Abstract
Desiccation and high salinity are two abiotic stressors that are related in terms of their effect on water homeostasis within cells. The success of certain aeroterrestrial microalgae is influenced by their ability to cope with desiccation, and in some cases, high salinity. The microalgae of the Stichococcus clade are ubiquitous in terrestrial habitats and are known to withstand desiccation and salinity stress by accumulating secondary metabolites. Nevertheless, it remains unclear if those two related stressors have a synergistic effect. Hence, we studied the effect of salinity on desiccation on various representative taxa within the Stichococcus clade. The results showed that in contrast to other Stichococcus taxa, Pseudostichococcus was able to recover fully after desiccation, with and without salinity stress. This observation was connected to elevated proline production under salinity stress and higher proline:sorbitol ratio in Pseudostichococcus to the other strains tested. In the other taxa, increasing salinity reduced their ability to withstand desiccation. This might have severe effects on microalgae in (semi)arid regions, where salinization of soils is an increasing threat also for agriculture. The results encourage further research to be done on the possible applications of this genus in salinity bioremediation, as it seems to be comparable to other halotolerant green algae used for this purpose.
Highlights
Microalgae inhabiting terrestrial environments must cope with irregular water availability and, depending on the specific habitat, significant salt stress
Salt stress is related to dehydration, but is defined as “physiological drought” [1], where osmotic stress disrupts normal cellular ion concentrations, even if water in the environment is plentiful
There has been extensive research done on the adaptive mechanisms in terrestrial microalgae to desiccation [3,4,5,6] and salt stress [7,8,9]
Summary
Microalgae inhabiting terrestrial environments must cope with irregular water availability and, depending on the specific habitat, significant salt stress. The ecological success of terrestrial algae may be attributed to their ability to withstand repeated and extended drought-rewetting cycles, as well as UV and temperature stress. Salt stress is related to dehydration, but is defined as “physiological drought” [1], where osmotic stress disrupts normal cellular ion concentrations, even if water in the environment is plentiful. Dissociated Na+ and Cl− ions are cytotoxic in high concentrations [2]. There has been extensive research done on the adaptive mechanisms in terrestrial microalgae to desiccation [3,4,5,6] and salt stress [7,8,9]. The focus on these two stressors in combination has been primarily in crop plants and marine seaweeds [10,11,12,13]
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