Licorice (Glycyrrhiza glabra L.) is a valuable plant for the treatment of several diseases. Negative effects of aluminum stress on plants have been reported and silicon may alleviate these negative effects through promoting antioxidant system. This study was conducted to investigate the effects of silicon on glycine-betaine, phytochelatin, and antioxidant parameters in licorice plant under aluminum stress. The plants were treated with silicon (0, 0.5, and 1.50 mM) and submitted to aluminum stress (100, 250, and 400 µM). Glycine-betaine contents of roots and shoots were investigated. Also, guaiacol peroxidase (GPx), peroxidase (POX), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities, and hydrogen peroxide (H2O2) and root phytochelatin were assessed after treatment with aluminum. Results showed that aluminum stress increased the contents of glycine-betaine and root phytochelatin, activities of GPx, POX, SOD, PAL, DPPH radical scavenging, and H2O2 content (p <0.05). Application of silicon application also increased the contents of glycine-betaine, activities of GPx, POX, PAL, DPPH radical scavenging, and root phytochelatin (p <0.05) while it decreased H2O2 and SOD contents (p <0.05). Based on the findings, application of silicon is recommended for protection of licorice under aluminum stress. Manuscript profile

Basil (Ocimum basilicum L.) is one of the valuable medicinal plants. Negative effects of NaCl stress on plants have been reported and silicon may alleviate these negative effects through promoting antioxidant system. This study was conducted to investigate the effects of silicon as elicitor and NaCl as salinity stress on some morphological, biochemical, and antioxidant parameters in basil plant. The plants were pretreated with silicon (0, 0.5, and 1.50 mM) and submitted to NaCl stress (0, 50 and 100 mM). Results showed that NaCl stress decreased dry and fresh weight of shoot and root, cholorophyll and carbohydrate content, but carotenoid, hydrogen peroxide (H2O2) content, superoxide dismutase (SOD) and catalase (CAT) activity increased (p<0.05). Silicon also increased dry and fresh weight of shoot and root, carotenoid, chlorophyll and carbohydrate content, CAT and SOD activity but H2O2 content decreased (p<0.05). Based on these results, silicon especially 1.50 mM concentration is recommended for protection of basil under NaCl stress. Manuscript profile