The regulation of antioxidant enzymes in two Plantago species differing in salinity tolerance under combination of waterlogging and salinity

Abstract

Natural waterlogging affects vegetation dynamics in many areas of the world. Goose-tongue (Plantago spp.) plants include diverse group of species differing in salt tolerance, some of which are adapted to live in saline wetlands, which makes the genus Plantago a good model for comparative studies on the responses to waterlogging and salinity stresses. The aim of this study was to determine how waterlogging in combination with 200 mM NaCl affect the tolerance mechanism of Plantago maritima L. (salt-tolerant) and Plantago media L. (salt-sensitive). Combination of salinity and waterlogging treatments (WLS) decreased shoot and root dry weights (DW) and leaf relative water content (RWC) of both P. maritima and P. media and these decreases were more dramatic in the latter. Lipid peroxidation level as measured by thiobarbutiric acid reactive substances (TBARS) content was increased in P. maritima by the combined salinity and waterlogging treatment, whereas in P. media it was increased by all stress treatments applied. Peroxidases (POX), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activities of P. maritima were increased whereas only POX and CAT activities of P. media were increased by salinity treatment alone. WLS treatment increased POX, APX and GR activities but did not affect CAT activities of both Plantago species. NADPH oxidase (NOX) activity did not seem to have any effect to control the level of lipid peroxidation. This study is the first to demonstrate that increased antioxidant activity protected against lipid peroxidation resulting from waterlogging and salinity stresses. In conclusion, we suggest that a salt-tolerant species would also have a higher tolerance of the combination of waterlogging and salinity stress than a salt-sensitive one.