Relationship between changes in ion content of leaves and chlorophyll-protein composition in cucumber under Cd and Pb stress

Hydroponically cultured cucumber plants supplied with 4 mM Fe chelated eith er with EDTA or citrate and treated with Cd (10 mu M) and Pb (10, 50 mu M) from their wone- or four-leaf stage were grown up to five-week-old age. The decrease in the chlorophyll content was the most pronounced in plants trea ted with Cd from a younger age, and in the case of Fe-citrate. The chloroph yll a/b ratio of Cd stressed plants was also significantly lowered. In late r treated plants the accumulation of chlorophyll was inhibited and the chlo rophyll a/b ratio decreased only in the vigorously growing young leaves. Pb treatment had only a slight effect on both parameters. The changes in the chlorophyll-protein pattern of thylakoids were strongly related to their ch lorophyll content but the response of each complex was different. Cd reduce d the amount of chlorophyll containing complexes in the order of photosyste m I > light-harvesting complex II > photosystem II-core, while light-harves ting complex II appeared somewhat more sensitive than photosystem I in Pb t reated plants. In accordance, a decline or blue shift of the long wavelengt h fluorescence emission band of chloroplasts was observed referring to dist urbances also in photosystem I antenna assembly. The accumulation of chloro phyll and chlorophyll-proteins did not show close relationship to the heavy metal content of leaves which was the highest in the first of the intensiv ely expanding leaves in the time of the treatment. The extraordinary sensit ivity of photosystem I, and the relative stability of photosystem II under Cd treatment were similar to the case found in iron deficient plants. Howev er, the pattern of chlorophyll content of leaf storeys of Cd treated plants rather followed the changes in their Mn content.