VARIATIONS IN THE CHLOROPLAST ULTRASTRUCTURE IN IN VITRO-CULTURED HYPERICUM SPP. PLANTS

D. Koleva, T. Ganeva, M. Stefanova

Abstract: Genus Hypericum comprises more than 480 species. Some of them have unique therapeutical properties, others are endemic or endangered. These features make the species appropriate objects for biotechnological manipulations. In vitro conditions considerably affect organogenesis and hystogenesis of plants subjected to micropropagation. Structural organization of the plastid apparatus in the leaf mesophyll of in vitro-cultured plants is an indicator for evaluation of the regeneration potential of the explants. The subject of the present study is the chloroplast ultrastructure of 7 in vitro-cultured Hypericum species – H. perforatum, H. humifusum, H. kalmianum, H. annulatum, H. tomentosum, H. pulchrum and H. rumeliacum. The aim is to analyze the morphological diversity of these vital for the process of regeneration cell compartments. TEM-analysis allows us to identify the differences among species at subcellular level of organization in correlation to the in vitro conditions. The morphological diversity of chloroplast structure manifests as altered plastid shape, organization of the internal membrane system, and starch content. The chloroplast shape of H. perforatum, H. annulatum, and H. pulchrum is elongated, which is typical for in vivo chloroplast. These species also are characterized with properly-structured thylakoid system. However, the grana height, the amount of stromal thylakolds, and the spatial orientation of the entire membrane system can vary. Signs
of thylakoid destruction are observed in H. humifusum, H. kalmianum, H. tomentosum, and H. rumeliacum. Only three in vitrocultured species (H. perforatum, H. annulatum and H. rumeliacum) develop chloroplasts with large amount of starch. The results show that the chloroplasts in H. annulatum have the most proper structure while the H. tomentosum chloroplasts are the most atypical. The great morphological variability in the organization of the plastid apparatus in Hypericum species reveals autonomous structural response of each of them to the in vitro conditions despite their genetic similarity.

Keywords: chloroplast ultrastructure; Hypericum sp.; in vitro; transmission electron microscopy

Date published: 2017-09-12