RESPONSES OF “NEWHALL” ORANGE TREES TO IRON DEFICIENCY IN HYDROPONICS: EFFECTS ON LEAF CHLOROPHYLL, PHOTOSYNTHETIC EFFICIENCY, AND ROOT FERRIC CHELATE REDUCTASE ACTIVITY

Abstract

Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10, or 20 μM iron (Fe), with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 μM Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.

ACKNOWLEDGMENTS

This work was supported by the European Commission-funded AIR3-CT94-1973 Project to E.A.F. and J.A., and by the Portuguese Praxis XXI program, Project 3/3.2/HORT/2160/95, to A. de V. and E.A.F. We thank Pedro Ferreira for excellent technical assistance. Thanks are given to Anunciación Abadía, Yolanda Gogorcena and Fermín Morales for reading the manuscript and providing helpful comments.