The fatty acid composition of phospholipids and the contents of docosahexaenoic acid (DHA)-containing diacyl phosphatidylcholine and diacyl phosphatidylethanolamine molecular species were determined from brains of five fresh-water fish species from a boreal region adapted to 5°C, five fresh-water fish species from a temperate region acclimated to 5°C, five fresh-water fish species from a temperate region acclimated to 20°C, and three fresh water fish species from a subtropic region adapted to 25-26°C, as well as six mammalian species and seven bird species. There was little difference in DHA levels of fish brains from the different thermal environments; mammalian and bird brain phospholipids contained a few percentage points less DHA than those of the fish investigated. Molecular species of 22:6͞ 22:6, 22:6͞20:5, 22:6͞20:4, 16:0͞22:6, 18:0͞22:6, and 18:1͞22:6 were identified from all brain probes, and 16:0͞22:6, 18:0͞22:6, and 18:1͞22:6 were the dominating species. Cold-water fish brains were rich in 18:1͞22:6 diacyl phosphatidylethanolamine (and, to a lesser degree, in diacyl phosphatidylcholine), and its level decreased with increasing environmental͞body temperature. The ratio of 18:0͞22:6 to 16:0͞22:6 phosphatidylcholine and phosphatidylethanolamine was inversely related to body temperature. Phospholipid vesicles from brains of cold-acclimated fish were more fluid, as assessed by using a 1,6-diphenyl-1,3,5-hexatriene fluorescent probe, than those from bird brains, but the fluidities were almost equal at the respective body temperatures. It is concluded that the relative amounts of these molecular species and their ratios to each other are the major factors contributing to the maintenance of proper fluidity relationships throughout the evolutionary chain as well as helping to maintain important brain functions such as signal transduction and membrane permeability.

No abstract

The compositions of lipid classes as well as the molecular species composition of subclasses (diacyl, alkylacyl, and alkenylacyl forms) of choline and ethanolamine phosphoglycerides in marine amphipod crustaceans, Gammarus spp., collected in the Baltic Sea at 8 and 15 degrees C, were studied in relation to environmental temperature. The structural order of phospholipid multibilayers was also determined. Environmental temperature had little effect on fatty acid composition. The level of some polyunsaturated fatty acids, such as 20:4, even increased in choline and ethanolamine phosphoglycerides at 15 degrees C. Ethanolamine phosphoglycerides were rich in alkenylacyl forms, especially in crustaceans collected at 15 degrees C. The accumulation of sn-1 monoenic, sn-2 polyenic diacyl, alkyl, and alkenylacyl phosphatidylethanolamines and diacyl phosphatidylcholines was observed at 8 degrees C. The phospholipid vesicles of crustaceans collected at 8 degrees C were more disordered than expected compared to those obtained from animals collected at 15 degrees C. It was concluded that, in addition to variations in the levels of sn-1 monoenic and sn-2 polyenic phospholipid molecular species with temperature, ethanolamine plasmalogens may play a role in controlling membrane biophysical properties in marine amphipod crustaceans.

The development of a filamentous, nitrogen-fixing cyanobacterial bloom was followed during July-ugust 1990 in a stratified basin in the central Gulf of Finland, altic Sea . Hydrography, dissolved inorganic, particulate and total nutrients, chlorophyll a, alkaline phosphatase activity, 32 P04-uptake and phytoplankton species were measured . The study period was characterized by wind-induced mixing events, followed by marked nutrient pulses and plankton community responses . Phosphate uptake was highest throughout the study period in the size fraction dominated by bacteria and picocyanobacteria ( 2 am) and the proportion of uptake in the size fraction 2-10 pm remained low (2-6%) . Higher phosphate turnover times were observed in a community showing signs of enhanced heterotrophic activity. The bloom of filamentous, nitrogen-fixing cyanobacteria phanizomenon flos-aquae was promoted by a nutrient pulse with an inorganic nutrient ratio (DIN :DIP) of 15 . The results show that the quality, frequency and magnitude of the physically forced nutrient pulses have an important role in determining the relative share of the different modes of phosphorus utilization and hence in determining the cyanobacterial bloom intensity and species composition in the altic Sea .

No abstract