Quantitative seasonal variation in mitochondrial ultrastructure of mesophyll cells ofDiapensia lapponica L. with reference to some effects of fixative osmolality

Summary Seasonal changes in the mitochondrial ultrastructure were examined in palisade parenchyma cells of a tuft-formingDiapensia lapponica L. collected at monthly intervals in Northern Finland. Quantitative analyses to measure volume and surface densities were conducted during different periods of growth (stages of growth, acclimation, winter period and deacclimation) in the annual cycle.The volume density was highest in the summer and lowest in the spring; the difference was significant with both fixatives used GA and GA/FA. The largest membrane area (the mitochondrial outer membrane and the cristal membranes together) was observed in the summer and autumn, and was significantly less in the winter and spring. This correlated with fewer mitochondria in the spring and a smaller number of cristae in the winter and spring. In the material fixed in GA/FA the distribution of length/width ratios of mitochondria was relatively uniform in all seasons. However, the mitochondrial ultrastructure had the most varied appearance during the winter. Hypertonie GA/FA solution did not cause significant differences either in the ultrastructure or the volume and surface densities of the mitochondria.Abbreviations GA glutaraldehyde - GA/FA glutaraldehyde/formaldehyde