Imbibition of white spruce seeds and somatic embryos: A study of morphological chances in an environmental scanning electron microscope and potassiumleakage

Potassium leakage and morphological changes during imbibition of white spru ce [Picea glauca (Moench) Voss] seeds and somatic embryos were investigated . A single desiccated somatic embryo; a single somatic embryo exposed to a high relative humidity environment for 2 d, and a single dry zygotic embryo leaked similar amounts of potassium over a 120-min period of imbibition in liquid germination medium. A seed without a seed coat leaked two and eight rimes more potassium than a single whole seed and a single zygotic embryo, respectively. Nearly 50% of the potassium leaked for all tissues was leake d within the first 20 min of imbibition. Exposure of somatic embryos to an environment with high relative humidity resulted in a reduction in the perc entage of potassium leaked after 80 and 120 min to levels equivalent to tho se for zygotic embryos. Using an environmental scanning electron microscope , we found that desiccated somatic embryos and dry zygotic embryos had wrin kled surface cells, with cells in the surface of zygotic embryos being more shrunken in appearance. Imbibition of both types of embryos in water resul ted in turgid surface cells after 2 h. Imbibition in liquid germination med ium did not cause much hydration of surface cells, which still had wrinkled appearances after 2 h. Finally: imbibition on filter paper on semisolidifi ed germination medium resulted in slower hydration of somatic and zygotic e mbryos. Cells near the medium appeared hydrated while cotyledon surface cel ls furthest from the medium resembled cells in desiccated embryos.