In vitro cultivation is the main propagation method for the family Orchidaceae, whereas nitrogen is the most important nutrient in the culture media. This work was carried out to study the influence of different nitrogen concentrations on the in vitro growth of the orchid Phalaenopsis amabilis. Nitrogen concentrations varied by altering the ionic balance of the Murashige & Skoog (MS) culture medium. Plants, 360 days old, were cultivated in liquid MS, modified with 7.5, 15, 30, 45, and 60 mM N. After 180 days, we assessed plant and root length, number of leaves and roots, and fresh and dry weight of leaves, roots and plants. Treatments were assigned to completely randomized plots, with four replications. Plots consisted of five three-plant flasks. The lowest nitrogen level (7.5 mM) in the medium induced root development in length, number, and fresh and dry weight. The concentration 30 mM N stimulated both emission and dry weight accumulation of leaves. The original nitrogen concentration in the MS medium (60 mM) was excessive for the in vitro growth of P. amabilis.

The effects of auxin and the endogenous levels of reserve compounds of Phalaenopsis amabilis (L.) Blume (Orchidaceae) were analyzed in vitro. Rootless plants were inoculated in modified MS media supplemented with IBA or NAA (0.0, 0.2, 1.0 and 5.0 mg L -1 ) and with 2,4-D (0.000, 0.032, 0.160 and 0.800 mg L -1 ). The biochemical parameters of endogenous levels of soluble carbohydrates and starch and of total soluble protein in roots, leaves and shoots were analyzed after 30 and 120 days. Carbohydrate levels in leaves showed similar patterns for all treatments. At 30 days, there was an increase in the endogenous carbohydrate level along with an increase in the concentration of auxins. At 120 days, the endogenous carbohydrate level in leaves had decreased, while the auxin concentration had continued to increase, demonstrating the mobilization of the carbohydrates. The leaf carbohydrate levels decreased from day 30 to 120; for both IBA and 2,4-D treatments, there was starch accumulation in roots as a function of the collection date. The 2,4-D concentration of 0.0032 mg L -1 decreased the level of total soluble protein in roots. The in vitro plants exhibit different growth patterns depending on the classes and concentrations of growth regulators. Biochemical analyses exhibited that metabolic activity and the degradation and accumulation of substances occurs in leaves, roots and shoots, demonstrating that roots contribute to the maintenance of plant metabolism and also act as reserve organs, even in epiphytic plants.