Physiology of Effects of Temporary Immersion Bioreactor (TIB)on Micropropagated Plantlets

Temporary Immersion Bioreactor (TIB)is an efficient tool for plant mass propagation because it increases multiplication rate and plant quality. Little knowledge is available on the ecosystem and physiological behavior of plantlets in this new technique of culture. In order to evaluate the effects of these conditions on physiological change of plantlets, the composition of headspace (CO2, O2 and ethylene)was analyzed at different moment during the whole in vitro period and during 3 hours after the immersion of plants. The evolution of the photosynthetic capacity and the main enzymatic systems related to carbon metabolism during the culture of shoots in a Temporary Immersion Bioreactor and their subsequent acclimatization were also evaluated. The maximal rate of photosynthesis (Pn), transpiration, and the activity of the following enzymes phosphoenolpyruvate carboxylase (PEPC), acid invertase (AI), pyruvate kinase (PK)and sucrose phosphate synthase (SPS)were measured every 7 days during the 21 days of elongation in TIB, and the following 42 days of acclimatization. Sucrose content in the liquid medium and in the leaves was also determined. Plantlets showed large increases in sugar and nitrogen uptake and also increases in dry weight and foliar area. Shoot growth did not totally depend on the photosynthesis process. In vitro plantlets appeared to use more nutrients in the culture medium than those from photosynthesis. TIB-derived plantlets showed a remarkable nutrient uptake indicating a higher photo-mixotrophic metabolism. The relation between morphological parameters, photosynthetic capacity of the plantlets and the carbon metabolism enzymes during both phase of the culture are integrate and discussed.