PHOTOINHIBITION DURING ACCLIMATIZATION OF MICROPROPAGATED SPATHIPHYLLUM PETITE PLANTLETS

Micropropagated Spathiphyllum ''Petite'' plantlets were acclimatized a t low- or high-light intensities [photosynthetic photon flux density ( PPFD) 100 or 300 mu mol . m(-2). s(-1)]. During the first days chlorop hyll fluorescence measurements show a partial photoinhibition of the p hotosynthetic apparatus, expressed by a decrease of the variable over maximal fluorescence ratio (F-v/F-m). This inhibition of F-v/F-m was s ignificantly higher for plants grown at high-light intensity, leading to a photooxidation of chlorophyll. Newly formed leaves were better ad apted to the ex vitro climatic condition (as shown by the increase of the F-v/F-m ratio) and had a higher net photosynthesis compared with i n vitro formed leaves. Nevertheless, plants grown at 300 mu mol . m(-2 ). s(-1) were photoinhibited, compared with those at 100 mu mol . m(-2 ). s(-1). A sudden exposure to high-light intensity of 1-, 10- or 25-d -old transplanted plants (shift in PPFD from 100 to 300 mu mol . m(-2) . s(-1)) gave a linear decrease of F-v/F-m over a 12-h period, which w as reflected in a 50% reduction of net photosynthesis. No significant interaction between day and hour was found, indicating high-light expo sure causes the same photoinhibitory effect on in vitro and ex vitro f ormed leaves.