OPTIMIZATION OF DNA TRANSFER AND TRANSIENT BETA-GLUCURONIDASE EXPRESSION IN ELECTROPORATED MAIZE (ZEA-MAYS L) MICROSPORES

The ability to deliver free DNA into microspores of a highly androgeni c hybrid of maize was assessed by electroporation, using a square wave pulse discharge apparatus. The electroporation medium was chosen acco rding to its ability to maintain a high level of regeneration. Nucleas e activities were analyzed and were inhibited by the addition of 100 m M KNO3 and MgSO4 in the electroporation medium. Seven expression vecto rs with Uid A as the reporter gene under the control of cauliflower mo saic virus 35S, Lat 52-7, Zmg 13, Emu, Ubiq-1, Al, or Act1 promoters w ere tested in relation to the level of beta-glucuronidase expression i n maize microspores. The highest level of expression was obtained when the Uid A gene was driven by the Act1 promoter. Therefore, this vecto r was further used to define optimal conditions leading to highest lev els of beta-glucuronidase expression. The parameters determined in thi s study could provide an ideal starting point for the obtention of tra nsgenic maize plants from electroporated microspores.