Polyphenols Content in Salinized Seedlings of the Halophytic Legume Prosopis Strombulifera.

REGINATO , MARIANA ANDREA; LUNA, MARÍA VIRGINIA; BECATTI, ELISA; CASTAGNA, ANTONELLA; RANIERI, ANNAMARIA

Nápoles, Italia

Congreso; First Scientific Meeting COST Action FA0901Putting Halophytes to Work-From Genes to Ecosystems; 2010

University of Naples Federico II Italy

Nowadays salinity, which has been representing a threat to agriculture in some parts of the world for more than 3.000 years, is affecting more and more lands. For this reason, to improve knowledge about the specialized physiology and biochemistry of halophyte plants, which are known to own an exceptional degree of salt tolerance, represents a goal for the scientists. Salt stress conditions lead to increased production of reactive oxygen species (ROS) in plant cells. To counteract oxidative stress induced by both biotic and abiotic environmental pressure, such as salinity, plants have developed different strategies, among which the stimulation of the synthesis of secondary metabolites. Among these compounds, phenols play an important role in the defense against reactive ROS. The spiny shrub Prosopis strombulifera (Lam.) Benth., especially abundant in the saline areas of central Argentina, characterized by similar proportions of NaCl and Na2SO4 salts, has been shown to be able to undergo growth stimulation in hydroponic cultures containing 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 growth inhibition. In the present work this species was chosen as a plant model with the aim to determine the effects of increasing concentrations of Na2SO4, NaCl and their iso-osmotic mixture on endogenous polyphenol synthesis. Seedlings of P. strombulifera were allowed to grow hydroponically in Hoagland?s solution, gradually adding Na2SO4 and NaCl separately or in the mixture until reaching a final specific iso-osmotic potentials of -1, -1.9 and -2.6 MPa, whereas control plants were allowed to develop in Hoagland?s solution without salt. Leaves number and root and shoot length were measured weekly and, moreover, the leaf content of total phenols, total flavonoids, total flavan-3-ols, condensed tannins (or proanthocyanidins), tartaric acid esters and flavonols was spectrophotometrically assayed. The results obtained showed that Prosopis strombulifera exhibited a halophytic response to NaCl and, on the contrary, a strong growth inhibition under iso-osmotic solutions of Na2SO4. Treatment with NaCl did not affect polyphenol content, differently from Na2SO4 which sharply induced an increase in flavonoid compounds, mainly total flavan-3-ols. In conclusion, ionic interactions between different kinds of salt, frequently found in soils, are supposed to modify the physiological responses to salinity. In Prosopis strombulifera the increase in total flavan-3-ols, when SO42- anion is present in the growth solution, may indicate a role for these compounds in counteracting the damage induced by severe salt stress.