Effect of microprojectile bombardment parameters and osmotic treatment on particle penetration and tissue damage in transiently transformed cultured immature maize (Zea mays L) embryos

Immature maize (Zea mays L.) embryos of the tropical inbred line Cat-100-6, plated in callus induction medium for short periods, were used to study the effect of microprojectile bombardment parameters and osmotic treatment on the transformation of embryogenic competent cells. Somatic embryogenesis in this material arose from sub-epidermal cell clusters located at the third or deeper cell layer. Experiments were carried out focusing on the transformation of these cell clusters following microprojectile bombardment. Physical conditions such as particle delivering method, particle size, helium pressure and target distance were analyzed in factorial experiments. The best condition which permitted the transformation of embryogenic cell clusters at relatively high frequency was found to cause deleterious tissue damage because of the bombardment at high pressure and short target distance. Tissue damage as successfully prevented by the addition of mannitol in the culture medium before and after bombardment. Copyright (C) 1996 Elsevier Science Ireland Ltd.