Different tolerance to sodium chloride and sulfate of the halophyte Prosopis strombulifera: analysis of polyphenols and photosynthetic leaf pigments

REGINATO , MARIANA ANDREA; LUNA, MARÍA VIRGINIA; CASTAGNA, ANTONELLA; SCATTINO, CLAUDIA; RANIERI, ANNAMARIA

Hannover

Congreso; WG2 Meeting 2012 Putting Halophytes to Work-Genetics, Biochemistry, Physiology; 2012

Salinity is one of the major environmental constraints which affect plant productivity and crop yields worldwide. For that reason, to improve knowledge about the specialized physiology and biochemistry of halophytes represents a goal for the scientists. Salt stress conditions are known to increase the production of reactive oxygen species (ROS) and induce ROS-dependent injury. To counteract oxidative stress plants have developed different strategies, among which the stimulation of the synthesis of secondary metabolites, like polyphenols. The halophyte Prosopis strombulifera (Lam.) Benth., especially abundant in the saline areas of central Argentina (characterized by soils with similar proportions of NaCl and Na2SO4 salts) has been shown to be able to undergo growth stimulation up to 500 mM NaCl and to survive under very high concentrations (as much as 1 M NaCl). Moreover, P. strombulifera has been previously found to be much less tolerant to Na2SO4, presenting a strong and sustained growth inhibition. In this study, P. strombulifera was chosen as a plant model to analyze the effects of increasing concentrations of Na2SO4, NaCl and their iso-osmotic mixture on lipid peroxidation, leaf pigment content and pattern, polyphenol content and antioxidant capacity. Seedlings of P. strombulifera were hydroponically cultured in Hoagland?s solution, gradually adding Na2SO4 and NaCl separately or in the iso-osmotic mixture until reaching final -osmotic potentials of -1, -1.9 and -2.6 MPa. Control plants were allowed to develop in Hoagland?s solution without salt. Lipid peroxidation was determined as malondialdehyde content (MDA). Total phenols, flavonoids, flavan-3-ols, proanthocyanidins, tartaric acid esters and flavonols were spectrophotometrically assayed. Leaf pigment concentrations and patterns were analyzed by HPLC. Additionally, the antioxidant capacity of poliphenols extracts was assayed by the ABTS method. The results obtained showed that treatment with Na2SO4 induced a higher lipid peroxidation in P. strombulifera, with an important increase in MDA accumulation in leaves at -2.6 MPa. NaCl did not affect polyphenol synthesis, differently from Na2SO4 which induced a sharp increase in total phenols and flavonoid compounds (mainly total flavan-3-ols) and, consequently, in the antioxidant activity in both leaves and roots. Similarly, leaf pigment pattern was affected only by Na2SO4, which led to a decrease in chlorophylls content. Carotenoids content remained unaffected by salt treatments. The de-epoxidation index (DEPS index, based on antheraxanthin, zeaxanthin and violaxanthin contents) significantly increased only under Na2SO4 treatment at -2.6 MPa, indicating the need to alleviate excessive excitation pressure under a prolonged exposure to high salt concentration. In conclusion, ionic interactions between different kinds of salts are supposed to modify the physiological responses to salinity. In P. strombulifera, the increase in phenol compounds, antioxidant activity and DEPS index when SO42- anion is present in the growth solution suggests a role for these compounds in counteracting the oxidative damage induced by severe salt stress.