Pyrolysis mass spectrometry of developmental stages of maize somatic embryos

The diversity in biopolymers such as polysaccharides, (poly)phenols, nucleic acids and lipids in the developmental stages of two types of histologically dilferent somatic embryos of maize was investigated, using in-source pyrolysis low voltage electron impact mass spectrometry (PyMS) and the data were compared with those obtained for zygotic embryos. The first type of somatic embryo is attached to callus tissue and shows the same histo-differentiation characteristics as zygotic embryos. The second type grows from clusters of cells in liquid culture and its shoot meristem is blocked in development (Emons & Kieft 1991). In-source pyrolysis low voltage electron impact mass spectrometry shows that during callus initiation from young zygotic embryos the relative abundances of di- and triglycerides decrease, but increase again after establishment of the embryogenic callus. During callus initiation mass peaks for ferulic acid appear. The embryogenic cell clusters contain more pentosans and hexosans than the non-embryogenic elongated cells. In the globular stage, the hexosans increase. At the ovoid stage, when the first cells with vascular thickenings are observed in the sections, which are brightly fluorescent and can be stained with phloroglucinol, mass peaks for lignin are observed in the mass spectrum. The mass spectra of the developmental stages of somatic embryos grown attached to callus are quite comparable to those of zygotic embryos. Both structures contain far less phenolics, no lignin-like polyphenols, and a much higher amount of polysaccharides than the single somatic embryos.