Metabolic Adjustment under Fe Deficiency in Roots of Dicotyledonous Plants

Iron (Fe) deficiency is a yield-limiting factor for a variety of field crops grown incalcareous and alkaline soils across the world. Iron, albeit abundant, is often not solubleand therefore unavailable for root uptake. Thus, the study of processes regulating Feuptake and translocation in plant is crucial to acquire useful knowledge to obtainbiofortified plants and to improve the nutritional value of plant food that would have adramatic positive impact on human health. Most of the plants (Strategy I) reduces soilFe(III) to Fe(II) through a plasma membrane Fe(III)-chelate reductase, prior to takes upFe2+ through a specific transporter (IRT1). However, the response to Fe deficiency stressin these plants is by far more complex than the simple activation of the reduction-basedmechanism. In several Strategy I plants studied so far there is an associated increase inthe activity of a plasma membrane H+-ATPase which actively extrudes protons necessaryfor decreasing the rhizospheric pH and generating the electrochemical proton gradient todrive Fe uptake. Along with these activities it has been found an involvement of themetabolism to sustain the production of the reducing equivalents [NAD(P)H] and ATP.In particular, the activity of phosphoenolpyruvate carboxylase is increased several fold.The rate of carbohydrate catabolism is also increased under these conditions and theactivity of several glycolytic enzymes has been shown to be enhanced, as well.Furthermore, other metabolic pathways and free cytosolic enzymatic activities areincreased during Fe deficiency, such as some cytosolic NAD(P)+-dependentdehydrogenases belonging to the oxidative pentose phosphate pathway. Some of theseincreased activities are associated with an enhanced expression of the correspondinggenes. In this chapter we will focus on the metabolic changes which follow the primaryevents involved in plant Fe uptake. The comprehension of how plants are able to adjust their metabolism under Fe starvation allows to found some inherent traits whoseactivation makes plants more efficient in the acquisition of this essential nutrient.