The plant hormone auxin regulates many aspects of plant growth and development. It is known that auxin movement within plant tissues depends on the spatial distribution of auxin efflux and influx carriers. Now, Leah Band and colleagues investigate how flow through plasmodesmata – small pores that link the cytoplasm of plant cells – can also contribute to auxin distribution. They first develop a multicellular mathematical model to simulate auxin distribution under various genetic and chemical perturbations. By comparing the auxin distribution patterns predicted by this model to those observed experimentally (using a DII-VENUS auxin response reporter), they reveal that root-tip auxin distribution cannot be accounted for by carrier-mediated transport alone. Following on from this, they incorporate flux through plasmodesmata into their model and report that this improves the agreement between the modelling and experimental data. The researchers further show that modifying the density and permeability of plasmodesmata within the model significantly affects auxin distribution. Accordingly, they demonstrate that the experimental manipulation of plasmodesmata permeability, either chemically (using H2O2) or genetically (by lowering the levels of GLUCAN SYNTHASE LIKE 8, which regulates plasmodesmata callose deposition) perturbs auxin distribution. Together, these findings suggest that auxin diffusion through plasmodesmata has a major impact on root-tip auxin distribution.
