Light intensity influences the glycerolipid remodeling of Gracilariopsis lemaneiformis in response to short-term high temperature stress

Abstract

Temperature and light are two pivotal environmental factors for the growth of marine photosynthetic organisms. While the responses of Gracilariopsis lemaneiformis to individual high temperature or light stress have been explored, our understanding of its combined stress responses remains limited. This study aimed to investigate the combined effects of short-term high temperature (33 °C, 8 h) and different light intensities, that is, low light (LL, 50 μmol photon m−2 s−1), medium light (ML, 150 μmol photon m−2 s−1), and high light (HL, 300 μmol photon m−2 s−1), on the physiological responses and lipid remodeling of G. lemaneiformis. Results demonstrated that short-term exposure to either high temperature or high light stress led to a reduction in maximum (Fv/Fm), effective photochemical efficiency (Fv'/Fm') and maximum relative electron transfer rate (rETRmax), and the combination of these stresses exerted a more pronounced inhibitory effect on photosystem II efficiency. Short-term exposure to heat stress led to an increase in superoxide dismutase (SOD) activity, as well as a rise in glutathione (GSH) and ascorbate (Asc) contents under LL, while the activities of antioxidant enzymes (SOD, peroxidase, and ascorbate peroxidase) and levels of non-enzymatic antioxidants (GSH and Asc) were reduced under ML and HL. Additionally, short-term heat stress induced the accumulations of phosphatidylcholine (PC), phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, sulfoquinovosyldiacylglycerol, and triacylglycerol (TAG) under LL, while heat-induced lipid accumulation decreased under ML and HL. Furthermore, heat stress increased the accumulation of saturated or unsaturated PC species under LL. Specifically, there was an increase in the levels of saturated or monounsaturated acyl chain–containing PC species, whereas the levels of polyunsaturated acyl chain-containing PC species declined under ML and HL. Correspondingly, a significant increase in TAG species with polyunsaturated acyl chains was observed, particularly under LL conditions, suggesting a potential lipid turnover between PC and TAG. These results showed that the lipid metabolic plasticity of G. lemaneiformis enabled it to rapidly adapt to fluctuating environmental conditions, and the light environment regulated its heat stress response.