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 gr eenhouse conditions, in vitro leaves are the only source to cover meta bolic 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 photoperio d is converted into starch. Three weeks after transfer, those leaves s tart to senesce and newly developed leaves become the main source of c arbohydrates. In both plant species, higher photosynthetic activities are measured once new leaves are fully developed. (C) 1998 Elsevier Sc ience Ireland Ltd. All rights reserved.