Does salt water effect the sunflowers plant growth?

If you mean salt water as in an experiment, you have to remember that salt will dehydrate the plant by the process of osmosis. A formerly healthy plant, when given the salt water, will begin to wilt, have yellowing of the leaves and any further growth will be stunted.

If you mean growing sunflowers at a beach property, I can tell it to you straight. It can't be done unless you really, really protect the plant (greenhouse environment with filtered water and soil brought in from elsewhere). Like most annuals, sunflowers do not tolerate salt spray.