Iron is an essential element for plant metabolism because of its redox properties. Its long distance and intracellular trafficking require specialized proteins and low molecular mass chelates because of its insolubility and toxicity in presence of oxygen. Iron deficiency induces various morphological and biochemical changes. They include root hair morphogenesis, differentiation of rhizoder-ma1 cells into transfer cells, yellowing of leaves and ultrastructural disorganisation of chloroplasts and mitochondria, as well as increased synthesis of organic acids and phenolics, and activation of root systems responsible for an enhanced iron uptake capacity. Upon iron resupply, these alterations disappeared within few days and a transient accumulation of the iron storage protein ferritin in the plastids is one of the early events in this process. Iron excess can also occur in plants where it elicits an oxidative stress leading to necrotic spots in the leaves. Induction of ferritin synthesis is again an early event of the plant response to this iron toxicity. Plant hormones such as auxin, abscisic acid and ethylene, as well as reactive oxygen intermediates play an important role in the transduction pathways, allowing plants to respond to these iron-deficiency and excess stresses. Similarities and differences among the various mechanisms responsible for iron uptake and storage in mammals, higher plants and yeast are outlined. Relationships between iron and copper metabolism are also indicated. plant / root / chloroplast / iron / ferritinIron traffk in non-stressed plants

The consequences of iron deficiency and iron re-supply were evaluated during the early stages of growth and development of young maize plantlets grown hydroponically in the ahsence of iron. Various parameters, such as fresh and dry weights, and the concentration of chlorophylls, iron, copper, manganese, calcium, magnesium and potassium in leaves, were measured at various times during the first 15 d of culture. Ten-day-old maize plantlets grown without iron displayed severe alterations, with a 50% decrease in iron and chlorophyll concentrations in leaves, and serious impairments in mitochondria and chloroplast ultrastructure. In contrast, neither leaf nor root growth, nor other mineral concentrations other than iron were significantly affected at this stage of development. In an attempt to characterize proteins potentially involved in iron nutrition or the adaptative response to iron starvation, comparative 2D-gel electrophoretic analysis of polypeptides was carried out on soluble and memhrane fractions prepared from leaves and roots of iron-deficient and iron-sufficient 10-d-old maize plantlets. Two polypeptides (11 and 17 kDa, pi of about 6-8) from the micro.sonial iraction of leaves were found to be repressed under iron-deticient conditions. Some other polypeptides were found to be induced in microsomal fractions either from roots or leaves. Significant variations in the concentration of most of these polypeptides were observed from one experiment to another. It can be concluded from this study that, at this early stage of maize vegetative growth and development, molecular variations induced by iron deficiency do not affect major house-keeping proteins, but probably affect very specific events depending on low abundance proteins.

The effects of iron deficiency on cell culture growth, cell respiration, mitochondrial oxidative properties, and the eledron transport chain were studied with suspension-cultured sycamore (Acer pseudoplatanus 1.) cells. lron deprivation considerably decreased the initial growth rates and limited the maximum density of the cells. Under these conditions, the cells remained swollen throughout their growth. The absence of iron led to a steady decline in the uncoupled rate of Oz consumption. When the uncoupled rate of 0 2 uptake closely approximated the respiratory rate, the cells began to collapse. At this stage, the leve1 of all the cytochromes and eledron paramagnetic resonance-detedable Fe-S clusters of the mitochondrial inner membrane were dramatically decreased. Nevertheless, it appeared from substrate oxidation measurements that this overall depletion in iron-containing components solely disturbed the fundioning of complex II, whereas neither complexes I, 111, or IV, nor the machinery involved in ATP synthesis, was apparently impaired in iron-deficient mitochondria. However, our results suggest that the impairment of complex II resulted in a strong reduction of the overall capacity of the mitochondrial electron transport chain, which was responsible for determining the rate of endogenous respiration in sycamore cells. Finally, this situation led to a depletion of various energy metabolites that could contribute to the premature cell death.The great need for iron in biological systems is a consequence of its irreplaceable role as a catalyst for many intracellular reactions. An important example is mitochondrial electron transfer via Cyts and iron-sulfur (Fe-S) proteins. Thus, Ohnishi et al. (1971) demonstrated that low iron content in the growth medium of yeast cultures significantly decreased the mitochondrial content of many EPR-detectable Fe-S clusters. In addition, severe iron deficiency results in a large decrease in the activity of mitochondrial respiratory chain dehydrogenases (succinate-and NADH-ubiquinone oxidoreductases) in skeletal muscle mitochondria (Maguire et al., 1982;Ackrell et al., 1984), leading to a decrease in mitochondrial respiratory activity. Likewise, Cartier et al. turbation of respiration in plants by iron deficiency. The concepts of iron function in cell respiration are being explored both in animal systems and in yeast, providing an important reference point. Nevertheless, crucial differences in the impact of iron deficiency on cell respiration between plants and animals may exist and thus we must not hastily embrace the findings using mammalian cells until key experiments on plant cells have been completed.In this context, we undertook the present study to analyze the effects of iron deficiency on plant cell culture growth and respiratory metabolism. Plant cell-suspension cultures rapidly generate large amounts of cell material that offer a useful tool for studying plant cell physiology. MATERIALS AND METHODS Biological MaterialSycamore (Acer pseudoplatanus L.) cells were grown at ...