Influence of the Habitat Altitude on the (Proto)Hypericin and (Proto)Pseudohypericin Levels of Hypericum Plants from Crete

Environmental factors are known to influence strongly the accumulation of secondary metabolites in plant tissues. In a previous paper, we studied the contents of (pseudo)hypericin and its immediate precursors in wild populations of various Hypericum species on the island of Crete, Greece, in dependence on their developmental stage. In this Study, we investigated the effect of the habitat altitude on the total hypericins content of the plants, which is defined as the sum Of protohypericin, hypericin, protopseudohypericin and pseudohypericin. Taking into account our previous finding that the highest accumulation is found during the flowering period in June, we collected the aerial parts of spontaneously growing H. perforatum L., H. triquentrifolium Turra, H. empetrifolium Willd. and H. perfoliatum L. during that time frame at elevations between 100 and 600 m above sea level, however, bearing in mind the time lag in development with increasing altitude. HPLC analysis of the plant material, separated again into a flowers and a leaves/petioles fraction, revealed great differences in the total hypericin content in dependence on the altitude of the habitat. Specifically, a clear trend was revealed, showing an increase of the total hypericin content with increasing altitude. However, no changes could be observed in the ratio of hypericin to protohypericin and in that of pseudohypericin to protopseudohypericin. The habitats of the employed plants were again randomly distributed all over Crete. It is proposed that higher light intensities accompanied by enhanced UV-B radiation and lower air temperature might be responsible for the increasing levels of total hypericins with increasing altitude.