Salt Stress Tolerance in Casuarina glauca and Its Relation with Nitrogen-Fixing Frankia Bacteria

Comparative Proteomic Analysis of Nodulated and Non-Nodulated Casuarina glauca Sieb. ex Spreng. Grown under Salinity Conditions Using Sequential Window Acquisition of All Theoretical Mass Spectra (SWATH-MS)

“…Moreover, the difference between KNO 3 + and NOD + plants regarding the number of DEPs might be associated with the fact that the process of nodulation in C. glauca leads to a set of defense-related events, such as the transcriptional activation of defense-related genes encoding proteins involved in ROS-detoxification [2,3], or the protection of nodules against pathogenic microorganisms [3,38], probably triggering a systemic defense response. On the other hand, the fact that at 200 mM NaCl Frankia was no longer fixing nitrogen in C. glauca nodules, and thus at this salt concentration the plants were subjected to both salt and mineral stresses [12], may explain the slightly higher induction of DEPs in NOD + than in KNO 3 + at 200 (24% vs. 16%) and 400 mM (56% vs. 44%), which was then similar at 600 mM NaCl (93%) when major physiological changes related to photosynthesis, membrane stability and osmoprotection mechanisms are induced [4,7,8,13,21,22]. At any rate, in both plant groups, the number of DEPs was regulated in a gradual manner, accompanying the severity increase of salt stress imposition, likely reflecting changes towards acclimation to high salt exposure.…”

“…Salt stress in Casuarina glauca induces a complex array of physiological and biochemical responses that collectively lead to stress tolerance [6,13]. These include photosynthetic adjustments related to the functioning of the photosynthetic machinery [4], as well as the activity of antioxidant enzymes closely related to maintenance of cell membrane integrity [21], osmotic balance [7,8], and lipid matrix remodeling [21].…”

“…Among the 357 quantified proteins, 43 were regulated by salt stress in KNO 3 + plants and 25 in NOD + plants, 19 of which were common to both groups (Figure 1a,b). The first important information regards the stability of most of the identified proteins, likely linked to the maintenance of plant performance under salt stress [6,12,13,21]. Additionally, such a low number of differentially expressed proteins (DEPs) might be explained by the assumption that C. glauca has constitutive defense mechanisms against various stresses and that defense responses are activated during the early stages of stress imposition [21].…”

“…C. glauca is a tropical tree widely used to prevent desertification and erosion, as well as to rehabilitate poor and degraded soils [1,10]. Such capacity does not necessarily depend on the symbiosis with Frankia, although some strains may enhance stress tolerance [4][5][6]9,[11][12][13].…”

“…Recently, the mechanisms underlying salt stress tolerance in C. glauca and the contribution of symbiotic nitrogen fixation have been thoroughly analysed by our team. For that, we have examined the impact of increasing NaCl concentrations (200, 400 and 600 mM) on plant growth, mineral contents, water relations, photosynthesis-related parameters and non-structural sugars [4,12,13], membrane integrity and the control of oxidative stress [21], as well as the metabolome of nodules, roots and branchlets from nodulated and non-nodulated C. glauca plants [7,8,22]. According to Batista-Santos et al [4], the C. glauca ecotype used in these studies exhibits outstanding salt stress tolerance showing the first stress symptoms, i.e., phenotypic changes (chlorosis and necrosis of branchlets, reduction of stem diameter and biomass decrease in both KNO 3 + and NOD + groups; and swollen nodules with salt crystals at the surface in NOD + plants), and the impairment of photochemical (e.g., photosynthetic electron flow) and biochemical (e.g., activity of photosynthetic enzymes) parameters only at 600 mM NaCl.…”