Investigating the mechanisms underlying the hyposaline tolerance of intertidal seaweed, Pyropia haitanensis
2020
Wang, Wenlei | Chen, Tianxiang | Xu, Yan | Xu, Kai | Xu, Yan | Ji, Dehua | Chen, Changsheng | Xie, Chaotian
Although intertidal macroalgae are highly tolerant to hyposaline stress, the underlying mechanisms remain poorly characterized. In this study, we investigated the effects of a short-term immersion in hyposaline conditions [5‰ (LSS_5) and 0‰ (LSS_0)] on the physiological characteristics and the transcriptome of Pyropia haitanensis. The hyposaline stress treatment caused more severe damages to the thalli than the hypersaline stress conditions. Decreased growth and energy metabolism may benefit the thalli by redirecting energy to specific stress responses under hyposaline stress. The reactive oxygen species production was lower under LSS_5 compared with LSS_0. Although superoxide dismutase activity and glutathione contents increased under the LSS_0 condition, the freshwater induced more severe oxidative damages. Moreover, P. haitanensis thalli rapidly excreted Na⁺, K⁺, and proline to achieve osmotic balance. However, K⁺ content of cells remained high when thalli were exposed to LSS_5, which is advantageous for the high photosynthesis rate of thalli. The mechanisms behind Na⁺ and K⁺ export and the osmolyte adjustments under hyposaline stress were distinct from hypersaline stress. Additionally, the upregulation of extensins might increase cell wall flexibility to maintain cell turgor pressure and act as a stress signal under LSS_5. The activation of heat shock proteins maintained the protein homeostasis under LSS_0, which may be a signature of the ability of Pyropia spp. to cope with several abiotic stresses in the intertidal zone. The present study paves the way for more detailed investigations of the mechanisms behind the hyposaline stress tolerance of intertidal seaweed.
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