Chloroplast ultrastructure of Hypericum perforatum plants regenerated in vitro after cryopreservation

The ultrastructure of leaf mesophyll cells of in vitro cultured Hypericum perforatum L. plants regenerated after cryopreservation was studied. Electron microscopy analysis revealed that the chloroplasts in plants pretreated with abscisic acid and regenerated after cryopreservation were round, with increased amount of starch, rather small volume of the thylakoid system, and destroyed envelope. Plants pretreated with 0.3 M mannitol and cooled at rates of 0.1 or 0.3 A degrees C min(-1) possessed chloroplasts with high starch content that resulted in a reduction of a membrane system. However, the pretreatment with 0.3 M mannitol and cooling at a rate of 0.2 A degrees C min(-1) was the best as chloroplast ultrastructure resembled the controls regenerated without cryopreservation.