The Role of Phytohormones in the Induction of Somatic Embryogenesis in Pinus sibirica and Larix sibirica

The contents of auxin (indole-3-acetic acid, IAA), cytokinins, and abscisic acid (ABA) were determined in explants (megagametophyte and embryo), proliferating embryonal-suspensor mass (ESM), and non-embryogenic callus of Pinus sibirica and Larix sibirica. Furthermore, the localization of hormones in the cells was studied with immunohistochemical analysis. It was shown that the formation of embryogenic cultures in both species is associated with the content of phytohormones and their localization in cells. In L. sibirica the content of IAA in ESM was about 100 times higher than in non-embryogenic calli. At the same time, a low ABA content was characteristic of embryogenic cultures. Non-embryogenic callus contains an increased content of cytokinins and ABA. The transition of somatic cells to the path of embryogenic development is characterized by elongation of cells, their asymmetric division, and localization of IAA at one of the ends of elongated cells. Non-embryogenic callus consisted of isodiametric, actively dividing cells.