Photoinhibition during Acclimatization of Micropropagated Spathiphyllum "Petite" Plantlets

Micropropagated Spathiphyllum "Petite" plantlets were acclimatized at low- or high-light intensities [photosynthetic photon flux density (PPFD)$100 or 300 \mu{mol} \cdot m^{-2} \cdot s^{-1}$]. During the first days chlorophyll fluorescence measurements show a partial photoinhibition of the photosynthetic apparatus, expressed by a decrease of the variable over maximal fluorescence ratio (Fv/Fm). This inhibition of Fv/Fmwas significantly higher for plants grown at high-light intensity, leading to a photooxidation of chlorophyll. Newly formed leaves were better adapted to the ex vitro climatic condition (as shown by the increase of the Fv/Fmratio) and had a higher net photosynthesis compared with in vitro formed leaves. Nevertheless, plants grown at$300 \mu mol \cdot m^{-2} \cdot s^{-1}$were photoinhibited, compared with those at$100 \mu{mol} \cdot m^{-2} \cdot m^{-2} \cdot s^{-1}$. A sudden exposure to high-light intensity of 1-, 10- or 25-d-old transplanted plants (shift in PPFD from$100 to 300 \mu mol \cdot m^{-2} \cdot s^{-1}$) gave a linear decrease of Fv/Fmover a 12-h period, which was reflected in a 50% reduction of net photosynthesis. No significant interaction between day and hour was found, indicating high-light exposure causes the same photoinhibitory effect on in vitro and ex vitro formed leaves.