Content and immunohistochemical localization of hormones during in vitro somatic embryogenesis in long-term proliferating Larix sibirica cultures

We carried out immunoassay of plant hormones [indoleacetic acid (IAA), cytokinins and abscisic acid (ABA)] in the extracts from explants (megagametophytes and embryos) and from four long-term proliferating embryogenic cell lines of Larix sibirica. Immunohistochemical detection of hormones has also been performed at the stage of initiation of somatic embryogenesis and in embryogenic cultures during the process of somatic embryo morphogenesis. During induction of somatic embryogenesis in tissue culture, the first stage of cell development is manifested in their elongation and polarization. Immunohistochemical analysis of hormones showed localization of IAA at one pole of elongated cells of L. sibirica. The polarity of embryogenic structure development persisted later on. The difference has been shown in the content of hormones between the explants and embryogenic cultures. High level of hormones was detected in the cell line (Cl4), distinguished by great number of globular embryos and high capacity for their maturation. Hybrid line Cl5 (L. sibirica × L. sukaszewii) formed very short suspensor, accumulated higher amount of ABA in the head of somatic embryos (SEs) than did other lines, while SEs of this cell line did not maturate. Cl6 was characterized by low plant hormones content in proliferating embryogenic cultures and low yield of mature somatic embryos.