Adventitious Root Development and Secondary Metabolites Accumulation by Auxin in Cichorium intybus L

Adventitious root cultures of medicinal plants are a source of secondary metabolites of pharmaceutical importance, and are considered as an alternative method for clonal propagation and germplasm conservation in medicinal plants.Chicory (Cichorium intybus L.) is a medicinal plant from Asteraceae and isused in traditional medicine to promote appetite and digestion. This plant contains many important metabolites including chicoric asid, inulin, scoline, coumarin and flavonoids. In the current research, an efficient protocol has been developed for adventitious root culture on MS medium supplemented with different concentrations of Indole-3-acetic acid (IAA) and α-Naphthalene acetic acid (NAA).

The seeds were surface-sterilized with 50 ml l−1 sodium hypochlorite for 20 min, subsequently with 700 ml l−1 ethanol for 90 s. The surface-sterilized seeds were inoculated against the MS medium and cultures were incubated at 25 ±2 ◦C under fluorescent light for a cycle of 16 h light and 8 h dark per day. The leaves explants of 28-day-old in vitro plantlets were used as explants. For root initiation, IAA (0, 0.2, 0.4 and 0.6 mg l-1) and NAA (0, 0.5, 1 and 1.5 mg l-1) were used. After four weeks, the well-established roots were separated. To determine the best medium of composition for growth of roots, approximately 100 mg fresh weight of adventitious roots were cultured in MS liquid medium with different concentrations of IAA (0, 0.5, 1 and 1.5 mg 1-1) and NAA (0, 0.5, 1 and 1.5 mg 1-1).

According to the results, among the different concentrations of IAA, the highest root induction (72.5 percent), root number (4.75), and root branch (10.08) were exhibited by 1.5 mg/L IAA. Among different NAA levels, the highest root induction (88.88 percent), and root number (8.04) were observed in 1.5 mg/L NAA and was not significantly different from 0.5 and 1.5 mg/L NAA. This hormone at concentration of 1.5 mg/L, induced the highest root branching (18.42 per explant). The highest fresh weight (0.74 g) and dry weight (0.062 g), growth index (6.51), and phenol (4.1 mg/g DW) were obtained in MS liquid medium containing 0.5 mg 1-1 NAA in combination with 0.5 mg 1-1 IAA, and Flavonoid content in 270, 300 and 330 nm wavelengths was higher (60.26, 85.88 and 98.53 µg g-1 DW) in the roots obtained from 1 mg l−1 of NAA in combination with 1 mg l−1 of IAA. Increasing NAA concentrations induced callus mediated root formation and produced a lower number of adventitious roots. By using IAA, adventitious roots were initiated, but the frequency and average number of roots initiated were lower when compared with NAA.

Adventitious roots obtained by different concentration of auxins are a suitable tool for the production of plant secondary metabolites due to their genetic stability, and generally, show a fast growth rate. This study describes the protocol for adventitious root induction which could further be useful for the production of secondary metabolites and biomass