Physiological adaptation and gene expression analysis of Casuarina equisetifolia under salt stress

Abstract

Casuarina equisetifolia is widely planted in coastal areas of tropical and subtropical regions as windbreaks or to stabilize dunes against wind erosion due to its high salt tolerance and nitrogen-fixing ability. To investigate the mechanisms responsible for its salt tolerance, we examined growth, mineral composition, expression of genes for sodium (Na +) and potassium (K +) transport proteins, and antioxidant responses under NaCl treatments. Increasing NaCl concentrations inhibited lateral root elongation and decreased plant height, length of internodes, and numbers of branches and twigs. The Na + content significantly increased whereas the K + content significantly decreased in both shoots and roots with increasing external NaCl concentration, resulting in a significant increase in Na + /K + ratio. Most of the Na + /H + antiporter genes (NHXs) were obviously upregulated in roots after 24 and 168 h of salt stress, and NHX7 was especially induced after 168 h. Almost all salt overly sensitive (SOS) genes were induced after 168-h treatment. Additionally, activities of superoxide dismutase, glutathione peroxidase, and catalase were significantly changed in shoots and roots under salt stress. Hence, we conclude that salinity tolerance of C. equisetifolia mainly relied on sequestering excess Na + into vacuoles and on induced expression of NHX and SOS genes in roots and thus the maintenance of sufficient K + content in shoots.

Transcriptome and structure analysis in root of Casuarina equisetifolia under NaCl treatment

“…Their roots were washed and the plants were transferred to containers filled with clean water and allowed to grow for 2 weeks until new roots appeared. Plants were then transferred to Hoagland solution containing 200 mM NaCl based on a previous study ( Fan et al, 2018 ) and allowed to grow for varying durations. The solution was replaced with fresh solution every day.…”

“…Similarly, C. glauca tolerates high levels of salinity by changing the levels of some neutral sugars, proline, and ornithine ( Jorge et al, 2017 ). In addition, greater amounts of Na + are adsorbed over the roots under salt stress, and expression of NHX and SOS genes in roots helps to maintain K + balance, an essential part of the response to excess salt in C. equisetifolia ( Fan et al, 2018 ). However, the unique strategies adopted by these plants for dealing with salinity and the salt-tolerance mechanisms of these species remain unclear.…”

“…Sodium sensors in roots allow plants to respond quickly to stress, such as the rapid salt-specific response in roots and the rapid, sodium-specific effect of salt on root growth direction (salt solubility) ( Choi et al, 2014 ; Galvan-Ampudia et al, 2013 ). Roots of C. equisetifolia are tolerant of salt stress in saline soil ( Tani & Sasakawa, 2003 ; Fan et al, 2018 ). However, there are few studies on the response mechanism in C. equisetifolia roots under salt stress.…”

Mechanisms of salt stress tolerance in Casuarina: a review of recent research

“…For example, in C. obesa, the tolerance to high salinity levels was related to the exclusion of ions (Carter et al 2006a;Isla et al 2014), osmotic adjustments, accumulation of compatible organic solutes, and photoprotective mechanisms (Carter et al 2006a,b). Accordingly, ion extrusion (Fan et al 2018;Gupta et al 2018) and osmolyte accumulation (Tani and Sasakawa 2006) were also implicated as important salt tolerance mechanisms in C. equisetifolia. In this species, ion translocation to shoots and retention in roots were observed, suggesting the existence of alternative mechanisms to protect cells from Na + (Selvakesavan et al 2016).…”

Effects of arbuscular mycorrhizal fungus on sodium and chloride ion channels of Casuarina glauca under salt stress

“…Hence, it helps to improve the ecological environment by providing materials (Djighaly et al 2018;Ye et al 2019). As a coastal shelterbelt species, C. glauca is mainly exposed to Na + and Cl − toxicity (Fan et al 2018;Vikashini et al 2018). Djighaly et al (2018) found that C. glauca was more tolerant to NaCl stress than C. equisetifolia, and inoculation with AMF could improve the uptake of nutrients (such as N and P) and water of C. glauca under NaCl stress.…”