Photosynthetic responses to salinity in two obligate halophytes: Sesuvium portulacastrum and Tecticornia indica

Seedlings of the obligate halophytes Sesuvium portulacastrum L. and Tecticornia indica (Willd.) subsp. indica were grown with 0, 200, or 400 mM NaCl for 13 weeks to investigate whether salt tolerance was related to maintenance of adequate photosynthetic activity and pigment equipment. Both species showed growth optimum at 200 mM NaCl and better tissue hydration under salinity but different photosynthetic response to salinity. CO2 assimilation rate and stomatal conductance of S. portulacastrum were highest at 200 mM NaCl, while in T. indica they decreased with salinity. Pigment content increased under salinity in both species. The de-epoxidation state in S. portulacastrum suggests the need for energy dissipation at 400 mM NaCl, while its salt-induced decline in T. indica, despite the reduced photochemistry, suggests the involvement of adaptive mechanisms other than the xanthophyll cycle.

► Relationship between photosynthetic activity and salt tolerance in two halophytes.
► Growth optimum at 200 mM NaCl and better hydration under salinity in both species.
► Different effects of salinity on photosynthetic parameters between the two species.
► Increased pigment content in both halophytes under salinity.
► Different response of the xanthophyll cycle to salt stress in the two species.