| Pecan, Carya illinoinensis (Wangenh), is the most economically important nut tree crop indigenous to North America. Somatic embryogenesis has been shown to be a plant tissue culture technique with potential applications for mass clonal propagation, genetic transformation, and use in studies in embryo development. In pecan, a highly repetitive pecan somatic embryogenic system has been developed. However, pecan somatic embryos, like many other somatic embryos, convert at a low rate. Several amendments to the growth condition of pecan somatic embryos (cold treatment and desiccation) have been shown to enhance maturation/germination-related morphological development. However, the biochemical changes that are associated with these maturation enhancement treatments have not been studied yet. Furthermore, an understanding of the morphological, physiological and biochemical changes taking place during pecan zygotic embryo development will be helpful in understanding the effect of maturation enhancement treatments on the development of pecan somatic embryos. Based on the distinct developmental changes in the characters listed above, pecan zygotic embryo development stages can be divided into (a) histodifferentiation, (b) cotyledon, (c) maturation, and (d) post-abscission stages. During pecan zygotic embryo development, several insoluble proteins were evident after the onset of ‘maturation stage’. However, soluble proteins were first expressed during the early cotyledon stage and continued to be present in maturing embryos. Some of these proteins disappeared during the post-abscission stage, potentially those that are germination-related. When the somatic embryos were subjected to conversion enhancement treatments of cold and desiccation, the total protein content per unit embryo weight increased to a level similar to zygotic embryos. The same treatment resulted in an increase in triglyceride content although total triglyceride levels remained well below that found in zygotic embryo. A quantitative change in the classes of fatty acids occurred following conversion treatments, with the mole percentage of fatty acids becoming more similar to that found in zygotic embryos. |
