Global warming induces several environmental constraints that affect plant growth and production. One of the most significant of these threats is undoubtedly the salinization of the soils that kills most of the crops. In the context of climate change, studying the salt resistance mechanisms developed by some plants, such as the sea rocket, raises the hope to develop new processes and techniques to cure soils of salt.
Sea rocket, a salt-resistant plant
Halophytes are salt-resistant plants, in contrast to glycophyte plants that are salt sensitive. They are mainly present on the seashore, salt lakesides, and others salt areas. Cakile maritima, the sea rocket (Figure 1a), is one of them, growing on coastlines around the world. This plant is able to complete its life cycle with salt up to 500mM NaCl (sea water concentration), and its growth is not impaired up to 100mM NaCl (Figure 1b). In order to understand the cellular mechanisms responsible for its resistance to salt stress, we established a cell culture that provided us with a simplified model to study the salt resistance capacity of the plant (Figure 1c, d).
Figure 1: a, Cakile maritima on a beach in France. b, C. maritima grown in a greenhouse with different concentrations of salt after 20 days of treatment. c, Cell culture of C. maritima. d, C. maritima cells under a microscope. Credit: François Bouteau
We first checked that C. maritima cell cultures present a salt-resistance equivalent to that of the whole plant. This simplified model allowed us to see that the salt managing at the cell level is possible thanks to the regulation of ion transport systems.
Not only these cells limit salt entrance and reduce rapidly the salt concentration inside the cytoplasm, but also they reduce the oxidative stress induced by salt. In addition, C. maritima developed several other resistance mechanisms such as changing their metabolism to cope with the salt-induced osmotic stress and accumulating antioxidants. These cell mechanisms result in different strategies at the whole plant level (Figure 2a); salt could be either excreted from the root; accumulated in aerial parts where it triggers water accumulation leading to leaves succulence (Figure 2b), or excreted on leaves.
Figure 2: a, Halophyte strategies to manage salt at the whole plant level. b, C. maritima succulent leaf accumulating salt and water. Credit: François Bouteau
Halophytes as a new resource
Although quite bitter, Cakile maritima plant is edible, but the consumption of halophytes has disappeared with the end of the great famines in most part of the world. However, in addition to soil desalinization, halophytes are good candidates for different uses on marginal soils, avoiding agriculture soil competition. For example, C. maritima produces oleaginous seeds containing lipid that could be used in the biofuel process and other secondary metabolites that have industrial or pharmaceutical interests. As this plant is resistant to high cadmium concentration in soil, it is also a good candidate for phytoremediation of some marginal soil.
Humanity is starting to realize that living in a finite world implies taking care of natural resources and remedying the polluted environments. The natural capacity of halophytes plants could be a source of benefits for a cohabitation in good intelligence with our environment.
These findings are described in the article entitled Cellular mechanisms to survive salt in the halophyte Cakile maritima, recently published in the journal Plant Science. This work was conducted by Delphine Arbelet-Bonnin, Patrick Laurenti, and François Bouteau from the Université Paris Diderot, Ibtissem Ben Hamed-Laouti from the Université Paris Diderot and the University of Carthage-Tunis, and Chedly Abdelly and Karim Ben Hamed from the University of Carthage-Tunis.