Photosynthesis and carbon metabolism in leaves formed prior and during ex vitro acclimatization of micropropagated plants

During the first days after transplanting micropropagated plants to greenhouse conditions, in vitro leaves are the only source to cover metabolic demands and to sustain plants' adaptation and regrowth. However, the way these leaves act can differ depending on plant species and in vitro conditions. Here, we describe two main groups. In Calathea the in vitro leaves function as storage organs, from which the accumulated reserves (glucose, fructose) are consumed during the first days after transfer, until new leaves appear; these in vitro leaves never become fully autotrophic. On the contrary, in Spathiphyllum in vitro leaves are photosynthetically competent and normal source-sink relations are observed. Any surplus in photoassimilates at the end of the photoperiod is converted into starch. Three weeks after transfer, those leaves start to senesce and newly developed leaves become the main source of carbohydrates. In both plant species, higher photosynthetic activities are measured once new leaves are fully developed. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.