The mineral nutrient storage reserves in various parts of white spruce (Picea glauca) seeds and somatic embryos were investigated. Somatic embryos are produced in tissue culture from single cells or small groups of cells. These cells are induced to produce a callus, which is then stimulated to produce mature somatic embryos that are desiccated down to moisture content levels comparable to those of a mature dry seed. Morphological comparisons revealed that somatic and zygotic embryos are very similar. Somatic embryos of white spruce; however, were larger, had a flared arrangement of cotyledons, had more prominent suspensor regions, had intercellular spaces in the ground meristem tissue and had ground meristem cells that had divided in several planes of division. Using a wet ashing protocol, anion exchange resins and the molybdenum blue colourimetric reaction, the total levels of P and the amount of P bound to phytic acid were measured. Phytic acid (or phytate) is the major nutrient storage compound in seeds. Although differences were found on a dry weight basis, a single somatic and a single zygotic embryo had similar levels of P. Somatic embryos produced in different batches varied in their levels of phytic acid, but a somatic embryo could have similar levels of phytic acid as a zygotic embryo. The large female gametophyte contained 86% of the total P and 95% of the total phytic acid in a single seed. Electron microscopy and energy dispersive x-ray analysis found phytate-rich globoids in the procambium and ground meristem tissues of both types of embryos. Globoids contained high P, moderate K and Mg, and little if any Ca, Fe and Zn. Globoids were generally larger and more frequent in zygotic embryos. Globoids from the cotyledon procambium of zygotic embryos also contained moderate levels of Fe. Iron-rich particles (possible Fe-phytate deposits) were found in the protoderm, procambium and ground meristem of both types of embryos. These deposits contained high P and Fe, moderate K and Mg, and little if any Ca and Zn. Globoid and Fe-rich particle compositions were similar in both embryo types, but significantly higher Fe:P ratios were found in zygotic embryos. Atomic absorption spectroscopy was used to measure total K, Mg, Ca, Fe and Zn levels. Although differences were found on a dry weight basis, a single white spruce somatic or zygotic embryo contained similar levels of all these elements. The female gametophyte contained high levels of these elements and the seed coat contained considerable Ca. Potassium leakage during imbibition in germination medium revealed that a single somatic and zygotic embryo of white spruce leaked similar levels of K. Pretreatment of somatic embryos in a high relative humidity environment resulted in decreased potassium leakage by 80 and 120 min. of imbibition. The seed coat was found to reduce the amounts of K leaked. Surface cells in dry somatic and zygotic embryos were found to be wrinkled, but cells in zygotic embryos were more shrunken in appearance. During imbibition, cells became more turgid; but after 120 min. of imbibition, surface cells still showed signs of wrinkling. To date, this is the first major report of mineral nutrition in white spruce seeds and is the first comprehensive comparison of mineral nutrients in white spruce seeds and somatic embryos. These results may be useful in producing complete artificial white spruce seeds. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22968 |
| Date | 04 1900 |
| Creators | Reid, Daryl |
| Contributors | Lott, J. N. A., Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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