Effect of Different Plant Growth Regulators, Explant Types and Light on Callogenesis Traits of Medicinal Plant Nettle (Urtica dioica L.)

Nettle (Urtica dioica L.) is considered a valuable plant with high level of various beneficial phytochemical, which has been used centuries in traditional medicine. Since it contains various secondary metabolites and shows noticeable activity against different Gram-positive and Gram-negative bacteria, nettle has been identified as an appropriate choice for wider applications in the food and pharmaceutical industries in the recent years. This plant is native to Asia, Europe, Africa and North America and grows naturally in different regions of Iran. Although nettle is an important medicinal plant worldwide, there is no information about optimization of its tissue culture conditions. This study was carried out to investigate the effects of different plant growth regulators, explant types and light condition on the callogenesis properties of nettle plant under in vitro condition.

A factorial experiment was carried out on the base of completely randomized design with three replicates. Different explants including young leaves, old leaves, nodes and seeds of nettle plant were cultured in the solid MS medium supplemented with 30 g l-1 sucrose and different concentrations of plant growth regulators of 2,4-D (1, 2 and 3 mg l-1) and BA (0.1, 0.5 and 1 mg l-1). Callus-related characteristics, including time of callus induction, callogenesis percentage, and their color and texture were analyzed. Analysis of variance was carried out by SAS software ver. 9.3.1 and mean comparison was conducted using Duncan multiple range test.

According to the results, callus induction was significantly influenced by explant type. The highest callus induction was attained from young leaves, nodes and old leaves, respectively. The results also showed that callus induction and its properties were significantly influenced by light condition. Preservation of cultures in dark condition resulted in higher callus induction than light condition. In addition, the effect of plant growth regulators was significant on callus induction and its properties. The highest percentage of callus induction was obtained from young leaf explants in the medium containing 1 mg l-1 2,4-D and 1 mg l-1 BA in dark condition followed by node explants in the same plant growth regulator treatment. However, medium supplemented with 1 mg l-1 2,4-D and 0.1 mg l-1 BA showed to be more effective for old leaf explants. Based on the results of this research, young leaf explants in the MS medium containing 1 mg l-1 2,4-D and 1 mg l-1 BA in dark condition are suggested for callus induction from nettle plant.

Type, color and amount of produced callus in different plant species are highly dependent on the genotypes, compositions of tissue culture media as well as the levels of both endogenous and exogenous plant growth regulators. Auxin and cytokinin are two main plant growth regulators playing important roles in callogenesis of different plant species. There is an interaction between the level of plant growth regulators and color of produced callus. Based on the results of present study, it seems that in the nettle plant, node explants endure a higher level of plant growth regulators and hence produce a brighter callus than the leaf segment explants when they are treated with high concentrations of these chemicals.