Dynamics of metabolic responses to iron deficiency in sugar beet roots

This study presents information on the dynamics of sugar beet (Beta vulgaris L.) root metabolic responses to Fe deficiency. Four days after Fe withdrawal from the nutrient solution, the concentration of reduced glutathione (GSH) and the activities of ferric chelate reductase (FC-R, E.C. 1.6.99.13) and ascorbate peroxidase (APX, E.C. 1.11.1.11) showed marked differences with the control values. The differences in root fresh weight, the concentrations of ascorbate (Asc) and soluble proteins, and proton release rates by roots became more prominent after the first week. Time course kinetics of FC-R activity and proton extrusion showed induction maxima, followed by rapid declines with the progress of Fe deficiency. The time courses of root Asc and GSH concentrations showed gradual increases with the advancement of Fe deficiency suggesting that plant responses to Fe deficiency stress may include a shift in the redox balance inside the root cells towards more reduced state. Data imply that an alternative Asc-dependent Fe reduction may become important with the advancement of Fe deficiency stress, when FC-R activity is declining. The time course of APX activity reveals that it could be a sensitive indicator of the initial changes in the plant Fe nutritional status.Work supported by grant BOS2001-2343 from the Spanish Ministry of Science and Technology to J.A. T.Z. was supported by a sabbatical grant (SAB95-0551) from the Spanish Ministry of Science and Education.Peer Reviewe