Response of trehalose, its degrading enzyme, sucrose, and floridoside/isofloridoside under abiotic stresses in Gracilariopsis lemaneiformis (Rhodophyta)

Compatible solutes, including trehalose, sucrose, and floridoside/isofloridoside, are involved in acclimation to abiotic stresses in red algae. However, the contributions of these carbohydrates, especially trehalose and sucrose, to the stress response are still unclear. In the present study, the accumulation of these carbohydrates and the gene expression and activity of trehalase (the only degrading enzyme of trehalose) were studied under three stress conditions in the seaweed Gracilariopsis lemaneiformis. Under heat stress, trehalase activity was decreased to 0.38- and 0.46-fold at 24 and 48 h, respectively, whereas trehalose and floridoside/isofloridoside were significantly accumulated. Under salt stress, levels of trehalose and its degrading enzyme were almost unchanged; however, the floridoside amount increased between 12 and 24 h, and isofloridoside only exhibited a 1.44-fold increase at 48 h. Under drought stress, the transcriptional level and activity of trehalase were markedly upregulated with a maximum 4.36-fold increase (at 3 h) and 2.37-fold increase (at 48 h), respectively; trehalose levels remained unchanged; floridoside was significantly inhibited, and isofloridoside was almost unchanged except for a slight decrease at 24 h. In conclusion, trehalose and floridoside/isofloridoside were stimulated by heat stress; floridoside accumulation was triggered under hyperosmotic conditions; the mRNA abundance and activity of trehalase were activated by the drought treatment. However, sucrose made no contribution to abiotic stress tolerance in G. lemaneiformis.