Effects of in vivo copper treatment on the photosynthetic apparatus of two Triticum durum cultivars with different stress sensitivity

The effect of copper on the photosynthetic apparatus of two cultivars of durum wheal (Triticum durum cvs Adamello and Ofanto) with different sensitivity to drought and nickel stress were investigated, Plants were grown in nutrient solution or in nutrient solution further supplemented with CuSO4 to achieve final concentrations of 3.6 mu M and 20 mu M Cu. Several fluorescence analyses were performed, in presence or absence of DCMU, and with varying light intensities. Furthermore, light and electron microscopic investigations were carried out. In vivo treatment using 3.6 mu M Cu produced a marked reduction in growth of the Cu-treated plants, but only mild effects on the fluorescence-related parameters. The Cu-induced reduction in the area above the fluorescence induction curve and in the time needed to reach the maximum of chlorophyll fluorescence (F-max) were more pronounced. These results favour the hypothesis that under such conditions copper affects photosynthesis mainly in an indirect way, causing a slowing down of the electron transport as a consequence of the reduced requirement for photosynthesis products. The morphological analyses corroborate this hy pothesis, showing toxic effects on the chloroplast structure due to Cu treatment. The differences between the two cultivars were not as pronounced as reported in the case of nickel or drought stresses; nevertheless, cv. Ofanto seemed to be less sensitive also to Cu stress than cv. Adamello.