OXYGEN-TRANSFER AND CULTURE CHARACTERISTICS OF SELF-IMMOBILIZED SOLANUM AVICULARE AGGREGATES

Oxygen transfer characteristics of self-immobilized Solanum aviculare cells were measured using aggregates 3.0 to 12.5 mm in diameter. Appar ent specific oxygen uptake rates in the absence of external boundary l ayers varied from 5.9 x 10(-7) to 8.5 x 10(-7) kg kg(-1) s(-1) dry wei ght, but did not decline continuously with increasing particle size. T he effective diffusivity of oxygen in deactivated aggregates increased with particle diameter, varying from 5.0 x 10(-11) to 1.0 x 10(-9) m( 2) s(-1) or between 2% and 40% of the molecular diffusivity in water a t the same temperature. Gas spaces detected in the larger aggregates w ere confined to the central core and were not distributed throughout t he tissue to facilitate Oxygen transfer. Oxygen consumption rates in t he absence of diffusional limitations were estimated using the relatio nship between the observable Thiele modulus and effectiveness factor f or zero-order reaction. The calculated results indicated severe oxygen limitations in the aggregates, but were inconsistent with the observa tion that relatively large S. aviculare aggregates contained a high fr action of viable cells and were capable of active growth and steroidal alkaloid synthesis. This work suggests that oxygen delivery is facili tated in living plant cell aggregates by mechanisms which depend on me tabolic activity and which do not function in deactivated cells. (C) 1 995 John Wiley and Sons, Inc.