Effects of Selenium on Serotonin Synthesis and the Glutathione Redox Cycle in Plum Leaves

Selenium (Se), an essential micronutrient for humans, is also a beneficial nutrient for growth and development of many plants. The aim of the present study was to determine whether low-dose Se application could increase plum growth and serotonin synthesis, as well as upregulate the glutathione redox cycle. Two-year-old plum trees were treated with Se6+(Na2SeO4) and Se2-(SeMet). Growth parameters, levels of serotonin synthesis precursors, compounds and enzymes of the glutathione (GSH) redox cycle, and the antioxidant capacity were analyzed. Results showed that plant height and stem diameter were increased by Se treatment. The leaf Se content was significantly increased; tryptophan was not affected by Se treatment, while the 5-hydroxytryptophan content was significantly higher than control. Although serotonin levels were also increased, the effect was not significant, and no tryptamine was detected in our study. On the 30th day, the MDA content in Se(2-)was highest followed by the control and Se(6+)treatment, and the activities of T-AOT and CAT were increased, while GST was reduced by Se treatment. The two forms of Se treatments increased the activity of GPX and GR, and the total content of GSH + glutathione disulfide (GSSG) at the end of treatment. Furthermore, the level of GSH and GSH/GSSG was instable changed. GSSG content was similar during the treatment time except on the 20 days. Conclusively, the pathway of plum serotonin was clear, both Se(6+)and Se(2-)could influence the serotonin synthesis. Additionally, the GSH redox cycle was sensitive to the Se application. Moreover, Se(6+)performed better than Se(2-)on leaf Se content, plant growth parameters, and antioxidant capacity.