How are some plants salt tolerant?

It is possible for plants to be more adapted to living near salt water. Many beach grasses, along with mangrove trees, kind of "sweat" the salt out of their systems. the next time oyu go to the beach, rub some dune grass. does any white powder come up on your finers? this is salt. Im not sure of the actual systems the plants use to get rid of the salts, though.