Saline soils and salt water have become more and more dominant through the centuries, and naturally occurring salt-affected soils are estimated to cover a billion hectares worldwide. Scientists are thus trying to duplicate – but to little success – what Nature has done for some trees, shrubs, grasses, and herbs: allow plants to be salt-tolerant. In light of this problem, T.J. Flowers and S.A. Flowers of the University of Sussex ask, “Why does salinity pose such a difficult problem for plant breeders?” Their review appears in the September issue of the Agricultural Water Management journal

Salt-tolerance, as it turns out, is a very complex genetic trait. In the article, researchers recount most of the molecular mechanisms underlying plant defenses against salty soils or water. This is accomplished by the presence of organic compounds in plant cell cytoplasm, such as glycinebetaine, mannitol and proline. Salt tolerance also depends on plant morphology, compartmentation and compatible solutes, regulation of plant transpiration, control of ion movement, plant cell membrane characteristics, tolerating high Na/K ratios in the cytoplasm, and salt glands. With these many factors, the authors expect that salt tolerance would depend on the action of many genes.

With the rather daunting tasks ahead for bioengineers seeking to produce salt tolerant plants, researchers recommend that plant breeders “invest in other avenues such as the manipulation of ion excretion from leaves through salt glands, the use of physiological traits in breeding programs, and the domestication of halophytes.”

Subscribers to ScienceDirect can read the complete article at http://dx.doi.org/10.1016/j.agwat.2005.04.015.