the authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest .
cell - to - cell communication is fundamental to multicellular life . for this to occur effectively there must be pathways and dynamic networks for communication . 
 these might depend upon electrical or chemical signals or the mass transfer of molecules between adjacent cells . 
 molecular communication occurs either via an extra - cellular pathway or through physical structures , called plasmodesmata , that connect the cytoplasm of neighboring cells . 
 plasmodesmata bridge the rigid physical barrier presented by the cell wall to extend the symplasm from single cells to tissue domains that have functional importance for tissue growth , development , and defense . 
 although recent years have seen advances in our knowledge of the physical nature of pd , the trafficked molecules , and of the wider processes they affect , our knowledge of pd structure and function is still relatively rudimentary . 
 this article will consider the technical / experimental difficulties hindering pd research and suggest priorities in the future research effort that might advance the field at a significantly faster rate .