Cross-generic studies with rice indicate that ion homeostasis and antioxidant defense is associated with superior salinity tolerance in Cynodon dactylon (L.) Pers.

Abstract

A study was undertaken to evaluate the salt-tolerant attributes of Cynodon dactylon by comparing it with three varieties of the model glycophyte crop rice (Oryza sativa L.). For cross generic studies, all plants were uprooted and transferred to 0.1× Hoagland solution supplemented with 0, 10, 100, 200 and 500 mM NaCl. All plants were exposed to NaCl shock for 24 and 72 h. One of the most important attribute that conferred salinity tolerance in Cynodon was the presence of sodium ion exclusion mechanism in leaves. At high NaCl concentrations (200 and 500 mM NaCl), Na+ exclusion from the leaves was observed after 3 days. This helped to maintain a high K+/Na+ ratio inside the leaf tissues. The activity of different antioxidative enzymes such as superoxide dismutase, ascorbate peroxidase, catalase, peroxidase, and glutathione reductase were also evaluated, and it was observed that the synchronised activity of these enzymes was responsible for the detoxification of reactive oxygen species (ROS) generated under salinity stress in Cynodon. The relatively stable and controlled level of H2O2 and membrane lipid peroxidation in Cynodon with the increase in NaCl concentration and time of treatment could be due to efficient antioxidant machinery. Additionally, the controlled and least affected relative water content in leaves and roots of Cynodon in comparison to the rice varieties can be linked to the enhanced accumulation of proline and sugars, which helped to maintain the osmotic balance. On the other hand, all the three rice varieties lacked Na+ exclusion mechanism and efficient ROS scavenging system at par with Cynodon, as evidenced by higher oxidative stress markers such as lipid peroxidation, and H2O2 and lower activity of antioxidant enzymes. Besides there was little inter-varietal differences among the rice varieties in terms of NaCl tolerance.