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Morphomechanical changes appearing during embryonic development of Scardinius erythrophthalmus L. were followed. Upon complete egg hydration, the yolk together with the embryo was found to occupy about 30% of egg volume, the perivitelline space making up the remaining 70%. The embryonic disc, and the embryo later on, were always located laterally in the egg. As in many other cyprinids, the developing eggs of S. erythrophthalmus contain no strucutral lipids in the form of droplets. At the mid-point of embryogenesis, the yolk begins to divide; as a result, a vitellar diverticulum – elongating as the development continues – appears under the caudal part of the fast growing embryo. After hatching, the diverticulum is transformed into the posterior part of the body cavity. Until hatching, the S. erythrophtalmus embryos lack melanophores both in the skin and in the eyes.
To understand the molecular mechanism controlling in vitro plant morphogenesis, a culture system enabling induction of alternative morphogenic pathways (somatic embryogenesis, SE; shoot organogenesis, ORG) in a well defined population of somatic cells is needed. Arabidopsis is the most useful model plant for genomic studies, but a system in which SE or ORG can be induced alternatively in the same type of explant has not been proposed. Immature zygotic embryos (IZEs) of Arabidopsis provide the only explants with embryogenic potential, and have been recommended for studying mechanisms of SE induced in vitro. This study was aimed at defining culture conditions promoting induction of alternative morphogenic pathways: shoot ORG in IZE explants. The established protocol involves pretreatment of IZE explants with liquid auxin-rich callus induction (CIM) medium, followed by subculture on solid cytokinin-rich shoot induction medium (SIM). The method enables efficient shoot induction in Columbia (Col-0) and Wassilewskija (Ws), genotypes commonly used in molecular studies. During 3 weeks of culture up to 90% of Col-0 and 70% of Ws explants regenerated shoots via an indirect morphogenic pathway. We analyzed the qRT-PCR expression patterns of the LEC (LEC1, LEC2 and FUS3) genes, the key regulators of Arabidopsis embryogenesis, in the IZE explants induced to promote shoot ORG. The sharp decline of LEC expression on SIM medium confirmed that culture of Arabidopsis IZE explants enables experimental manipulation of the morphogenic response of somatic cells. A scheme illustrating various in vitro morphogenic responses of IZEs in relation to hormonal treatment is presented.
The study-compared effect of cytokinins on morphogenesis and ploidy of plants regenerated in vitro from explants of ‘Stanola F1’, ATZ and ATM pepper seeds. The aim of defining the morphogenetic potential of the studied genotypes, half-seed explants consisting the proximal part of the hypocotyl and radicle were put onto the MS medium containing BAP (5.0 mg.dm-3), 2iP (2.5 mg.dm-3), ZEA (2.5 mg.dm-3), TDZ (1.5 mg.dm-3), while MS medium without cytokinins constituted the control. After the initiation period, explants were transferred onto the medium without cytokinins. The effect of the growth regulators to the morphogenetic response of explants was estimated based on the number of explants on which adventitious buds and shoots were developing. The cytokinins applied did not show a significant effect on the development of adventitious buds on pepper explants.
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