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. Fe-citrate at 10 µm or 50 µm was given with or without 10 µm 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. 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 ΔF/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 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 ΔF/F_m′ proved to be the most-rapidly reacting parameters. Iron deficiency is a key factor in Cd-induced inhibition of photosynthesis.

Iron (Fe) is an essential transition metal. Based on its redox-active nature under biological conditions, various Fe compounds serve as cofactors in redox enzymes. In plants, the photosynthetic machinery has the highest demand for Fe. In consequence, the delivery and incorporation of Fe into cofactors of the photosynthetic apparatus is the focus of Fe metabolism in leaves. Disturbance of foliar Fe homeostasis leads to impaired biosynthesis of chlorophylls and composition of the photosynthetic machinery. Nevertheless, mitochondrial function also has a significant demand for Fe. The proper incorporation of Fe into proteins and cofactors as well as a balanced intracellular Fe status in leaf cells require the ability to sense Fe, but may also rely on indirect signals that report on the physiological processes connected to Fe homeostasis. Although multiple pieces of information have been gained on Fe signalling in roots, the regulation of Fe status in leaves has not yet been clarified in detail. In this review, we give an overview on current knowledge of foliar Fe homeostasis, from the chemical forms to the allocation and sensing of Fe in leaves.

Phytoremediation is a plant based, cost effective technology to detoxify or stabilise contaminated soils. Fast growing, high biomass, perennial plants may be used not only in phytoremediation but also in energy production. Szarvasi-1 energy grass (Elymus elongatus subsp. ponticus cv. Szarvasi-1), a good candidate for this combined application, was grown in nutrient solution in order to assess its Cd, Cu, Ni, Pb and Zn accumulation and tolerance. Its shoot metal accumulation showed the order Pb < Ni < Cu ∼ Cd < Zn. In parallel with this, Pb and Ni had no or very little influence on the growth, dry matter content, chlorophyll concentration and transpiration of the plants. Cu and Cd treatment resulted in significant decreases in all these parameters that can be attributed to Fe plaque formation in the roots suggested by markedly increased Fe and Cu accumulation. This came together with decreased shoot and root Mn concentrations in both treatments while shoot Cu and Zn concentrations decreased under Cd and Cu exposure, respectively. Zn treatment had no effect or even slightly stimulated the plants. This may be due to a slight stimulation of Fe translocation and a very efficient detoxification mechanism. Based on the average 300 mg kg⁻¹ (dry mass) Zn concentration which is 0.03% of the shoot dry mass the variety is suggested to be classified as Zn accumulator.