Intercellular Trafficking of Macromolecules During Embryogenesis

Plasmodesmata provide routes for communication and nutrient transfer between plant cells by interconnecting the cytoplasm of adjacent cells. A simple fluorescent tracer-loading assay was developed to monitor patterns of cell to cell transport via plasmodesmata specifically during embryogenesis. A developmental transition in plasmodesmatal size exclusion limit was found to occur at the torpedo stage of embryogenesis in Arabidopsis ; at this time, plasmodesmata are downregulated, allowing transport of small (∼0.5 kDa) but not large (∼10 kDa) tracers. This assay system was used to screen for embryo defective mutants, designated increased size exclusion limit of plasmodesmata that maintain dilated plasmodesmata at the torpedo stage.