HPLC analysis of the seasonal and diurnal variation of iridoids in cultivars of Antirrhinum majus.

In this paper we show the seasonal and diurnal variation in the content of the four iridoids found in cultivars of Antirrhinum majus, antirrhinoside, antirrhide, 5-glucosyl-antirrhinoside and linarioside. The seasonal variation in total iridoid content showed a marked bimodal distribution with high total values (around 100mg/g dry matter) early and late in the season and a very low content of all iridoids coinciding with the onset of flowering at the beginning of August. The relative contribution of antirrhinoside was significantly higher before flowering than after bud break. The relative decrease in antirrhinoside was counteracted by an increase of antirrhide, which was significantly higher after the onset of flowering than before. This pattern indicates a change in biosynthesis, although no explanation can be given to the phenomenon. The diurnal variation showed a variation between 20 and 60mg/g dry weight, but there was no relation to light/darkness conditions, temperature patterns or water content. The analyses were performed by HPLC. The applied method has not previously been used in the quantification of iridoids, but was developed specifically for the analyses of cultivars of Antirrhinum majus. We have fully validated the method during its development. The limit of detection was calculated to 0.004mg/ml and the limit of quantification was 0.01mg/ml.