Abstract
Some deleterious effects of drought, soil salinity and other abiotic stresses are mediated by the generation of oxidative stress through an increase in reactive oxygen species (ROS) that damage cellular membranes, proteins and DNA. In response to increased ROS, plants activate an array of enzymatic and non-enzymatic antioxidant defences. We have correlated the activation of these responses with the contrasting tolerance to salinity and drought of three species of the genus Juncus, viz. J. maritimus, J. acutus (both halophytes) and J. articulatus (salt-sensitive). Both stresses were given for 8 weeks to 6-week-old seedlings in a controlled environment chamber. Each stress inhibited growth and degraded photosynthetic pigments in the three species with the most pronounced effects being in J. articulatus. Salt and water stress also generated oxidative stress in all three taxa with J. articulatus being the most affected in terms of accumulation of malondialdehyde (a reliable oxidative stress marker). The apparent lower oxidative stress in halophytic J. maritimus and J. acutus compared with salt-sensitive J. articulatus is explained by a more efficient activation of antioxidant systems since salt or water deficiency induced a stronger accumulation of antioxidant phenolic compounds and flavonoids in J. maritimus and J. acutus than in J. articulatus. Qualitative and quantitative differences in antioxidant enzymes were also detected when comparing the three species and the two stress treatments. Accordingly, glutathione reductase and superoxide dismutase activities increased in the two halophytes under both stresses, but only in response to drought in J. articulatus. In contrast, ascorbate peroxidase activity varied between and within species according to treatment. These results show the relative importance of different antioxidant responses for stress tolerance in species with distinct ecological requirements. The salt-sensitive J. articulatus, contrary to the tolerant taxa, did not activate enzymatic antioxidant responses to salinity-induced oxidative stress.
Highlights
Drought and soil salinity are important environmental stress factors that cause large reductions in global agricultural production and greatly influence the distribution of wild species in nature (Dunson and Travis 1991; Bartels and Sunkar 2005)
In the presence of 100 mM NaCl, FW of the shoots of J. articulatus was 38 % of controls compared with 53 % and 43 % for J. maritimus and J. acutus, respectively
Juncus taxa were quite resistant to salt-induced dehydration in terms of the relative reductions of WC, with water losses of 17 %, 19 % and 25 % for J. maritimus, J. acutus and J. articulatus, respectively, in the presence of 400 mM NaCl (Table 2B)
Summary
Drought and soil salinity are important environmental stress factors that cause large reductions in global agricultural production and greatly influence the distribution of wild species in nature (Dunson and Travis 1991; Bartels and Sunkar 2005). Most plant species cannot tolerate extended drought or saline concentrations over 200 mM NaCl (Hasegawa et al 2000; Flowers and Colmer 2008) because these conditions provoke a series of deleterious effects in the plants that include disturbed cellular osmotic balance, inhibited photosynthesis, inhibition of enzyme activities and cellular processes, and interference with mineral nutrition These effects lead to slower growth and eventually to plant death (Munns and Termaat 1986; Zhu 2001; Munns and Tester 2008). Several ROS, at concentrations much lower than those causing cellular damage, can activate different Naþ- and Kþ-permeable ion channels (Demidchik and Maathuis 2007; Demidchik et al 2007; Richards et al 2014) that help maintain the cytosolic Kþ/Naþ ratios needed for salinity tolerance (Maathuis and Amtmann 1999; Anschutz et al 2014)
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