EFFET DE L’INTERACTION LUMIERE-SALINITE SUR L’ACTIVITE DU PHOTOSYSTEME II DES FEUILLES EXCISEES DE MAÏS

The decline in growth observed in many plants, subjected to salt stress and exposed to sunlight conditions, is often associated with a decrease in their photosynthetic activity. No clear mechanisms of the inhibited photosynthesis have emerged since photosystem II (PS II) is considered to play a key role in the response of leaf photosynthesis to environmental perturbations. The combination of light and salt stress appears to have synergistic effects on the photochemical activity of PSII driving, and to photoinhibition. The objective of this study was to evaluate the reversible effect of salinity and light interaction on maximal quantum efficiency of photosystem II (Fv/Fm.). In this experiment, detached leaves of two forage maize (Zea mays L.) varieties, Aristo and Arper were placed during 6 hours in solutions of different concentrations of NaCl (0, 100, 200 and 300 mM) and subjected to light (1000 μmol m-2 s-1) or obscurity. Then, their contents of sodium were determined. In order to verify the photo-inhibition reversibility, other leaves which were incubated in a solution of 300 Mm NaCl, during 4 hours were transferred in distilled water and also subjected to light or to obscurity. Results indicate that leaves which had been put to absorb NaCl in obscurity showed no change in maximal efficiency of PSII (Fv/Fm). Nevertheless, light treatment associated with salinity generates a photo-inhibition of PSII manifested by a significant decrease in maximal efficiency of PSII. This photo-inhibition, due to an excessive accumulation of sodium in leaves, is reversible. It is quite sufficient to eliminate only one factor of the association light-salinity for the PSII activityresume.