Abstract
BackgroundIron deficiency induces in Strategy I plants physiological, biochemical and molecular modifications capable to increase iron uptake from the rhizosphere. This effort needs a reorganization of metabolic pathways to efficiently sustain activities linked to the acquisition of iron; in fact, carbohydrates and the energetic metabolism has been shown to be involved in these responses. The aim of this work was to find both a confirmation of the already expected change in the enzyme concentrations induced in cucumber root tissue in response to iron deficiency as well as to find new insights on the involvement of other pathways.ResultsThe proteome pattern of soluble cytosolic proteins extracted from roots was obtained by 2-DE. Of about two thousand spots found, only those showing at least a two-fold increase or decrease in the concentration were considered for subsequent identification by mass spectrometry. Fifty-seven proteins showed significant changes, and 44 of them were identified. Twenty-one of them were increased in quantity, whereas 23 were decreased in quantity. Most of the increased proteins belong to glycolysis and nitrogen metabolism in agreement with the biochemical evidence. On the other hand, the proteins being decreased belong to the metabolism of sucrose and complex structural carbohydrates and to structural proteins.ConclusionsThe new available techniques allow to cast new light on the mechanisms involved in the changes occurring in plants under iron deficiency. The data obtained from this proteomic study confirm the metabolic changes occurring in cucumber as a response to Fe deficiency. Two main conclusions may be drawn. The first one is the confirmation of the increase in the glycolytic flux and in the anaerobic metabolism to sustain the energetic effort the Fe-deficient plants must undertake. The second conclusion is, on one hand, the decrease in the amount of enzymes linked to the biosynthesis of complex carbohydrates of the cell wall, and, on the other hand, the increase in enzymes linked to the turnover of proteins.
Highlights
Iron deficiency induces in Strategy I plants physiological, biochemical and molecular modifications capable to increase iron uptake from the rhizosphere
The phosphoenolpyruvate carboxylase (PEPC) activity has been shown to increase several times under Fe deficiency [21,22]. This enzyme is very important in the economy of the cell, since it can accomplish several tasks: (i), by consuming PEP it increases the rate of glycolysis, releasing the negative allosteric control exerted on phosphofructo kinase-1 (PFK-1) and aldolase by this phosphorylated compound [23]; (ii), it contributes to the intracellular pH-stat mechanisms [24] and (iii), it forms organic acids, in particular malate and citrate, that may play an important role in the transport of iron through the xylem to the leaf mesophyll [25,26]
Implication of metabolism has been inferred from the microarray analysis performed on Fe-starved Arabidopsis plants [28], in which it was shown that the levels of several transcripts encoding enzymes of these metabolic pathways were increased
Summary
Iron deficiency induces in Strategy I plants physiological, biochemical and molecular modifications capable to increase iron uptake from the rhizosphere This effort needs a reorganization of metabolic pathways to efficiently sustain activities linked to the acquisition of iron; carbohydrates and the energetic metabolism has been shown to be involved in these responses. The phosphoenolpyruvate carboxylase (PEPC) activity has been shown to increase several times under Fe deficiency [21,22] This enzyme is very important in the economy of the cell, since it can accomplish several tasks: (i), by consuming PEP it increases the rate of glycolysis, releasing the negative allosteric control exerted on phosphofructo kinase-1 (PFK-1) and aldolase by this phosphorylated compound [23]; (ii), it contributes to the intracellular pH-stat mechanisms [24] and (iii), it forms organic acids, in particular malate and citrate, that may play an important role in the transport of iron through the xylem to the leaf mesophyll [25,26]. Concerning plant iron nutrition, two recent studies have analysed by 2-DE the proteome of wild-type tomato and its fer mutant [29,30] grown under Fe deficiency, to identify to what extent the transcription factor FER influences the accumulation of Fe-regulated protein, while another one analysed the changes in proteomic and metabolic profiles occurring in sugar beet root tips in response to Fe deficiency and resupply [31]
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