The effects of glycine betaine and L-arginine on biochemical properties of pot marigold (calendula officinalis L.) under water stress

Pot marigold (Calendula officinalis L.) is widely used due to its various biological activities to treat diseases as an analgesic, anti-diabetic, anti-ulcer and anti-inflammatory agent. To ameliorate the adverse effects of water stress on this medicinal plant, foliar application of glycine betaine (GB) and L-arginine (LA) was used. For this purpose, water stress was applied at three levels (100%, 70% , and 40% field capacity (FC)), and foliar application was used at five levels (control, 50 mM GB, 100 mM GB, 1.5 mM LA, and 3 mM LA) as factorial based on completely randomized  design. We measured phenol and flavonoid content, DPPH radical scavenging activity, superoxide dismutase (SOD) and phenylalanine ammonia-lyase (PAL) activity, and essential oil (EO) content and yield. Total phenol content in the interaction of 40% FC and GB 100 mM was higher than the other treatments. The highest and lowest total flavonoid content and DPPH radical scavenging activity were observed in the interaction of 40% FC and 100% FC, respectively. These variables at GB 100 mM were greater than the others. The highest SOD and PAL activity was found in the interaction of 40% FC and LA 3 mM/GB 100 mM. The content and yield of EO in the interaction of 70% FC and 100 mM GB were greater than other treatments. In sum, 70% of water stress did not significantly change the biochemical properties of C. officinalis, but 40% FC dramatically influenced the quality of the plant. GB 100 mM could stimulate the plant to activate its antioxidant systems under water stress and obtain the highest EO.