Effect of activated charcoal and 6-benzyladenine on in vitro nitrogen uptake by Lagerstroemia indica

A sterile hydroponic culture system suitable for studying nitrogen (N) uptake of Lagerstroemia indica L. in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with and without 50 muM of 6-benzyladenine (+BA and -BA, respectively). Medium pH, electrical conductivity (EC), NO3- and NH4+ concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO3- and NH4+, although NH4+ uptake was lower. Subsequently the pH of the media was maintained between 5.5-6.0. In treatments with no addition of activated charcoal, NH4+ uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up NO3-, especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition, which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory effect of 50 muM BA on root growth.