THE SYNERGISTIC EFFECT OF CARBON CONCENTRATION AND HIGH-TEMPERATURE ON LIPID-PEROXIDATION IN PERIDINIUM GATUNENSE

Lipid peroxidation in Peridinium samples taken from two different dept hs in Lake Kinneret fluctuated throughout the spring with an overall i ncreasing trend. Samples from 0.5 and 5 m showed a similar peroxidatio n pattern, which was maximal after the fall off in algal biomass. The rapid decline in Peridinium biomass coincided with ambient lake temper atures of 21-23 degrees C. Fatty acid composition profiles were simila r at both depths, although after the peak of the bloom, a significant increase in polyunsaturated fatty acids and oleic acid was only found at 0.5 m, together with a decrease in the percentage of polyunsaturate d fatty acids. These effects were related to ambient light stress rath er than a result of lipid peroxidation. Lake samples taken at differen t periods of the bloom and incubated at various temperatures showed di fferential peroxidation. Higher temperatures caused increased lipid pe roxidation, but this appeared to be dependent on the sampling period. Samples withdrawn from the lake at the beginning of the bloom showed l ittle peroxidation after a 5 day incubation at 14 degrees C, room temp erature (25 degrees C) or ambient lake temperature (16 degrees C) comp ared to mid-bloom samples in which there was a significant increase in peroxidation when they were incubated at room temperature (25 degrees C) or ambient lake temperature (22 degrees C). Incubation at 14 degre es C inhibited peroxidation; however, samples from mid-bloom again sho wed enhanced peroxidation compared with those from the beginning of th e bloom. These in situ results suggested a relationship between temper ature, another environmental variable during the bloom and lipid perox idation in Peridinium. As total dissolved inorganic carbon (DIG) conce ntrations fall significantly during the progress of the bloom and repr esent an important source of environmental stress, laboratory experime nts were established to investigate the synergistic effect of temperat ure and carbon nutrition on lipid peroxidation in Peridinium cultures. Increased temperature alone caused a slight increase in lipid peroxid ation, but this was greatly augmented by carbon limitation. Although c arbon limitation induced increased catalase activity, at higher temper atures activity declined after 48 h, allowing for the substantial incr ease in lipid peroxidation.