Plant growth regulator levels during maturation of larch somatic embryos

Abstract

The profile of various hormones was assessed during maturation of somatic embryos of hybrid larch ( Larix kaempferi (Lamb.) Carriere × L. decidua Miller). Auxins (2,4-dichlorophenoxyacetic acid, 2,4-D; indole-3-acetic acid, IAA; indole-3-butyric acid, IBA; indole-3-acetic-aspartate, IAasp), cytokinins (benzyl aminopurine, BAP; isopentyladenine, iP; isopentyladenosine, iPA; zeatin, Z; zeatin riboside, ZR) and abscisic acid (ABA; abscisic acid glucosyl ester, ABA-GE) were measured in somatic embryos maturing on a medium supplemented with 60 μM ABA and 1 μM IBA. These were compared to embryos and megagametophytes dissected from mature hybrid larch seed. Plant growth regulators were extracted in methanol, purified, fractionated by high pressure liquid chromatography (HPLC) and quantified by enzyme-linked immunosorbent assay (ELISA). In somatic embryos, ABA and ABA-GE rose steadily to 225 and 26 pmol·embryo –1, respectively. In zygotic embryos and megagametophytes, abscisic acid levels were orders of magnitude lower. IBA concentration in the first week of somatic embryo maturation was 816 fmol·embryo –1, but dropped to below detection levels within a week. IAA and IAasp concentrations rose over the course of development. Final concentration of IAA in somatic embryos (731 fmol·embryo –1) was comparable to that found in zygotic embryos (877 fmol·embryo –1). Cytokinins such as Z and ZR fluctuated at low concentrations (0.1–5.2 fmol·embryo –1 range). With the exception of week 5, when levels of iP and iPA reached 20–30 fmol·embryo –1, levels of these substances were generally within the 0.1–6.5 fmol·embryo –1 range. Cytokinin concentrations were similar to those of mature zygotic embryos.