Mineral nutrition in White Spruce ( Picea glauca [Moench] Voss) seeds and somatic embryos; II. EDX analysis of globoids and Fe-rich particles

Abstract

The elemental compositions of globoids and Fe-rich particles were investigated in white spruce ( Picea glauca [Moench] Voss) somatic embryos, zygotic embryos and female gametophytes using energy dispersive X-ray analysis. Globoids, phytate deposits in seed protein bodies, were found throughout the female gametophyte of seeds and in the ground meristem and procambium from all regions of both somatic and zygotic embryos. Iron-rich particles, believed to be Fe-associated phytate deposits in seed proplastids, were found throughout the female gametophyte of seeds and in the protoderm, ground meristem, and procambium from all regions of both somatic and zygotic embryos. Globoids in somatic and zygotic embryos ranged from 0.5–3.0 μm in diameter, but globoids typically ranged from 1.5–52.0 μm in diameter in somatic embryos and from 2.0–3.0 μm in diameter in zygotic embryos. Globoids in female gametophyte tissue ranged from 0.5–6.0 μm in diameter. All Fe-rich particles studied from somatic embryos and from seeds ranged from 0.14–0.25 μm in diameter. Globoids in somatic embryos and seeds contained high P, moderate K and Mg with occasional traces of Fe and little if any Ca and Zn. Globoids in the zygotic embryo cotyledon procambium tissue also contained moderate levels of Fe and had significantly higher Fe:P ratios, which were not found in any other regions in seeds or in somatic embryos. Iron-rich particles in somatic embryos and seeds contained high P and Fe, moderate K and Mg, and little if any Ca and Zn. Typically, spectra of Fe-rich particles in somatic embryos had P peaks higher than Fe peaks and spectra of Fe-rich particles in seeds had P peaks lower than Fe peaks. Overall, the composition of globoids and Fe-rich particles in somatic embryos and zygotic embryos were very similar with only minimal differences found.