Transformed petunia, tobacco, and tomato plants have been produced by means of a novel leaf disk transformation-regeneration method. Surface-sterilized leaf disks were inoculated with an Agrobacterium tumefaciens strain containing a modified tumor-inducing plasmid (in which the phytohormone biosynthetic genes from transferred DNA had been deleted and replaced with a chimeric gene for kanamycin resistance) and cultured for 2 days. The leaf disks were then transferred to selective medium containing kanamycin. Shoot regeneration occurred within 2 to 4 weeks, and transformants were confirmed by their ability to form roots in medium containing kanamycin. This method for producing transformed plants combines gene transfer, plant regeneration, and effective selection for transformants into a single process and should be applicable to plant species that can be infected by Agrobacterium and regenerated from leaf explants.

Glyphosate (N‐phosphonomethyl‐glycine) is the active ingredient the nonselective herbicide Roundup. The sensitivity of crop plants to glyphosate has limited its in‐season use as a postemergence herbicide. The extension of the use of Roundup herbicide to allow in‐season application in major crops such as soybeans [Glycine max (L.) Merr.] would provide new weed control options for farmers. A glyphosate‐tolerant soybean line, 40‐3‐2, was obtained through expression of the bacterial 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSP synthase, EPSPS) enzyme from Agrobacterium sp. strain CP4. Line 40‐3‐2 is highly tolerant to glyphosate, showing no visual injury after application of up to 1.68 kg acid equivalent (a.e.) ha−1 of glyphosate under field conditions. Molecular characterization studies determined that the single genetic insert in line 40‐3‐2 contains only a portion of the cauliflower mosaic virus 35S promoter (P‐E35S), the Petunia hybrida EPSPS chloroplast transit peptide (CTP), the CP4 EPSPS gene, and a portion of the 3' nontranslated region of the nopaline synthase gene (NOS 3') terminator. Inheritance studies have shown that the transgene behaves as a single dominant gene and is stable over several generations.

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Transgenic petunia plants containing an altered (Leu22----Arg22) mouse dihydrofolate reductase gene fused to the cauliflower mosiac virus 35S (CaMV 35S) promoter and nopaline synthase (nos) polyadenylation site were obtained by transforming petunia leaf disks with an Agrobacterium tumefaciens strain carrying the chimeric gene. Transformants were directly selected for and rooted on medium containing 1 microM methotrexate (MTX). The chimeric gene was present in the regenerated plants at one to three copies and produced the expected 950-nucleotide-long transcript based on Southern and Northern hybridization analyses, respectively. Leaf pieces from the regenerated transgenic plants were able to form callus when cultured on medium containing 1 microM MTX and were able to incorporate 32P into high-molecular-weight DNA in the presence of greater than 100 microM MTX, thus demonstrating that the chimeric mouse dhfr gene was fully functional and useful as a selectable marker in plant transformation experiments. To date, this is the first report of successful expression of a vertebrate gene in transformed plant cells.

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(4,7, 26). In apple, the optimum conditions for stratification, or after-ripening as it is often called (14), are exposure to 5°C (14) for approximately 60 d (17).The actual mechanism of low temperature release from dormancy is not known. One hypothesis is that ABA functions as a germination inhibitor and GA3 functions as a germination promoter, and the degree or depth of dormancy is a result of the ratio of the two (2, 24). GA3 levels increase during stratification (24). In hazel seeds, exogenous application of GA3 substitutes for stratification. Following such application, RNA synthesis increases as a result of increased RNA polymerase activity and DNA template availability (8, 9) indicating that release from dormancy involves gene expression (25). Excised pear embryos synthesize nucleic acids due to stratification without GA3 application (12). Application of ABA to pear embryos decreases synthesis of specific RNA fractions (11) and changes the embryo's nucleotide composition (10). While the in vitro translational capacity of polyribosomes ' Journal Paper No. 9192 of the Purdue University Agricultural Experiment Station. This paper is part of the M.S. thesis of D. A. E.

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