Background and Aims Cadmium (Cd) causes Fe-deficiency-like symptoms in plants, and
strongly inhibits photosynthesis. To clarify the importance of Cd- induced Fe deficiency
in Cd effects on photosynthesis, the recovery processes were studied by supplying
excess Fe after the Cd symptoms had developed. Methods Fe-citrate at 10 mu M or 50
mu M was given with or without 10 mu M Cd(NO3)(2) to hydroponically cultured poplars
(Populus glauca 'Kopeczkii') with characteristic Cd symptoms. Ion, chlorophyll and
pigment contents, amount of photosynthetic pigment-protein complexes, chlorophyll
fluorescence and carbon assimilation were measured together with the mapping of healing
processes by fluorescence imaging. Key Results In regenerated leaves, the iron content
increased significantly, while the Cd content did not decrease. As a result, the structural
(increase in the amount of photosynthetic pigments and pigment-protein complexes,
decrease in the F-690/F-740 ratio) and functional (elevation of CO2 fixation activity
and Delta F/F-m') recovery of the photosynthetic machinery was detected. Cd-induced,
light-stress-related changes in non-photochemical quenching, activity of the xanthophyll
cycle, and the F-440/F-520 ratio were also normalized. Imaging the changes in chlorophyll
fluorescence, the recovery started from the parts adjacent to the veins and gradually
extended to the interveinal parts. Kinetically, the rate of recovery depended greatly
on the extent of the Fe supply, and chlorophyll a/b ratio and Delta F/Fm' proved to
be the most-rapidly reacting parameters. Conclusions Iron deficiency is a key factor
in Cd- induced inhibition of photosynthesis.
