Relationship of iron deficiency and the altered thylakoid development in Cd treated poplar plants

Abstract

The reasons of Cd inhibition of photosynthesis, particularly that of chlorophyll-protein organisation, have not been revealed yet. As Cd is known to influence the ion household of plants (particularly Fe metabolism), which may play important role in the biogenesis and functioning of the photosynthetic apparatus, we investigated their relationship. Poplar plants were grown hydroponically on 10m M Fe-citrate or Fe-EDTA up to four-leaf stage and then treated with 10m M Cd(NO3)2 or by withdrawal of the Fe supply up to seven-leaf stage. Chlorophyll-protein pattern, ion- and carotenoid contents were determined by Deriphat PAGE, TXRF and HPLC. Parallel with leaf chlorosis related to the strength of stress, the amount of Fe content decreased in Cd treated and Fe-EDTA-grown iron deficient plants. The lack of Fe deficiency symptoms in Fe-citrate-grown plants could be correlated with the differential effects of chelators on the root adsorption, uptake and translocation of Fe. A parallel decrease in the Mn content was also seen, but only in Cd treated plants. Lowering of the Chl a/b ratio was due to a stronger decrease in the amount of PSI than that of LHCII in Cd treated leaves. PSII core turned out to be the most stable complex. Decrease in qP and rise of qN and the total carotenoid and VAZ content was observed. Concerning the differential accumulation of complexes the stabilisation of PSI, which is especially dependent on Fe availability, may be inhibited by Cd induced physiological Fe-deficiency. However, compositional changes in thylakoids, i.e. stability of PSII (dissipative PSII centres) and decreased accumulation of LHCII, can also be explained by regulatory mechanisms working under photoinhibitory conditions due to inhibition of photosynthesis by Cd induced Fe and/or Mn deficiency. Increase in qN and VAZ content refers to such type of acclimation.