Re: How do plants live in salt water?

The only submerged ocean plants in the current Plant Kingdom are the seagrasses. They don't live deep enough to be without light. They live in shallow waters usually near the coasts. Other photosynthetic ocean organisms, algae and some bacteria, are now in separate Kingdoms.

By definition aquatic plants have adapted to living partly or totally submerged. While a terrestrial plant will often die when the soil is waterlogged due to lack of oxygen for the roots, aquatic plants will not.

Seagrass salt tolerance is due to their maintaining a lower water potential in their cells than the surrounding salt water. They do this by accumulating sodium in the cell vacuoles. Recently, scientists discovered a salt tolerance gene that codes for a transport protein that carries sodium into the vacuole. The salt tolerance gene has been transferred into tomato plants thus making them salt tolerant.

References

Marine Seagrasses: Flowering Plants Adapted To Sea Water

Gene Makes Tomatoes Tolerate Salt

Re: Ocean plants and roots

Planting seagrass continues re-emergence of Tampa Bay

Seagrass Meadows

Salt Tolerance Gene