to focus on the changes which occur in gene expression during the first 6LD. RNA has been isolated from meristems and cDNA-AFLP used to compare gene expression between SD and LD treatments. A number of florally enhanced cDNA fragments were identified including one with homology to the flowering time gene CONSTANS (CO) of Arabidopsis thaliana. When this cDNA was mapped in L. perenne (perennial ryegrass), it mapped close to the major quantitative trait locus for heading date. However we do not believe the sequence is the Lolium CO-ortholog since it is much more similar to an Arabidopsis CO-like sequence than to CO itself and does not appear to exhibit a daily rhythm as observed for CO and some other CO-like sequences. In addition, and rather intriguingly, the gene seems to be most highly expressed in the outer most leaf sheath although we are also able to detect RNA in the meristem. Recently to help us understand the function of this CO-like gene, we have identified a T-DNA insertion in the A. thaliana equivalent of the gene but have yet to identify a phenotype.