Portulaca oleracea under Salt Stress

Portulaca oleracea (purslane) is an annual succulent halophyte with a great ability to thrive in arid and saline soils that is of pharmaceutical and nutritional value. Several environmental factors such as salinity can affect the final content of bioactive compounds. In this chapter, the plant responses to elevated salt concentrations are evaluated. Studies have demonstrated that plant growth can be induced with moderate salinity (up to 100 mM NaCl), while a marked reduction occurs above this level. Moreover, prolonged exposure to salt stress comes with a considerable variation in several morpho-physiological traits for this plant. Salinity stress induces a rapid increase in substomatal CO₂ concentration and negative CO₂ assimilation values in purslane plants, indicative of the unique ability to shift from the C4 CO₂ fixation mechanism to the crassulacean acid metabolism (CAM). The osmoprotection of purslane plants seems to have an effective reliance on moderate Na⁺ uptake; elevated proline concentrations; besides other compatible solutes that might be involved. The increase in Na⁺/Ca²⁺, Na⁺/K⁺ and Mg²⁺/Ca²⁺ ratios and the discrimination between these ions are key factors for the salt tolerance among purslane accessions. Glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT) enzymes are suggested to be involved in H₂O₂ scavenging in purslane leaves, while non-enzymatic antioxidant molecules are probably involved in the scavenging of superoxide radicals. Salt stress promotes the downregulation of transcription levels of genes involved in photosynthesis, energy metabolism, lignin biosynthesis and signaling transduction. The combination of water salinity with light-emitting diode (LED) lighting (RB, red and blue; and RB+FR, far red lights); salicylic acid (SA); ascorbic acid (Asc); NH₄ ⁺; and/or silicon indicates positive effects on plants’ performances under salt stress. More work is still required for better management of the purslane content of bioactive compounds under saline conditions, and to recommend the proper cultivation practices.