Temporary immersion bioreactors are an efficient tool for plant mass propagation because they increase multiplication rate and plant quality. Little knowledge is available on the ecosystem and physiological behavior of plantlets when using this new culture technique. In order to evaluate the effects of the conditions on physiological change of pineapple plantlets, a factorial experiment was conducted, where axillary clusters were cultured under two levels of photosynthetic photon flux (PPF): 80 µmol m−2 s−1 (low) and 225 µmol m−2 s−1 (high), using two culture methods (conventional micropropagation in liquid medium and a temporary immersion bioreactor) during the elongation phase. CO2 concentration in the headspace volume container was measured during a whole cycle of temporary immersion (3 h). At the time before the next immersion period, the levels of CO2 increased significantly to 14 171 µmol mol−1 at high PPF. The maximal photosynthetic rate as well as the maximum quantum yield of photosystem II were low for plantlets cultivated in the temporary immersion bioreactor at high PPF. However, these plantlets showed large increases in sugar and nitrogen uptake and also increases in dry weight and foliar area. These results indicate that shoot growth did not totally depend on the photosynthesis process. In vitro pineapple plantlets appeared to use more nutrients in the culture medium than those from photosynthesis. In summary, temporary immersion bioreactor-derived plantlets showed remarkable nutrient uptake, indicating a higher photo-mixotrophic metabolism.
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Vol. 39 • No. 6