EFFECTS OF MICROPROJECTILE BOMBARDMENT ON EMBRYOGENIC SUSPENSION CELL-CULTURES OF MAIZE (ZEA-MAYS L) USED FOR GENETIC-TRANSFORMATION

We have investigated the interaction between tungsten and gold micropr ojectiles with suspension-culture cells of maize used for genetic tran sformation. Particle size measurements were evaluated before and after DNA precipitation to determine mean particle size and the effect of D NA precipitation on particle aggregation. Following particle bombardme nt, metal foils were examined by scanning electron microscopy to visua lize dispersion of individual particles and aggregates. Particle penet ration into suspension-culture cell clusters was examined in paraffin- embedded bombarded cells serially sectioned and viewed with light micr oscopy and by energy dispersive X-ray microanalysis. Acridine-orange-s tained bombarded cells were examined to observe cellular response to p article penetration. Transient expression of reporter genes C1 and B a nd GUS, (beta-glucuronidase) were used to assess effects of particle b ombardment on embryogenic cell types. Autoradiographic analysis of the transformable suspension cell culture SC82 (see Gordon-Kamm et al. 19 90, Plant Cell 2, 603-618) was conducted to evaluate the S-phase and m itotic indices in embryogenic and nonembryogenic cells throughout a su bculture passage and in response to DNA/particle delivery. The results of these investigations are discussed relative to cytodifferentiation of suspension cell clusters and recovery of transformed clonal sector s.