In vitro morphogenetic responses from obligatory apomictic Taraxacum belorussicum Val. N. Tikhom seedlings explants

Taraxacum belorussicum Val. N. Tikhom, a poorly known and obligatory apomictic species, is an attractive plant material for studying the embryological, genetic and molecular mechanisms of apomixis. This work aims to obtain an efficient protocol for Taraxacum belorussicum regeneration. Four types of explants (cotyledons, hypocotyls, meristems and roots) that were taken from 2-weeks-old seedlings were used for in vitro cultures, and a fast and efficient protocol of T. belorussicum regeneration was obtained. Various 1/2 MS-based media containing IAA (5.71 mu M), TDZ (4.54 mu M) and PSK (100 nM) were chosen to assess the morphogenetic abilities of selected T. belorussicum explants. Studies on the role of PSK were done in three independent experiments, where the most significant factors were always light and darkness. All explants produced callus by the third day of culture and adventitious shoots after 7 days, although in an asynchronous indirect manner, and with different intensities for all explant types. The most preferred medium culture for hypocotyl, cotyledon and meristem explants was 1/2 MS + TDZ, and 1/2 MS + IAA + TDZ + PSK for roots which were the only explant sensitive to PSK. A short darkness pretreatment (8 days) in PSK medium was found suitable to enhance organogenesis. Secondary organogenesis was observed for regenerated plants on meristem explants from the 1/2 MS + IAA + TDZ + PSK medium. A weak somatic embryogenesis was observed for hypocotyl and cotyledon explants from 1/2 MS + IAA + TDZ and 1/2 MS + IAA + TDZ + PSK media. Histological and scanning electron microscope images (SEM) of T. belorussicum confirmed indirect organogenesis and somatic embryogenesis. Plant material treated with aniline blue solution revealed the presence of callose in the cell walls of cotyledon and hypocotyl explants. The presence of extracellular matrix (ECM) and heterogenic structure of callus was also verified by scanning electron microscopy and light microscopy, confirming the high morphogenetic ability of T. belorussicum. Key message An efficient regeneration protocol for Taraxacum belorussicum, the obligatory apomict, was obtained. Application of PSK revealed the significance of light and darkness as a key factor in the morphogenetic response. A short darkness pretreatment (8 days) in PSK medium was found suitable to enhance organogenesis. Histological and scanning electron microscope images confirmed indirect organogenesis and somatic embryogenesis presence. The protocol can enhance the knowledge about this species in studying the embryological, genetic and molecular mechanisms of apomixis.