The salt glands of some mangrove plants remove excess salt using ion transporters that help create a concentrated sodium solution.

Mangroves are shrubs or small trees that are found in coastal areas where ordinary plants cannot survive. One difficulty they face in their environment is the different salinity of the tides that come in and out from the coast. 

When the mangrove’s root tissues are exposed to salt water, the concentration of salt in the vessels of the root is lower than the concentration of salt in the water surrounding the plant. This concentration gradient would tend to drive salt ions across the plant tissue’s membranes into its cells. However, mangroves have various salt tolerance mechanisms that vary with species: they can exclude salt, accumulate salt, and/or excrete salt. Plants that exclude salt prevent it from entering the membranes of their roots. In other plants that do end up containing excess salt, some  accumulate it into older leaves so it can be shed with the leaves. Others excrete salt, in much higher concentration than seawater, through s on their leaves. 

Research on the mechanism of salt excretion has led to the hypothesis that a network of channels and pumps moves salt (specifically, sodium ions) between plant cells to the glands that eventually excrete the excess salt. The cytoplasm (inner material) of each plant cell is connected by channels in the cell membranes, enabling cells to communicate, exchange resources, and transfer excess sodium ions. The membranes of the cells closest to the salt glands contain specialized s that pump sodium from the cell into the gland. First, proton pumps (H+-ATPases) use chemical energy from the energy-transporting molecule to drive protons into a compartment and establish a proton concentration gradient. Then an ion exchanger, the sodium-hydrogen antiporter, uses the energy of the proton gradient to move sodium ions and protons in opposite directions, at the same time. The process of protons flowing down their concentration gradient releases energy needed by the sodium-hydrogen antiporter to move sodium ions to a compartment already high in sodium. Parts of the gland that aren’t  in contact with the cell are surrounded by a cuticle that prevents ions from flowing back into the cells. The sodium solution becomes concentrated and builds up pressure in the salt gland, which then secretes the salt as a concentrated solution .

This strategy was contributed by Natalie Chen.

Last Updated December 7, 2017