ULTRASTRUCTURE OF EMBRYONIC PHASEOLUS VULGARIS L. AXES DURING ANHYDROBIOSIS AND THE DEVELOPMENT OF MITOCHONDRIA DURING EARLY GERMINATION

Scope of Study. This dissertation is composed of two related studies. The first concerns the ultrastructure of the dormant, dry embryonic axis of the green bean, Phaseolus vulgaris L. In this study, an anhydrous technique was used to prepare the tissue for electron microscopy, and general observations of the ultrastructural status of the tissue were made. In the second study, development of the mitochondria present in the dry seed was followed. Respiratory activity, increase in the fresh weight, and the effect of KCN, SHAM, DNP and KCN + SHAM were determined for the intact axes during the first 16 h of germination. In addition, tissue was prepared for electron microscopy, and stereological analyis was performed at 3, 6 and 16 h to determine whether mitochondrial volume, numbers and or size were changing during this period. In addition, tissue that was inbibed in cold water for 30 min was prepared for electon microscopy.;Three phases of oxygen consumption characterize early respiratory development. There is an initial imbibition phase, a lag phase and a phase of rapidly increasing respiration and fresh weight that accompanies elongation of the radicle. Sensitivity to KCN declines during early germination, while SHAM alone has little effect on O(,2) consumption. Combining KCN and SHAM was initially effective, but this effect declined after 6 h. It is thought that this indicates increasing activity of other oxidases in the tissue. DNP-stimulated O(,2) consumption indicates that the electron transport system is adequate to carry all electrons generated by the tricarboxylic acid cycle. Stereological analysis of mitochondrial volume, number and size indicates that these organelles are not changing in general morphology during this period. The area of the inner mitochondrial membrane does not appear to change during this period, and mitochondria in 16 h germinated embryos look like those of embryos imbibed 30 min at 4(DEGREES)C. Thus it appears that the population of mitochondria present at the beginning of germination increases in activity. Mitochondrial profiles are often seen in clusters, and there are indications that at this time in the development of the green bean mitochodrial morphology is complex and that single mitochondrial profiles may not represent individual mitochondria.;Findings and Conclusions. In the dry embryonic axis of P. vulgaris the cells are shrunken with folded cell walls and compactly arranged cellular components. Lipid droplets line the cell margins, plastids and mitochondria are aggregated and irregular ovoid protein bodies are numerous. The protein bodies are often sheathed in layers of ribosomes and associated membrane. The nucleus contains distinct marginal heterochromatin and nucleoli. The cytoplasm is packed with ribosomes. Cellular membranes appear in negative contrast as electron dense and transparent lines adjacent to one another. An explanation for this appearance is advanced based upon biophysical considerations of lipid-protein interaction and the effects of drying upon membranes.