Transgenic plants of lettuce cultivar (cv.) 'South Bay' were produced by using Agrobacterium tumefaciens vectors containing the /3-glucuronidase (GUS) reporter gene and the NPT II gene for kanamycin resistance as a selectable marker. High frequency of transformation, based on kanamycin resistance and assays for GUS expression, was obtained with 24 to 72-h-old cotyledon explants cocultivated for 48 h with Agrobacterium tumefaciens. After the cocultivation period, the explants were placed in selection medium containing 50 or 100mgl -I of kanamycin, 100mg1-1 cefotaxime and 500mg1-1 carbenicillin for 10 days. Surviving explants were transferred every 14 days on shoot elongation medium. Progenies of R 0 plants demonstrated linked monogenic segregation for kanamycin resistance and GUS activity.

Somatic embryos of Ipomoea batatas Lam. (sweet potato cv. 'White Star') were produced in an airlift bioreactor. This work describes the optimization of the embryogenic system on semisolid medium, followed by transfer of the system to liquid cultures and ultimately to the airlift bioreactor. The physiological age of embryogenic callus influenced the number and overall morphology of the embryo population in both semisolid and liquid medium. Maximum mature embryo production (35 embryos 10 mg-~ inoculum) was obtained from six-week-old callus at 30°C. Somatic embryogenesis occurred in liquid cultures containing 20 mM NH4NO3 and 30 mM KC1. Globular embryos formed and continued development in suspension producing viable, mature cotyledonary embryos by day 14. Embryo formation and development was limited in the bioreactor. Although shear stress was responsible for some embryogenic damage, the effect of purging the system with fresh air needed to be investigated. To isolate aeration effects from shear stress effects, atmospheric determinations were performed on shaker flask cultures. Initially the gas composition within the Erlenmeyer headspace was that of room air. Ethylene increased to a maximum of 6.4 ppm (day 16), maximum CO2, 21.2%, was also evident on day 16, and oxygen was depleted to a minimum of 8.1% by day 14. Purging the cultures with fresh air reduced the number of embryos formed; however, they were significantly longer than those formed in closed flasks. The gas response model of Ipomoea batatas will enable atmosphere replenishment in the bioreactor mimicking that of the shaker flask environment. Once the damaging effects of shear stress have been overcome, the regulation of bioreactor gasses should allow somatic embryo formation in the bioreactor comparable to that in shaker flasks.