Abstract
Dragonhead (Dracocephalum moldavica L.) has valuable secondary metabolites including rosmarinic acid, anthocyanin, carotenoid and flavonoid which may vary in composition and amount under the effects of environmental factors (e.g. temperature) within a species. Abscisic acid (ABA) has been used to elicit secondary metabolites production. The objective of this study was to evaluate the effect of temperature (at 15, 25 and 35 °C) and exogenous ABA (at the concentrations of 0, 5, 10, 20 and 40 μM) on rosmarinic acid, total phenolic, anthocyanin, carotenoid and flavonoid content of dragonhead. Both growing temperature and ABA application induced a significant change in rosmarinic acid, total phenol and total flavonoid content. Without ABA application, the highest carotenoid, anthocyanin, and flavonoid content were observed in plants grown under the temperature of 15, 35, and 15 °C, respectively, while rosmarinic acid and total phenolic content were not affected by temperature. Treatment of plants with 20 μM of ABA showed 53.56%, 48.87%, and 36.59% increase in rosmarinic acid, total phenolic, and total flavonoid content, respectively, as compared to the control. The increase in rosmarinic acid content was completely correlated with phenylalanine ammonia-lyase (PAL) activity so that PAL activity was enhanced by increasing ABA concentration. Both low (15 °C) and high (35 °C) temperatures significantly decreased leaf area and total dry weight. The results showed that application of 20 μM ABA is the most effective treatment to elicit rosmarinic acid, and phenolics content. We conclude that ABA (especially at the concentration of 20 μM) may induce the accumulation of secondary metabolites including rosmarinic acid, total phenolic, anthocyanin, carotenoid and flavonoid in dragonhead leaves when growth temperature is decreased to 15 °C.
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