Adaptive responses of a threatened halophyte Juncus rigidus Desf. to salinity stress through anatomy, ionic composition and antioxidant modulations

The Juncus rigidus is an obligatory halophyte and grows commonly in coastal and inland salt marshes, red swamps and lakes. In the present study, internal structure, water content (WC), ionic composition, reactive oxygen species (ROS) and antioxidants (enzymatic and non-enzymatic) were investigated to elucidate the salinity tolerance mechanisms at different salt concentrations (0, 200 and 400 mM NaCl). Detailed anatomical studies showed that chlorenchyma tissue decreased by salinity as compared to control, while number of stomata and number of girders increased only at moderate salinity after 7 days. Vessels showed higher lignification in 200 mM and 400 mM NaCl treatments as compared to control. Na + and Na + /K + increased by increasing salt concentration, while P 3+ and K + decreased in all the treatments. Ca 2+ and Mg 2+ were found decreased with salinity after 14 days, while both increased after 30 days as compared to control. Malondialdehyde (MDA) and O 2 •− contents decreased at 400 mM NaCl only after 7 and 30 days, while H 2 O 2 increased gradually. In general, guaiacol peroxidase (GPX) and polyphenol oxidase (PPO) activities decreased gradually at salinity but superoxide dismutase (SOD) activity increased. Salinity induced significant decrease in Catalase (CAT) activity only after 14 days. The photosynthetic pigments were observed higher at high salinity compared to control plants. The proline and soluble sugar contents were found more at high salinity.