Na( (+) )/K( (+) )-ATPase regulates the K( (+) )/Na( (+) ) homeostasis in the intertidal macroalgae, Neoporphyra haitanensis, in response to salt stress

In plants under hypersaline stress, the main transporter that extrudes sodium ions (Na( (+) )) is the Na( (+) )/H( (+) ) antiporter SOS1. Different from land plants, the intertidal macroalgae, Neopyropia/Neoporphyra contains an animal-type Na( (+) )/K( (+) )-ATPase as well as the SOS1 system. However, the contribution of Na( (+) )/K( (+) )-ATPase to the K( (+) )/Na( (+) ) homeostasis of intertidal macroalgae remains unclear. In this study, we analyzed the function of Na( (+) )/K( (+) )-ATPase in the response of Neoporphyra haitanensis to salt stress from the perspective of ion transport dynamics. Both the transcript level of NhNKA2 and enzyme activity of Na( (+) )/K( (+) )-ATPase increased in the early response of N. haitanensis thalli to hypersaline stress. Addition of ouabain, an inhibitor of Na( (+) )/K( (+) )-ATPase, resulted in Na( (+) ) accumulation in the cells, severe K( (+) ) leakage from the thalli, and then remarkably disturbed the K( (+) )/Na( (+) ) homeostasis in N. haitanensis thalli. This disruption might induce a significant decrease in photosynthesis and a severe oxidative damage in thalli. Accordingly, these results suggested that the important role of Na( (+) )/K( (+) )-ATPase in the resistance of intertidal macroalgae to hypersaline stress, and shed light on the diversity of K( (+) )/Na( (+) ) homeostasis maintenance mechanisms in plants.