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Agrobacterium tumefaciens-mediated genetic transformation and the regeneration of transgenic plants was achieved in Hevea brasiliensis. Immature anther-derived calli were used to develop transgenic plants. These calli were co-cultured with A. tumefaciens harboring a plasmid vector containing the H. brasiliensis superoxide dismutase gene (HbSOD) under the control of the CaMV 35S promoter. The beta-glucuronidase gene (uidA) was used for screening and the neomycin phosphotransferase gene (nptII) was used for selection of the transformed calli. Factors such as co-cultivation time, co-cultivation media and kanamycin concentration were assessed to establish optimal conditions for the selection of transformed callus lines. Transformed calli surviving on medium containing 300 mg l(-1) kanamycin showed a strong GUS-positive reaction. Somatic embryos were then regenerated from these transgenic calli on MS2 medium containing 2.0 mg l(-1) spermine and 0.1 mg l(-1) abscisic acid. Mature embryos were germinated and developed into plantlets on MS4 medium supplemented with 0.2 mg l(-1) gibberellic acid, 0.2 mg l(-1) kinetin (KIN) and 0.1 mg l(-1) indole-3-acetic acid. A transformation frequency of 4% was achieved. The morphology of the transgenic plants was similar to that of untransformed plants. Histochemical GUS assay revealed the expression of the uidA gene in embryos as well as leaves of transgenic plants. The presence of the uidA, nptII and HbSOD genes in the Hevea genome was confirmed by polymerase chain reaction amplification and genomic Southern blot hybridization analyses.

A gene transfer system developed for walnut (Juglans regia L.) was successfully applied to pecan (Carya illinoensis [Wang] K. Koch). Repetitively embryogenic somatic embryos derived from open-pollinated seed of 'Elliott', 'Wichita', and 'Schley' were co-cultivated with Agrobacterium strain EHA 101/pCGN 7001, which contains marker genes for beta-glucuronidase activity and resistance to kanamycin. Several modifications of the standard walnut transformation techniques were tested, including a lower concentration of kanamycin and a modified induction medium, but these treatments had no measurable effect on efficiency of transformation. Nineteen of the 764 viable inoculated embryos produced transgenic subclones; 13 of these were from the line 'Elliott'6, 3 from 'Schley'5/3, and 3 from 'Wichita'9. Transgenic embryos of 'Wichita'9 germinated most readily and three subclones were successfully micropropagated. Three transgenic plants of one of these subclones were obtained by grafting the tissue cultured shoots to seedling pecan rootstock in the greenhouse. Gene insertion, initially detected by GUS activity, was confirmed by detection of integrated T-DNA sequences using Southern analysis.

The effects of the plant signal molecule acetosyringone (AS) and the osmoprotectant betaine phosphate (BP) have been examined for their ability to increase the transformation efficiency of Agrobacterium tumefaciens (At), C58C1::pGV3850 harboring the binary vector pKIWI105. This binary plasmid encodes the β-glucuronidase (GUS) gene and was previously shown to be expressed exclusively in plant tissues. Bacteria were grown in one of two previously reported virulence induction media (MS20 and SIM) for 5h and GUS activity was measured fluorimetrically in individual 6 week old leaf discs as a quantitative measure of stable transformation events. Bacteria induced in MS20 supplemented with AS (0.1 mM) and BP (1 mM) showed a significant increase in GUS activity as compared to media containing AS or BP added singly or control media lacking the supplements. The effects of another osmoprotectant proline (1 mM) could replace the beneficial effects of betaine. No significant difference was observed among treatments with respect to the two induction media.

AnAgrobacterium-mediated gene transfer system which relies on repetitive embryogenesis to regenerate transgenic walnut plants has been made more efficient by using a more virulent strain ofAgrobacterium and vectors containing genes for both kanamycin resistance and beta-glucuronidase (GUS) activity to facilitate early screening and selection. Two plasmids (pCGN7001 and pCGN7314) introduced individually into the disarmedAgrobacterium host strain EHA101 were used as inoculum. Embryos maintained on medium containing 100 mg/l kanamycin after co-cultivation produced more transformed secondary embryos than embryos maintained on kanamycin-free medium. Of the 186 GUS-positive secondary embryo lines identified, 70% were regenerated from 3 out of 16 primary embryos inoculated with EHA101/pCGN7314 and grown on kanamycin- containing medium, 28% from 4 out of 17 primary embryos inoculated with EHA101/ pCGN7001 and grown on kanamycin medium, and 2% from one out of 13 primary embryos inoculated with EHA101/pCGN7001 but not exposed to kanamycin. Because kanamycin inhibits but does not completely block new embryo formation in controls, identification of transformants formerly required repetitive selection on kanamycin for several months. Introduction of the GUS marker gene allowed positive identification of transformant secondary embryos as early as 5-6 weeks after inoculation. DNA analysis of a representative subset of lines (n=13) derived from secondary embryos confirmed transformation and provided evidence for multiple insertion events in single inoculated primary embryos.