Transient transformation of maize tissues by microparticle bombardment

Transient transformation of maize coleoptiles with the β-glucuronidase gene was achieved with a particle gun built by us essentially according to the concept of Klein et al. (Nature, 327 (1987) 70–73). Either tungsten or gold particles were used to transform coleoptiles. Transformed blue cells were found in different cell layers and occasionally in as deep as the 8th layer. A transformation efficiency of up to 2% was obtained when the gene was in plasmid pAI 1GUS driven by the alcohol dehydrogenase promoter plus the intron 1. The 35S promoter of cauliflower mosaic virus (plasmid pBI221) was ten times less efficient. Other maize tissues like immature embryos, leaf basal segments and cell suspensions were also transformed but at lower rates. The time course of the histochemical reaction for the β-glucuronidase activity showed that the number of transformed blue cells detected increased up to 72 h of starting the reaction. It is concluded that transformation of maize coleoptiles with the particle gun is a good method for testing gene expression in transient systems.