Why does in vitro cell selection not improve the salt tolerance of plants?

Abstract

For over a decade cell culture has been advocated in selection programmes for salt tolerance. Selecting cultured cells for survival at high NaC1 potentially offers a fast means for generating, evaluating and selecting genotypes with superior salt tolerance. Furthermore, little space is required and the environment can be controlled. However, plants regenerated from selected cells have not shown unequivocal increases in salt tolerance. Clearly the role of cell culture needs to be reconsidered. This logically begins with an examination of their mechanisms of salt tolerance and how these mechanisms relate to salt tolerance in whole plants. Unfortunately little is known about the mechanisms of salt tolerance in cultured cells, largely due to poor methodology and reluctance to search for mechanisms and test hypotheses. Nonetheless there are ample grounds to propose that tolerance mechanisms in cultured cells are inappropriate or even deleterious to salt tolerance in whole plants. This is partly because salt tolerance is multi-genic and depends on the structural and physiological integrity of the whole plant, and partly because of differences in mechanisms of salt tolerance between cells in culture and cells in whole plants. In vitro selection should therefore be confined to traits where whole plant tolerance is cell based and then only with caution.