Salinity influences arsenic resistance in the xerohalophyte Atriplex atacamensis Phil.

Abstract

Arsenic (As) is a highly toxic element accumulating in the environment as a result of anthropogenic activity. In Northern Chile it accumulates in salt areas and constitutes a major threat for human population. Atriplex atacamensis is a perennial halophyte shrub spontaneously growing in these contaminated areas. In order to determine the impact of salinity on As absorption and accumulation in A. atacamensis, young seedlings obtained from seeds collected on an As-polluted area were cultivated for 2 and 4 weeks in nutrient solutions containing no As and no NaCl (control), NaCl 100mM, As(V) 1000μM and NaCl 100mM+As(V) 1000μM. Speciation analysis indicates that arsenic in the solution remained in the As(V) form. Roots accumulated high concentration of As (up to 5020μgg−1 DW): 55% of total extractable As was in the reduced state As(III) and 45% as As(V). More than half of the total As accumulated in cell walls. The leaves accumulated lower amounts of total As, with a majority of As(V) in the extractable fraction. Addition of NaCl to the As-containing nutrient solution reduced As concentration in the roots and increased the proportion of As(V) comparatively to As(III). Salinity strongly increased As translocation from the root to the shoot but did not modify its distribution between apoplasm and symplasm compartments. Exogenous salinity reduced the As-induced senescing ethylene synthesis in As-treated plants and contributed to a more efficient antioxydation system. Salinity and As induced the synthesis of major protective molecules (proline, glycinebetaine, trigonelline, polyamines, non-protein thiols), some of them being involved in short-term response to ion toxicities while others appeared to be required for longer period. It is concluded that Atriplex atacamensis is an interesting tool for the phytomanagement of As-contaminated area and that salinity improves the plant resistance to this dangerous pollutant.