Impact of moderate Fe excess under Cd stress on the photosynthetic performance of poplar (Populus jacquemontiana var. glauca cv. Kopeczkii).

Cadmium interference with Fe nutrition has a strong impact on the development and efficiency of the photosynthetic apparatus. To shed more light on the interaction between Fe and Cd, it was studied how iron given in moderate excess under Cd stress affects the development and functioning of chlorophyll-protein complexes. Poplar plants grown in hydroponics up to four-leaf stage were treated with 10 μM Cd(NO₃)₂ in the presence of 50 μM Fe([III])-citrate as iron supply (5xFe + Cad) for two weeks. Though leaf area growth was inhibited similarly to that of Cad (10 μM Cd(NO₃)₂ + 10 μM Fe([III])-citrate) plants, chlorophyll content, ¹⁴CO₂ fixation and quenching parameters calculated from PAM fluorescence induction measurements were control-like in 5xFe+Cad leaves. Increased chloroplast iron content (measured photometrically by the bathophenanthroline disulfonate method) without changes in the iron and cadmium content of leaves (determined by inductively coupled plasma mass spectrometry) pointed out that a key factor in the observed protection of photosynthesis is the iron-excess-induced redistribution of iron in the leaf. However, the chlorophyll a/b ratio and the chlorophyll-protein pattern obtained by Deriphat PAGE remained similar to that of Cad leaves. The decreased amount of PSII core and PSI in mature and developing leaves, respectively, refers to developmental stage-dependent remodelling of thylakoids in the presence of Cd. The results underline not only the beneficial effect of iron excess under Cd stress, but also refer to the importance of a proper Fe/Cd ratio and light environment to avoid its possible harmful effects.
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