Effects of Exogenous Potassium (K) Application on the Antioxidant Enzymes Activities in Leaves of under NaCl Stress.

Saline soil is a worldwide distributed resource that seriously harms plants' growth and development. NaCl is the most widely distributed salt in saline soil. As a typical representative of halophytes, Lcdcb () is commonly grown in salinized soil, and halophytes have different abilities to retain more K under salt stress conditions. Halophytes can adapt to different salt environments by improving the scavenging activity of reactive oxygen species (ROS) by absorbing and transporting potassium (K). In this study, electron microscope observation, hydrogen peroxide (HO) and malondialdehyde (MDA) contents determination, primary antioxidant enzyme activity determination and transcriptome sequencing analysis were carried out on the leaves of under NaCl stress at 0 h, 48 h and 168 h. The results showed that HO and MDA contents increased in the 200 mM NaCl + 10 mM KCl and 200 mM NaCl groups, but the content increased the most in the 200 mM NaCl group at 168 h. In addition, the leaves of in the 200 mM NaCl + 10 mM KCl group had the most salt secretion, and its superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were all higher than those of the 200 mM NaCl group and significantly higher than those of the control group. According to the results of transcriptome sequencing, it was found that the expression of 39 genes related to antioxidant enzyme activity changed significantly at the transcriptional level. Among them, 15 genes related to antioxidant enzyme activities were upregulated, and 24 genes related to antioxidant enzyme activities were downregulated in the leaves of when exogenous potassium (K) was applied under NaCl stress for 48 h; when exogenous potassium (K) was used for 168 h under NaCl stress, 21 antioxidant enzyme activity-related genes were upregulated, and 18 antioxidant enzyme activity-related genes were downregulated in leaves. Based on the changes of expression levels at different treatment times, 10 key candidates differentially expressed genes (DEGs) (, , , , , , , , and ) for antioxidant enzyme activities were further screened. They played an important role in applying exogenous potassium (K) for 48 h and 168 h to the leaves of in response to NaCl stress. Their expression levels were dominated by upregulation, which enhanced the activity of antioxidant enzymes, and helped mitigate NaCl poison and resist NaCl stress. Particularly, in glutathione S-transferase (GST) activity had the largest log fold-change in the comparison groups of 200 mM NaCl-48 h vs. 200 mM NaCl + 10 mM KCl-48 h and 200 mM NaCl-168 h vs. 200 mM NaCl + 10 mM KCl-168 h. Its expression level was upregulated and played an important role in NaCl toxicity. At the same time, the results of the phylogenetic tree analysis showed that had the closest genetic distance to in the evolutionary relationship. In summary, with the increase of exogenous potassium (K) application time under NaCl stress, can resist high NaCl stress by enhancing antioxidant enzymes' activity and maintaining the growth of Still, it is not enough to completely eliminate NaCl poison. This study provides a theoretical basis for the molecular mechanism of salt tolerance and K mitigation of NaCl poison by the representative halophyte in response to NaCl stress.