ENHANCEMENT OF SOMATIC EMBRYOGENESIS OF IPOMOEA-BATATAS IN SOLID CULTURES AND PRODUCTION OF MATURE SOMATIC EMBRYOS IN LIQUID CULTURES FOR APPLICATION TO A BIOREACTOR PRODUCTION SYSTEM

Somatic embryos of Ipomoea batatas Lam. (sweet potato cv. 'White Star' ) were produced in an airlift bioreactor. This work describes the opti mization of the embryogenic system on semisolid medium, followed by tr ansfer 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 semiso lid and liquid medium. Maximum mature embryo production (35 embryos 10 mg(-1) inoculum) was obtained from six-week-old callus at 30 degrees C. Somatic embryogenesis occurred in liquid cultures containing 20 mM NH4NO3 and 30 mM KCl. Globular embryos formed and continued developmen t in suspension producing viable, mature cotyledonary embryos by day 1 4. Embryo formation and development was limited in the bioreactor. Alt hough shear stress was responsible for some embryogenic damage, the ef fect of purging the system with fresh air needed to be investigated. T o isolate aeration effects from shear stress effects, atmospheric dete rminations were performed on shaker flask cultures. Initially the gas composition within the Erlenmeyer headspace was that of room air. Ethy lene increased to a maximum of 6.4 ppm (day 16), maximum CO2, 21.2%, w as 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 fo rmed in closed flasks. The gas response model of Ipomoea batatas will enable atmosphere replenishment in the bioreactor mimicking that of th e shaker flask environment. Once the damaging effects of shear stress have been overcome, the regulation of bioreactor gasses should allow s omatic embryo formation in the bioreactor comparable to that in shaker flasks.