S04 - Session P1 - New Tools I - NO3- and NH4+ levels of MS medium for the in vitro growth of dragon fruit

Authors: Breno Ítalo Durães Santana, Renato Paiva *, Michele Valquíria dos Reis, Lissa Vasconcellos Vilas Bôas

Dragon fruit ( Hylocereus costaricencise ) is a Cactaceae which is on the rise in the exotic fruit market. Plant tissue culture is a technique that can optimize large-scale seedling production of this culture. The MS culture medium is the most widely used in this technique, however its level of minerals may not be suitable for some species. The aim of this study was to establish adequate levels of nitrate (NO 3 - ) and ammonium (NH 4 + ) in the culture medium for the in vitro growth of dragon fruit seedlings. A single nitrogen source (NH 4 NO 3 ) was used, varying the concentration (1681.61, 2041.955, 2402.3, and 2762.65 mg L -1 ), so that the total nitrogen contents of the MS medium and the concentration of 2402.3 mg L -1 were the same. After 90 days of seed inoculation, the concentration of 2402.3 mg L -1 presented the highest average of fresh mass, seedling height and root length. This concentration allowed an increase of 26% fresh mass when compared to basic MS medium. The different levels of NO 3 - and NH 4 + in the MS medium (39.4 and 20.61 mmol, respectively) and the medium with 2402.3 mg L -1 NH 4 NO 3 (30.01 mmol of both) could exert some influence on seedling growth. In fact, the enzymatic activity of nitrate reductase was low and did not differ between these two treatments, whereas glutamate dehydrogenase was low in the basic MS medium and high in the dose of 2402.3 mg L -1 . Furthermore, the enzymatic activities of glutamine synthase and glutamate synthase were elevated at the highest doses of NH 4 NO 3 . These data show that the preferential route of nitrogen assimilation in this crop is through NH 4 + and its elevated levels might explain the increase in seedling fresh matter. Support: CNPq and Fapemig.