Chimeric genes containing the coding sequence for bacterial chloramphenicol acetyl transferase (CAT) have been introduced by electroporation into maize protoplasts (Black Mexican Sweet) and transient expression monitored by enzyme assays. Levels of CAT expression were enhanced 12-fold and 20-fold respectively by the inclusion of maize alcohol dehydrogenase-1 introns 2 and 6 in the chimeric construct. This enhancement was seen when the intron was placed within the 5' translated region but not when it was located upstream of the promoter or within the 3' untranslated region. Deletion of exon sequences adjacent to intron 2 abolished its ability to mediate enhancement of CAT gene expression. Northern analysis of protoplasts electroporated with intron constructs revealed elevated levels of CAT mRNA. However, this elevation was insufficient to account for the increased enzyme activity. One explanation of these results is that splicing affects both the quantity and quality of mRNA.

Genetically transformed maize plants were obtained from protoplasts treated with recombinant DNA. Protoplasts that were digested from embryogenic cell suspension cultures of maize inbred A188 were combined with plasmid DNA containing a gene coding for neomycin phosphotransferase (NPT II) next to the 35S promoter region of cauliflower mosaic virus. A high voltage electrical pulse was applied to the protoplasts, which were then grown on filters placed over feeder layers of maize suspension cells (Black Mexican Sweet) and selected for growth in the presence of kanamycin. Selected cell lines showed NPT II activity. Plants were regenerated from transformed cell lines and grown to maturity. Southern analysis of DNA extracted from callus and plants indicated the presence of the NPT II gene.

Two reactions generate NADH in the glyoxysomes of germinating oil seeds. Isolated glyoxysomes accumulate I mol ofNADH for each mol of acetyl CoA generated during ,f-oxidation of fatty acids (5). Additionally, the conversion of 2 mol of acetate to I mol of succinate in the glyoxylate cycle requires the oxidation of malate to OAA2 and, thus, the production of I mol of NADH (2). Inasmuch as isolated intact mitochondria, but not glyoxysomes, are capable of reoxidizing NADH, it was concluded that the NADH produced in the glyoxysomes is oxidized by the mitochondria (1, 5, 13).However, the presence of highly active GOT in glyoxysomes and mitochondria suggests that aspartate and malate may be utilized in a shuttle system transferring reducing equivalents generated from NADH between the organelles (1,4). In this paper, we have investigated this possibility further. Shuttling systems of this type have been described in other organelles (3,6,8, 18

No abstract

No abstract