Responses of Batis maritima plants challenged with up to two-fold seawater NaCl salinity

Batis maritima is a promising halophyte for sand-dune stabilization and saline-soil reclamation. This species has also applications in herbal medicine and as an oilseed crop. Here, we address the plant response to salinity reaching up to two-fold seawater concentration (0–1000 mM NaCl), with a particular emphasis on growth, water status, mineral nutrition, proline content, and photosystem II integrity. Plant biomass production was maximal at 200 mM NaCl, and the plants survived even when challenged with 1000 mM NaCl. Plant water status was not impaired by the high accumulation of sodium in shoots, suggesting that Na+ compartmentalization efficiently took place in vacuoles. Concentrations of Mg2+ and K+ in shoots were markedly lower in salt-treated plants, while that of Ca2+ was less affected. Soluble-sugar and chlorophyll concentrations were hardly affected by salinity, whereas proline concentration increased significantly in shoots of salt-treated plants. Maximum quantum efficiency (Fv/Fm), quantum yield of PSII (ΦPSII), and electron-transport rate (ETR) were maximal at 200–300 mM NaCl. Both nonphotochemical quenching (NPQ) and photochemical quenching (qP) were salt-independent. Interestingly, transferring the plants previously challenged with supraoptimal salinities (400–1000 mM NaCl) to the optimal salinity (200 mM NaCl) substantially restored their growth activity. Altogether, our results indicate that B. maritima is an obligate halophyte, requiring high salt concentrations for optimal growth, and surviving long-term extreme salinity. Such a performance could be ascribed to the plant capability to use sodium for osmotic adjustment, selective absorption of K+ over Na+ in concomitance with the stability of PSII functioning, and the absence of photosynthetic pigment degradation.