Influence of light quality and some growth regulators in inducing the production of Podophyllotoxin, a bioactive compound against cancer, in adventitious roots formed in the leaves of Hyptis suaveolens

Abstract

Podophyllotoxin (PTOX) is an aryltetraline lignan used to treat skin lesions, such as warts, human papilloma virus, and genital infections. Hyptis suaveolens has PTOX in its roots and the culture of its plant tissues in vitro has been increasingly used to produce rare and high-quality medicinal compounds. Adventitious roots are an attractive source of phytochemicals due to their genetic and biosynthetic stability. Thus, the aim of the present study is to investigate adventitious roots’ induction in leaves and nodal segments under different light qualities and auxins in H. suaveolens. Adventitious roots have only emerged in H. suaveolens leaves grown in semi-solid MS medium, in the absence of light and under red light-emitting diode (LED). Root dry weight values recorded for these treatments were statistically equal to each other, i.e., 21.84 and 29.81 mg, respectively. PTOX quantification was performed in the dark (10.72 µg g−1) and under red LED (9.93 µg g−1). Indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA) (0.5, 1.0 and 2.0 mg L−1) concentrations induced adventitious roots’ formation in leaves of plants belonging to this species. Explant supplemented with 2.0 mg L−1 NAA led to higher root dry weight (45.53 mg) in leaves. However, the 1.0 mg L−1 IBA treatment produced more PTOX (9.96 µg g−1 root). Nodal segments of H. suaveolens, IBA and NAA concentrations (0.5, 1.0 and 2.0 mg L−1) also induced adventitious roots’ formation. The treatment with 0.5 mg L−1 IBA resulted in higher root dry weight (37.62 mg) in the nodal segment. However, 1 and 2 mg L−1 IBA resulted in lower root dry weight and higher PTOX (9.97 µg g−1 and 9.95 µg g−1). In conclusion, adventitious root formation and PTOX induction in H. suaveolens leaves grown in semi-solid MS medium only happen in plants grown in the dark and under monochromatic red LED light. Growth regulator NAA was the best element to induce adventitious roots’ emergence in leaves, whereas IBA was the best one for such a purpose in nodal segment. Growth regulator NAA can inhibit the synthesis of PTOX, but IBA induces this secondary compound.