Unraveling Salt Tolerance Mechanisms in Halophytes: A Comparative Study on Four Mediterranean Limonium Species with Different Geographic Distribution Patterns

Abstract

We have performed an extensive study on the responses to salt stress in four related Limonium halophytes with different geographic distribution patterns, during seed germination and early vegetative growth. The aims of the work were twofold: to establish the basis for the different chorology of these species, and to identify relevant mechanisms of salt tolerance dependent on the control of ion transport and osmolyte accumulation. Seeds were germinated in vitro, in the presence of increasing NaCl concentrations, and subjected to “recovery of germination” tests; germination percentages and velocity were determined to establish the relative tolerance and competitiveness of the four Limonium taxa. Salt treatments were also applied to young plants, by 1-month irrigation with NaCl up to 800 mM; then, growth parameters, levels of monovalent and divalent ions (in roots and leaves), and leaf contents of photosynthetic pigments and common osmolytes were determined in control and stressed plants of the four species. Seed germination is the most salt-sensitive developmental phase in Limonium. The different germination behavior of the investigated species appears to be responsible for their geographical range size: L. narbonense and L. virgatum, widespread throughout the Mediterranean, are the most tolerant and the most competitive at higher soil salinities; the endemic L. santapolense and L. girardianum are the most sensitive and more competitive only at lower salinities. During early vegetative growth, all taxa showed a strong tolerance to salt stress, although slightly higher in L. virgatum and L. santapolense. Salt tolerance is based on the efficient transport of Na+ and Cl− to the leaves and on the accumulation of fructose and proline for osmotic adjustment. Despite some species-specific quantitative differences, the accumulation patterns of the different ions were similar in all species, not explaining differences in tolerance, except for the apparent activation of K+ transport to the leaves at high external salinity, observed only in the most tolerant L. narbonense and L. virgatum. This specific response may be therefore relevant for salt tolerance in Limonium. The ecological implications of these results, which can contribute to a more efficient management of salt marshes conservation/regeneration programs, are also discussed.

The CaChiVI2 Gene of Capsicum annuum L. Confers Resistance Against Heat Stress and Infection of Phytophthora capsici

“…It is also investigated that the CBD having cysteine and the hinge region, which is saturated by proline and glycine. The biosynthesis of proline decreases the injury caused by ROS (Schöffl et al, 1999), while in many plant species proline has been considered one of the most common compatible osmolyte for cellular osmotic adjustment which are conferred by the high salinity, water deficit and other stresses (Szabados and Savoure, 2010;Al Hassan et al, 2017;Kumar et al, 2017). Likewise, in our study, the CaChiVI2-overexpressed Arabidopsis revealed significantly FIGURE 10 | CaChiVI2-overexpression effect on drought stress tolerance of transgenic Arabidopsis.…”

Assessing Effects of Temperature Change on Four Limonium Species from Threatened Mediterranean Salt-Affected Habitats

“…Previous studies on these same four species have demonstrated that they are not especially tolerant to presence of salt in the substrate in the germination phase (Al Hassan et al, 2017). In addition, endemics and species with a restricted distribution are predictably the most sensitive to climate change despite their broadly tolerant response to high temperatures, which we proved under laboratory conditions.…”

Insights on Salt Tolerance of Two Endemic Limonium Species from Spain

“…The concentration of 200 mM NaCl drastically affects or, in combination with high temperatures, is even the salinity limit allowing germination for several Iberian Limonium endemics [46][47][48]. On the contrary, in other species of this genus seeds still maintain their germination ability at higher salt concentrations [49][50][51], as in other halophytes [52][53][54][55]. However, a distinctive trait of halophtyes is the recovery of germination capacity even after long periods of exposure to high salt concentrations, a phenomenon that does not occur in glycophytes [56].…”

“…However, in many dicotyledonous halophytes, especially in those more salt-tolerant, moderate concentrations of NaCl stimulate growth [61]. Stimulation of growth under moderate salinity conditions has also been reported in some Limonium species, such as L. delicatulum [62], L. girardianum or L. virgatum [49]. Of the two species studied here, only L. albuferae experienced an increase of FW in the presence of 200 mM NaCl, whereas plants of L. dufourii subjected to the same treatment suffered a reduction of growth of more than 50%.…”