Résumé
Citrus plants originate from southeastern Asia, in a large area with various climates characterized by a broad range of temperatures. Temperature is assumed to be a key factor in Citrus species adaptation and diversification. In a field experiment, the tolerance of the three fundamental Citrus species (C. medica -citron-, C. reticulata -mandarin- and C. maxima -pummelo-) and Fortunella japonica -kumquat- to photooxidative stress caused by seasonal climatic changes was evaluated on adult trees by measuring net photosynthesis (Pnet), stomatal conductance (Gs), maximum photosynthesis (Pmax) and chlorophyll fluorescence (Fv/Fm). In addition, seasonal changes in oxidative status, antioxidant enzymes and antioxidant metabolites were monitored. Mandarin and pummelo appeared to be the most tolerant, showing the lowest down-regulation of photosynthetic parameters, and the lowest accumulation of oxidized compounds associated with efficiency of their antioxidant system. Kumquat showed intermediate behaviour, with a large diminution of photosynthetic parameters and marked accumulation of hydrogen peroxide, whereas the malondialdehyde content remained low, with a strong induction of glutathione synthesis. Finally, citron appeared to be the most sensitive genotype with a marked decrease in photosynthetic performance, the largest accumulation of oxidative parameters, insufficient induction of antioxidant enzymes and down-regulation of ascorbate and glutathione synthesis. (Texte integral)