A method for estimating the oxygen availability in plant cell cultures grown in stationary liquid media (e.g. many protoplast cultures) was developed. The method is based on short-term measurements of respiration rate versus oxygen concentration on a sample of cells, suspended in liquid media. From such data it is possible to estimate the oxygen concentration at the bottom of a stagnant liquid culture, by calculating the amount of oxygen reaching the cells by diffusion. As an example, rape (Brassica napus L. cv. Omega) hypocotyl protoplasts were grown with different oxygen concentrations at the site of the cells, obtained by varying the cell density, the height of the liquid layer and the oxygen content of the gas phase. The number of surviving calli was positively correlated with the estimated oxygen availability in the range between 60 and 350/~M 02, below 60 ~M all cells died. This indicates that oxygen availability can be a limiting factor in the range usually encountered in protoplast cultures, and that the method can be useful when designing optimal growth conditions for stationary cultures of plant cells.
Abbreviations: C 1-bulk oxygen concentration in agitated medium, Co-oxygen concentration in medium at the gas-liquid interface, in equilibrium with the gas, C x -oxygen concentration at cell level, D -diffusion constant of oxygen in water, KLa -oxygen transfer rate, 1 -height of liquid above cells, n -number of cells per ml, R x -respiration rate per cell