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Copper Accumulation in Citrus Roots and Desorption with Acid¹

ABSTRACT

Root accumulation of ⁰⁴Cu from labelled Cu(NO₃)₂ in intact ‘Mandarin Orange’ (Citrus reticulata) seedlings had a constant rate for the first 15 min and then became curvilinear for periods from 15 to 180 min, when the ambient solution contained 0.6 ppm Cu. Over a 60-min contact time uptake of Cu was linear for ambient Cu concentration range from 0.3 to 1.2 ppm. Extraction of ⁶⁴Cu in roots by 0.1N HCl was linearly proportional to total root Cu and was 95% complete after 28 min. Colloidal phosphate reduced ⁶⁴Cu accumulation in the roots by 12%. In roots of ‘Sour Orange’ (C. aurantium) seedlings grown in solution culture and in groves Cu was located in thin sections by ferrocyanide staining. Concentration of Cu occurred in the exodermis, endodermis, and pericycle cells. Electromicrographs of citrus roots suffering from Cu toxicity showed irregular deformation of cell walls in xylem vessels. In such cases roots became club shaped as root elongation ceased. Reactions of Cu with protein are suggested as mechanisms for Cu accumulation in roots.

¹ Contribution from Soils Department, Institute of Food & Agriculture, University of Florida, Agr. Exp. Sta. Journal Series no. 3658, taken in part from the Ph.D. dissertation of the senior author. Presented before Div. S-4, Soil Science Society of America, Aug. 27, 1970, at Tucson, Ariz.

² Formerly Graduate Assistant and then Soils Specialist, University of Illinois, and Professor of Soils, respectively.

Received for publication August 20, 1970. Accepted for publication May 21, 1971.