Some salt excluders avoid salt stress by defoliation or abscission (leaf release). When cytosolic salt concentrations approach toxic levels, excess sodium chloride accumulates in petioles, stems that connect leaves to the main stem). The petiole, including the leaf, dies and then detaches from the stem, dropping to the ground. The removal of salt-concentrated parts desalinates the plant, thus preventing buildup of sodium and chloride ions to toxic levels.
Other salt excluders avoid salt toxicity at the roots. The root epidermis (outer layer of cells) of some halophytes may not allow the passage of sodium and chloride ions through the cell membrane. Roots also have an endodermis (inner layer of cells) that contains waxy strips surrounding each cell, to obstruct the entry of sodium and chloride ions. Although this mechanism is less common, selective permeability of the cell membrane (the transport of other ions rather than sodium and chloride ions)
into the roots of halophytes is possible. In some plants, root cells are capable of actively pumping excess sodium and chloride ions out into the surrounding soil.
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