Exogenously applied growth regulators affect the growth, phenols, protein and essential oil composition Melissa officinalis

Different growth regulators have been applied to several medicinal plant species to help increasing secondary metabolites’ production in them. The aim of the current study is to analyze the effect of growth regulators’ application, at different concentrations, on Melissa officinalis dry weight production, total phenol and soluble protein contents, and essential oil content and chemical composition. The study has followed a completely randomized design, at 3x3+1 factorial arrangement, which comprised three growth regulators [naphthalene acetic acid (NAA), benzylaminopurine (BAP) and gibberellic acid (GA3)] at three different concentrations (25, 50 and 100 mg L-1), as well as the additional treatment (control), with 4 replications. Growth regulators applied at different concentrations have significantly influenced Melissa officinalis growth. GA3 and NAA regulators’ application at 100 mg L-1 has favored the shoot length and total leaf area of ​​the investigated species. BAP application on leaves, at the highest concentration, led to apical dominance loss; however, the lowest concentration of it has favored soluble protein concentrations in the leaves. BAP application at 25 mg L-1 has favored protein concentrations in the leaves. The highest total phenol contents were observed in plants sprayed with increasing GA3 and BAP doses; they did not differ from the control treatment, only. Essential oil compounds varied depending on the adopted growth regulator type and concentration. GA3 application at the lowest dose (25 mg L-1) resulted in citral content increase by 18% and in citronellal compound content gain ranging from 8% to 10%.