Genotype-dependent response of St. Johǹ`s wort (Hypericum perforatum L.) shoot tips to cryogenic treatment: Effect of pre-culture conditions on post-thaw recovery

Cryopreservation of medicinal plants is an important tool for restoration of their potential to synthesize valuable secondary metabolites. Establishment of an efficient protocol requires detailed understanding of species/genotype-specific responses to changing external variables. The aim of this work was to study the genotype-dependent response of Hypericum perforatum L. shoot tips to different pre-cryogenic conditions. Shoot apices isolated from plants growing on the hormone-free medium and from clusters induced by addition of benzylaminopurine, were subjected to pre-culture using two agents (0.3M sucrose and 0.076μM abscisic acid) prior to cryopreservation. Although the genotypes represented the seed progeny of one mother plant, the results showed their different capability to withstand cryogenic treatment. The differences were apparent especially in case of plants cultivated on the hormone-free medium. The ability to recover depended also on the pre-culture agent, duration of the pre-culture period and under certain conditions also on interaction between benzylaminopurine and abscisic acid in the medium. The results are illustrated by anatomical alterations of the meristematic zones and adjacent leaf primordia. Long term exposure of cultures to benzylaminopurine resulted in the delay of abscisic acid effect during pre-culture step and thus impaired regeneration capability of shoot apices after cryopreservation.