Optimisation of DNA transfer and transientβ-glucuronidase expression in electroporated maize (Zea mays L.) microspores.

The ability to deliver free DNA into microspores of a highly androgenic hybrid of maize was assessed by electroporation, using a square wave pulse discharge apparatus. The electroporation medium was chosen according to its ability to maintain a high level of regeneration. Nuclease activities were analyzed and were inhibited by the addition of 100 mM KNO3 and MgSO4 in the electroporation medium. Seven expression vectors withUid A as the reporter gene under the control of cauliflower mosaic virus 35S, Lat 52-7, Zmg 13, Emu, Ubiq-1, Al, or Actl promoters were tested in relation to the level of ß-glucuronidase expression in maize microspores. The highest level of expression was obtained when theUid A gene was driven by the Actl promoter. Therefore, this vector was further used to define optimal conditions leading to highest levels of ß-glucuronidase expression. The parameters determined in this study could provide an ideal starting point for the obtention of transgenic maize plants from electroporated microspores.