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Some Observations on the Bleaching Effect of Ethylenediaminetetraacetic Acid on Green Barley Leaves ^1,2

^a Medical Microbiology and Immunology Unit and the Naval Biological Laboratory of the School of Public Health, University of California, Berkeley, California 94720

Green barley leaves (Hordeum vulgaris) floated on the surface of 0.05 M ethylenediamine disodium tetraacetate, EDTA-2Na, pH 7.0 and exposed to light (5000 lux) at 25° exhibited a marked bleaching (EDTA-bleaching) visible to the naked eye and paralleled by a striking reduction in content of chlorophylls a and b. This loss of color did not occur in controls which were treated with H₂O instead of EDTA (water controls). In darkness the leaves in the water controls were bleached while EDTA-treated leaves retained all their color.

EDTA bleaching was observed only in intact leaves. When leaves were boiled EDTA protected their pigment against photodecomposition. Without EDTA boiled leaves were bleached completely in light.

When intact green leaves which had been floated on water and exposed to light for 48 hr were treated with boiling ethanol or acetone, the chlorophylls extracted by this procedure did not undergo bleaching if EDTA were present in solution. Under these conditions a green fine grain precipitate formed which was insoluble in ethanol or acetone and was stable in light or darkness.

EDTA bleaching of green barley leaves was inhibited by KCN, and by the addition of casein hydrolysate.

² A part of this paper was presented before the Annual Meetings of Plant Physiologists at the University of Massachusetts, Amherst, Massachusetts, August 20 to 23, 1968(5).