Abstract
Sterol profiles of microalgae and their change with environmental conditions are of great interest in ecological food web research and taxonomic studies alike. Here, we investigated effects of light intensity and phosphorus supply on the sterol content of phytoplankton and assessed potential interactive effects of these important environmental factors on the sterol composition of algae. We identified sterol contents of four common phytoplankton genera, Scenedesmus, Chlamydomonas, Cryptomonas and Cyclotella, and analysed the change in sterol content with varying light intensities in both a high-phosphorus and a low-phosphorus approach. Sterol contents increased significantly with increasing light in three out of four species. Phosphorus-limitation reversed the change of sterol content with light intensity, i.e., sterol content decreased with increasing light at low phosphorus supply. Generally sterol contents were lower in low-phosphorus cultures. In conclusion, both light and phosphorus conditions strongly affect the sterol composition of algae and hence should be considered in ecological and taxonomic studies investigating the biochemical composition of algae. Data suggest a possible sterol limitation of growth and reproduction of herbivorous crustacean zooplankton during summer when high light intensities and low phosphorus supply decrease sterol contents of algae.
Highlights
Sterols are important structural and functional molecules in eukaryotic cells
In contrast to animals, which predominantly contain cholesterol, plants and algae contain a great diversity of different phytosterols. These sterols differ in their number and position of double bonds in the ring structure of the tetracyclic molecule and in the structure of the side chain. Until now it is unclear if this variety in sterol composition entails an advantage for plants and if individual sterols play specific roles in plant cell metabolism [2]
Statistical analyses of the effects of light and phosphorus supply on the content of each of these three sterols in S. quadricauda revealed significant interactions (Table 1), i.e. in the high-P treatment the sterol content increased with light intensity but decreased in the low-P treatment
Summary
Sterols are important structural and functional molecules in eukaryotic cells. They are involved in the regulation of membrane fluidity, signal transduction and modulation of the activity of membrane-bound enzymes [1]. In contrast to animals, which predominantly contain cholesterol, plants and algae contain a great diversity of different phytosterols These sterols differ in their number and position of double bonds in the ring structure of the tetracyclic molecule and in the structure of the side chain. Grandmougin-Ferjani et al [4] revealed that cholesterol and stigmasterol are able to stimulate the H+ pump of the ATPase in higher plant plasma membranes. These examples suggest that specific sterols may have particular functions in plant cells apart from their general role as structural components in cell membranes
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