IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Abstract

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.

ACKNOWLEDGMENTS

This work was supported by grants AGR97-1177 from the Comision Inter- ministerial de Ciencia y Tecnologia to A.A. and AIR3-CT94-1973 from the Commission of European Communities to J.A. M.Z. was supported by a Master fellowship from the International Center for Advanced Agronomical Mediterranean Studies-Instituto Agronómico Mediterráneo de Zaragoza (CIHEAM-IAMZ). We thank Aurora Poc for excellent technical assistance in the growing of the plants.