Determination of oxygen profiles in agar-based gelled in vitro plant tissue culture media

Keeping account of the limited knowledge concerning the relevance of the ox ygen status of the medium during in vitro culture, a technique was elaborat ed to systematically study the oxygen concentration in gelled media. In a f irst series of experiments, the Oxygen Diffusion Rate (ODR) technique was u sed to investigate the dissolved oxygen concentration as a function of time at different depths. The results obtained demonstrated that the oxygen con centration in agar media was reduced by 80% during the heating steps includ ed in the preparation procedure. It took about one week to reach an oxygen concentration equal to 90% of the equilibrium value at a depth of 1 cm, irr espective of the brand of agar used. As the recovery of the oxygen concentr ation at various depths could be nicely modelled by Fick's law, it follows that this process is diffusion limited. In this respect, fluorescence recov ery after photobleaching (FRAP) measurements revealed that the diffusion co efficient of oxygen in gelled media was only affected to a very small exten t by the presence of up to 2% (w/v) agar. In a final experiment, explants o f Ficus benjamina were cultured on a rooting medium. As the oxygen concentr ation in the gelled medium was not significantly affected by the presence o f the biological material, it was concluded that the oxygen uptake by expla nts from gelled media is negligibly small and hence cannot be considered as being a growth-limiting factor during in vitro micropropagation.