  The Stochastic Calculus of Looping Sequences (SCLS) is a recently proposed
modelling language for the representation and simulation of biological systems
behaviour. It has been designed with the aim of combining the simplicity of
notation of rewrite systems with the advantage of compositionality. It also
allows a rather simple and accurate description of biological membranes and
their interactions with the environment.
  In this work we apply SCLS to model a newly discovered ammonium transporter.
This transporter is believed to play a fundamental role for plant mineral
acquisition, which takes place in the arbuscular mycorrhiza, the most
wide-spread plant-fungus symbiosis on earth. Due to its potential application
in agriculture this kind of symbiosis is one of the main focuses of the BioBITs
project.
  In our experiments the passage of NH3 / NH4+ from the fungus to the plant has
been dissected in known and hypothetical mechanisms; with the model so far we
have been able to simulate the behaviour of the system under different
conditions. Our simulations confirmed some of the latest experimental results
about the LjAMT2;2 transporter. The initial simulation results of the modelling
of the symbiosis process are promising and indicate new directions for
biological investigations.
