Roles of in vitro plantlet age and growing period in the phenolic constituent yields of acclimatized Hypericum polyanthemum

The influences of culture period on growth, plant survival rate and content of phenolic compounds were investigated in vitro and in acclimatized field-grown plants of Hypericum polyanthemum. The growth kinetics of micropropagated plantlets cultured in MS modified medium and the concomitant transference to ex vitro conditions showed that cultures achieved maximum biomass and yield of bioactive compounds after 12 weeks of in vitro growth, with field-grown plants displaying the same survival pattern. Differences in yield among plants cultured in vitro for 8 and 12 weeks that were acclimatized and followed over two years showed that the physiological age of the in vitro cultures influenced biomass production. However, benzopyrans and total phenolic compounds (TPC) contents did not vary significantly, with the exception of the 5-hydroxy-6-isobutyryl-7-methoxy-2,2-dimethyl-benzopyran (HP3) concentration in the reproductive parts, which was higher in the plants grown in vitro for 12 weeks over the two years of the study. All analyzed plant parts from the spring harvest accumulated lower benzopyran levels than plants harvested after 18 weeks of growth in both treatments, except for the levels of 6-isobutyryl-5,7-dimethoxy-2,2-dimethyl-benzopyran (HP1) and 7-hydroxy-6-isobutyryl-5-methoxy-2,2-dimethyl-benzopyran (HP2) in the new vegetative parts of the plants, which did not vary. The concentration of TPC, which was detected at low levels in the old vegetative parts in both treatments, was not altered in other plant parts. The information provided by this work will help structure plant growth and collection periods designed to optimize the yield of each required bioactive metabolite.