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La diminution de la croissance vegetative observee chez nombreuses plantes, soumises au stress salin et exposees a des conditions naturelles d’ensoleillement, est souvent associee a une baisse de leur activite photosynthetique. Cependant les mecanismes de l’inhibition photosynthetique sont encore peu etudies. Le photosysteme II (PS II) est considere un des facteurs cle dans la reponse de la photosynthese des feuilles aux stress environnementaux. L’association de la lumiere et du stress salin parait avoir des effets synergetiques sur l’activite photochimique du PSII conduisant, ainsi a la photoinhibition. L’objectif de cette etude est de diagnostiquer l’effet de l’interaction lumiere- salinite sur l’activite photochimique du photosysteme II au cours de la photosynthese. Le materiel vegetal est constitue de deux varietes de mais (Zea mays L.) fourrager: Aristo et Arper . Des feuilles detachees de plantes cultivees sur milieu temoin (eau distilee), sont incubees pendant 6 heures dans des solutions salines a differentes concentrations (0, 100, 200 et 300 mM NaCl), soit en absence ou en presence de lumiere (1000 μmol m -2 s -1 ). Puis, leurs teneurs en sodium ont ete determinees. Pour verifiers’il y’aura recuperation de leur activite photochimique, d’autres feuilles qui ont ete mises a absorber du NaCl dans une solution de 300 mM a la lumiere pendant 4 heures, sont transferees dans de l’eau distillee en obscurite ou en lumiere. Les resultants montrent une stabilite du rendement quantique maximal (Fv/Fm) pour les feuilles mises a absorber du NaCl a l’obscurite.Par contre l’eclairement associe avec la salinite engender une photoinhibition qui se manifeste par une diminution du rendement quantique maximal du PSII. Cette photoinhibition, due a une accumulation excessive des ions Na+dans les tissus foliaires, est reversible. En effet, en absence d’un seul des facteurs de l’association lumiere-salinite le PSII recupere son activite photochimique. Mots Cles: fluorescence chlorophyllienne, feuillesexcisees, stress lumineux, chlorure de sodium, Zea mays English Abstract 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 activity resume. Keywords: Light stress, sodium chloride, Zea mays

The leaf-structural adaptative strategies and the possible involvement of the antioxidative system in the tolerance to salt stress were investigated in relation to leaf tissue senescence of maize. Studies were carried out with seedlings of two forage maize varieties ( Aristo and Arper ) subjected to 0, 34, 68 and 102 mM NaCl for 6 weeks under glasshouse conditions. The leaf growth, leaf water content, H 2 O 2 generation, lipid peroxidation, membranes stability index and polyphenolic compounds (total polyphenols, total flavonoids, anthocyanins and proanthocyanidins) accumulation were quantified in three leaf stages (young, mature and senescent leaves). Salt stress impacts in term of H 2 O 2 generation and lipid peroxidation were more pronounced in senescent leaves. During the stress treatment, the accumulation of the major polyphenolic compounds was higher in young leaves. A significant variability in salt response was found between both varieties. The better behaviour of Arper salt-challenged leaves compared to those of Aristo may be related to their higher water content and polyphenol accumulation mainly anthocyanins which showed to participate efficiently in restriction of oxidative damages caused by the H 2 O 2 generation.