On the origin of microcraters on the surface of ion beam bombarded plant cell walls

Ion bombardment of plant and bacterial cellular material has recently been used as a tool for the transfer of exogenous DNA macromolecules into the cell interior region. The precise mechanism that leads to the transfer of macromolecules through the cell envelope is not yet clear, however it has been observed that the ion bombardment is accompanied by the formation of “microcraters” on the cell wall, and it is possible that these features provide channels for the macromolecule transfer. Thus the nature and origin of the microcraters is of importance to understanding the DNA transfer phenomenon as well as being of fundamental interest. We report here on some scanning electron microscope observations we have made of onion skin cells that have been subjected to electron beam bombardment of sufficiently high power density to damage the cell wall. The damage seen is much less than and different from the microcraters formed subsequent to ion bombardment. We speculate that the microcraters may originate from the explosive release of gas generated in the biomaterial by ion bombardment.