The synergistic effect of carbon concentration and high temperature on lipid peroxidation in Peridinium gatunense

Lipid peroxidation in Peridinium samples taken from two different depths in Lake Kinneret fluctuated throughout the spring with an overall increasing trend. Samples from 0.5 and 5 m showed a similar peroxidation pattern, which was maximal after the fall off in algal biomass. The rapid decline in Peridinium biomass coincided with ambient lake temperatures of 21-23 degrees C. Fatty acid composition profiles were similar 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 polyunsaturated fatty acids. These effects were related to ambient light stress rather than a result of lipid peroxidation. Lake samples taken at different periods of the bloom and incubated at various temperatures showed differential peroxidation. Higher temperatures caused increased lipid peroxidation, but this appeared to be dependent on the sampling period. Samples withdrawn from the lake at the beginning of the bloom showed little peroxidation after a 5 day incubation at 14 degrees C, room temperature (25 degrees C) or ambient lake temperature (16 degrees C) compared 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 degrees C inhibited peroxidation; however, samples from mid-bloom again showed enhanced peroxidation compared with those from the beginning of the bloom. These in situ results suggested a relationship between temperature, another environmental variable during the bloom and lipid peroxidation in Peridinium. As total dissolved inorganic carbon (DIG) concentrations fall significantly during the progress of the bloom and represent an important source of environmental stress, laboratory experiments were established to investigate the synergistic effect of temperature and carbon nutrition on lipid peroxidation in Peridinium cultures. Increased temperature alone caused a slight increase in lipid peroxidation, but this was greatly augmented by carbon limitation. Although carbon limitation induced increased catalase activity, at higher temperatures activity declined after 48 h, allowing for the substantial increase in lipid peroxidation.