Seasonal fluctuations in storage lipids in the cushion plant Diapensia lapponica, growing in Northern Finland (70°N 27°E), were studied by microscopy and chemical analysis. Lipid bodies in the mesophyll cells were stained with Sudan Black for quantitative observation by light microscope. Electron microscope observations were made using aldehyde prefixed and osmium tetroxide postfixed sections of leaf blades. Thin layer and gas capillary chromatographic techniques were used to analyse total lipids and total fatty acids in green shoots of Diapensia. Free sugars and starch were extracted separately and determined by the anthrone method.
A mesophyll cell was characterized by a large lipid body (storage lipid) in summer but by several small spherules in winter. Total surface area of the cross-sectioned lipid globules was at its lowest from April to September; the maximal value was in March. The amount of total lipids in the leafy tops of D. lapponica was 91–200 mg g-1 dry weight. Values were lowest at the end of June, when the total carbohydrate level was at its highest. Accordingly, the decrease in the total lipid level in the early growing season, when new leaves were developing, can be attributed primarily to the increase in the level of carbohydrates, particularly starch. The amount of total fatty acids varied from 21 to 30 mg g-1 dry weight. The level increased in the early growing season and remained elevated throughout the summer. Like the total lipids, the total fatty acids are derived from structurally different parts of the sclerophyllous leaves, including the well-developed cuticle and epicuticular wax layer. The discrepancies in the results obtained from microscopic and chemical analyses are discussed.