Multiple mechanisms mediate growth and survival in young seedlings of two populations of the halophyte Atriplex halimus (L) subjected to long single step salinity treatments
Understanding how halophytes survive high soil salinity in realistic long-term experiments is important for strategies to mitigate the effects of increasing soil salinity worldwide. Protective mechanisms in halophytes enabling survival include sequestration of salt via Na+/H+ antiporters, synthesis and accumulation of osmolytes, and activation of protective mechanisms against reactive oxygen species (ROS). Protective mechanisms elicited by a single step-up to a range of NaCl treatments (34–256 mM) in two populations of the halophyte Atriplex halimus L. from contrasting environments (arid steppe and saline coastline) were compared over 6 weeks. The coastal population survived significantly better at high salinity compared with the steppe population, although in both populations, salinity inhibited growth. Increased Na+ and K+ concentration was accompanied by higher induction of Na+/H+ antiporter gene expression in coastal than in steppe population leaves. Osmolytes increased more significantly in the coastal than in the steppe population with greater induction of choline mono-oxygenase gene expression. Activation of ROS scavenging mechanisms was greater in coastal than in steppe plants. Differential responses found through time, in different salt concentrations, and between leaves and roots indicate a finely tuned response. Sharp changes in responses at 171 mM NaCl indicate that different mechanisms may be invoked at different stress levels.</jats:p
