Evolution of halophytes: multiple origins of salt tolerance in land plants

Abstract

Abstract. The evolution of salt tolerance is interesting for several reasons. First, since salt-tolerant plants (halophytes) employ several different mechanisms to deal with salt, the evolution of salt tolerance represents a fascinating case study in the evolution of a complex trait. Second, the diversity of mechanisms employed by halophytes, based on processes common to all plants, sheds light on the way that a plant's physiology can become adapted to deal with extreme conditions. Third, as the amount of salt-affected land increases around the globe, understanding the origins of the diversity of halophytes should provide a basis for the use of novel species in bioremediation and conservation. In this review we pose the question, how many times has salt tolerance evolved since the emergence of the land plants some 450-470 million years ago? We summarise the physiological mechanisms underlying salt-tolerance and provide an overview of the number and diversity of salt-tolerant terrestrial angiosperms (defined as plants that survive to complete their life cycle in at least 200 mM salt). We consider the evolution of halophytes using information from fossils and phylogenies. Finally, we discuss the potential for halophytes to contribute to agriculture and land management and ask why, when there are naturally occurring halophytes, it is proving to be difficult to breed salt-tolerant crops.

The integration of activity in saline environments: problems and perspectives

“…Briefly, they reported that studies of halophyte growth at high concentrations of salts 'offer a rather bewildering array of data'. As halophytes occur in at least 37 orders of plants, (see also Flowers et al 2010), this should not be unexpected. Optimal growth salinities range from 20 to 500 mM with large differences even within single genera (e.g.…”

Salt tolerance of halophytes, research questions reviewed in the perspective of saline agriculture

“…With the evolution of land plants (Graham, 1993), the salt tolerance of their ancestral marine algae, consisting of a salt requirement for amongst other membrane stability and enzyme functioning, has been lost. There are some salt tolerant mosses (Flowers et al, 2010), ferns show no salt tolerance, so most likely salt tolerance secondarily evolved in angiosperms (Fig. 2, Rozema, 1991Rozema, , 1996Flowers et al, 2008Flowers et al, , 2010.…”

Biomass production and Symbiotic Nitrogen Fixation in the Legume Sulla carnosa in its Natural Biotope (sebkha ElKelbia)

“…Attempts to improve the salinity tolerance of conventional crops have not been successful so far. This is because tolerance to salinity is a complex trait [4], involving multiple genes and having evolved multiple times independently among different lineages [7], leading to different mechanisms of salinity tolerance. A different promising strategy is to focus on the de novo domestication of halophytes.…”