Abscisic acid and its influence on development of the embryonal root cap, storage product and secondary metabolite accumulation in hybrid larch somatic embryos

Abstract

Somatic embryos of Larix × leptoeuropaea were grown on modified MSG media with 60 μM abscisic acid (ABA). These were compared to control embryos raised on the same medium without ABA. Transmission electron microscopy demonstrated that zonation of polyphenol production as well as presence of extracellular mucilage was markedly different in embryos raised with and without ABA. Idioblasts were found in subepidermal and pith regions of hypocotyls and among the subepidermal cells of cotyledons in embryos matured on ABA, but not in embryos matured without ABA. The embryonal root caps of ABA-treated embryos had substantial deposition of lipids and proteins in both the column and inner pericolumn regions, but not in the outer layer of the pericolumn. Control embryos showed no accumulation of proteins or lipids, but an increase in polyphenol accumulation, which had spread to the epidermal and sub-epidermal layers of the cotyledons and hypocotyl. Starch accumulation was similar over the course of development in embryos treated with or without ABA. Using gas chromatography-selected reaction monitoring mass spectrometry, it was shown that concentrations of ABA averaged 186 ± 17 μg g⁻¹ dry weight (DW) in embryos raised on medium supplemented with this plant growth regulator, versus an average concentration of 55 ± 19 μg g⁻¹ DW in embryos raised in the absence of ABA. No difference in ABA concentration was found between the root cap and the rest of ABA-treated embryos.