The contents and distribution of hormones in the proliferative embryogenic cultures of Larix sibirica

The localization and endogenous content of phytohormones (indole-3-acetic acid, IAA; cytokinins; and abscisic acid, ABA) were studied in proliferating embryogenic cell lines (CLs) of Larix sibirica. Cell elongation, polarization, and polar localization of IAA at one pole of elongated cells were observed during the initiation of embryogenic cultures. In proliferating CLs, intense immunofluorescent staining of the embryonal globule for IAA, zeatin, and ABA was observed, whereas embryonal tubes of the suspensor did not contain hormones. In young, actively proliferating cell lines, IAA content ranged from 495 to 2380 ng g−1 DW, total cytokinins from 54 to 166 ng g−1 DW, and ABA was very low (9–24 ng g−1 DW). During long-term proliferation (11–14 years) or even after only 3 years in some cell lines, IAA increased to 3687 ng g−1 DW, total cytokinins changed only slightly, whereas ABA increased to 970 ng g−1 DW. ABA above 300 ng g−1 DW, accompanied by high IAA, was associated with reduced or complete loss of somatic embryo maturation and plantlet regeneration capacity.