Impact of iron supply on the kinetics of recovery of photosynthesis in Cd-stressed poplar (Populus glauca).
OBJECTIVE
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 microm or 50 microm was given with or without 10 microm 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.


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 F690/F740 ratio) and functional (elevation of CO2 fixation activity and DeltaF/Fm') recovery of the photosynthetic machinery was detected. Cd-induced, light-stress-related changes in non-photochemical quenching, activity of the xanthophyll cycle, and the F440/F520 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 DeltaF/Fm' proved to be the most-rapidly reacting parameters.


CONCLUSIONS
Iron deficiency is a key factor in Cd-induced inhibition of photosynthesis.
Solti
Adám
A
Department of Plant Physiology and Molecular Plant Biology, Eötvös University, Pázmány P. sétány 1/C Budapest, 1117 Hungary. sadambio@elte.hu
Gáspár
László
L
Mészáros
Ilona
I
Szigeti
Zoltán
Z
Lévai
László
L
Sárvári
Eva
E