IN-VITRO CO2 ENRICHMENT OF CAM ORCHID PLANTLETS

Increased growth of an in vitro-propagated CAM orchid hybrid Mokara 'W hite' was obtained using a novel method of COP enrichment in an optimi zed photoautotrophic open system compared with the conventional closed system of culture. The optimization process for the open system invol ved the manipulation of external CO2 concentrations (0.03%, 1% and 10% ), sucrose requirements, light intensities (80 and 200 mu mol m(-2) s( -1)) and the venting of headspace ethylene from the culture vessels. T he physiological basis for increased growth in these CAM orchid plantl ets after three months was attributed to the direct effects of elevate d CO2 resulting in higher CAM activity for the plantlets and to the el evated CO2 present in the system which might interact with the ethylen e present thereby reducing the inhibition of growth of plantlets due t o ethylene.