Effect of light intensity on the fatty acid composition of dinoflagellates symbiotic with hermatypic corals

Abstract

We examined the effects of varying light intensity on fatty acid composition in symbiotic dinoflagellates (SD) isolated from hermatypic corals Millepora intricata , Pocillopora damicornis , Seriatopora caliendrum , Seriatopora hystrix and Stylophora pistillata . The corals were subjected to 95%, 30%, 8% and 2% of incident photosynthetic active radiation (PAR). Irradiance had a significant effect on fatty acid composition of polar lipids and triacylglycerols. SD showed substantial changes in the proportion of 16:0 as a response to variation in PAR. During adaptation to high light, the percentage of 16:0 increased in polar lipids and triacylglycerols. Additionally, the percentage of 14:0, 16:1(n-7) increased in triacylglycerols. Thus, high light conditions lead to an increase in storage products. Polar lipids of SD adapted to low levels of PAR had greater concentrations of 18:4(n-3), 20:5(n-3), 18:5(n-3) and 22:5(n-6) which are commonly involved in the formation of thylakoid membranes. Conversely, the amounts of 20:4(n-6) and 22:6(n-3) increased with increasing irradiance, suggesting an association with photosynthesis. The elevation in percentages of 18:4(n-3), 20:5(n-3) and 18:5(n-3) during exposure to low light was accompanied by an increase in chlorophyll a content in the SD cells. Light-dependent changes in fatty acid composition are probably due to the correlation of activity of photosystems with processes of production and desaturation of fatty acids.