Phytoplankton in estuaries adapt to salinity stress by increasing the
content and unsaturation of the thylakoid lipid MGDG
Abstract
Life in estuaries, especially in surface waters, is a challenge,
particularly due to changes in salinity. Environmental changes
inevitably lead to acclimation or adaptation of phytoplankton in order
to survive. Since membranes are the first to perceive changes in the
environment, we focused on understanding how phytoplankton in estuaries
adapt to salinity stress through lipid remodeling. Since photosynthesis
is one of the most sensitive processes, we studied the response of
phytoplankton thylakoid membrane lipids to salinity stress. The study
was conducted in two estuaries with completely different environmental
characteristics. Apart from hydrology, estuaries also differ in
phytoplankton community compositions, nutrient status and temperature.
Here we show that estuarine phytoplankton, regardless of environmental
differences in the two estuaries studied, increase
monogalactosyldiacylglycerol (MGDG) content and unsaturation in response
to osmotic shock to protect photosynthetic machinery. This was
particularly pronounced at the lowest salinities when freshwater
phytoplankton encounter saline water and decreases with increasing
salinity. Our results also suggest that increased concentrations of
nitrogen nutrients have a positive effect on the increased unsaturation
of MGDG. Finally, we speculate that the freshwater green algae are the
major group responsible for the observed largest increased and content
of unsaturated MGDG at the lowest salinity.