Tolerance to high soil [Na(+)] involves processes in many different parts of the plant,
and is manifested in a wide range of specializations at disparate levels of organization,
such as gross morphology, membrane transport, biochemistry and gene transcription.
Multiple adaptations to high [Na(+)] operate concurrently within a particular plant,
and mechanisms of tolerance show large taxonomic variation. These mechanisms can occur
in all cells within the plant, or can occur in specific cell types, reflecting adaptations
at two major levels of organization: those that confer tolerance to individual cells,
and those that contribute to tolerance not of cells per se, but of the whole plant.
Salt-tolerant cells can contribute to salt tolerance of plants; but we suggest that
equally important in a wide range of conditions are processes involving the management
of Na(+) movements within the plant. These require specific cell types in specific
locations within the plant catalysing transport in a coordinated manner. For further
understanding of whole plant tolerance, we require more knowledge of cell-specific
transport processes and the consequences of manipulation of transporters and signalling
elements in specific cell types.