Chapter 11 - Interplay between sodium and chloride decides the plant’s fate under salt and drought stress conditions

Abstract

In saline conditions, sodium (Na+) and chloride (Cl−) ions are considered a major impediment to the growth and development process. The abundance of these two ions in plants decides the overall fate of the plant under salinity stress. A myriad of evidence is present, where the excessive accumulation of sodium (Na+) and chloride (Cl−) leads to irreversible damages. However, NaCl-mediated amelioration is also reported to withstand extreme drought and salt stress and improve photosynthesis and plant metabolism. The chloride (Cl−) ion-mediated repair of stress-induced DNA damage might provide important benefits under salt stress. The primary impact of salinity and drought stress is via osmotic effect, so the immediate downstream signaling process in response to these stresses was similar; however, it differs substantially during the later period of stress. A plant’s sensitivity toward salt stress relies on the modulation of gene expression belonging to the functional (HKT, SOS, NHX, HAK) and regulatory (NAC, MYB) gene families. Among different types of plants, glycophytes are very sensitive to salt stress and, in general, utilize an ion-exclusion mechanism for maintaining ionic and cellular homeostasis and a low Na+/K+ ratio in active plant parts. The SOS, HKT, HAK, PM-ATPase family transporter genes were reported to contribute to better performance of the glycophytes. On the contrary, in halophytes, both ion exclusion and tissue tolerance strategies play a major role as these plants can use Na+ as an osmoregulator. Here, the NHX family transporters and vacuolar ATPase were reported to play a key role. In addition, it was reported that xerophytic plants could utilize NaCl to improve their tolerance to salt and osmotic stresses. Therefore in this compilation, we summarize the relative contribution of sodium (Na+) and chloride (Cl−) ions for deciding the plant’s fate to salt and drought stress and their possible ameliorative roles in stress adaptation and tolerance.