If the plant is not salt-water adapted, it will experience outward osmosis and will experience dehydration as the plant cells lose water to the outside environment and shrink. This is also called plasmolysis. When there are greater water molecules inside the cell relative to the outside(where there is a concentration of salt), outward osmosis occurs across the gradient from high to low concentration. This results in water leaving the cells of the plant and it will dehydrate.
Plants absorb water from the soil through their roots by osmosis. Salinity is bad for osmosis and can even make the plant lose water back into the soil, making them look dry and wilted.