RT-PCR analysis of HaGAS , HaCS , and FDPS gene expression in different developmental trichome stages. (a) Cross section of a sunflower capitulum showing young florets in the centre and older florets at the margin of the capitulum. (b) Micrographs of florets in differently developed trichome stages, as found in the capitulum. (c) Semi-quantitative RT-PCR experiments for identification of secretory active trichome stages. Ubiquitin was used as internal standard and loading control; FDPS: cDNA amplification of the expressed farnesyl diphosphate synthase gene; HaGAS: amplicons for H. annuus germacrene A synthases. HaCS: amplicons for H. annuus cadinene synthase.