Fuchs, S., Department of Chemical Immunology, Weizman Institute of Science, P.O.Box 26, Rehovot, Israel
Haimovich, J., Department of Chemical Immunology, Weizman Institute of Science, P.O.Box 26, Rehovot, Israel
Fuchs, Y., Department of Fruit and Vegetable Storage, Volcani Institute for Agricultural Research, Rehovot, Israel

Specific antibodies to two plant hormones, namely indole‐3‐acetic acid and gibberellic acid, were producd in rabbits which were immunized with conjugates of either hormone to hemolocyanin. The Specific antiboddies obtained were used for assaying the hormones by several immunological assays. The most sensitive assay reported in this paper, for the determination of indole‐3‐acetic acid and gibberellic acid, is the inhibition of inactivation of modifed bacteriphage. For this assay conjugates of either hormone with bacteriophage T4 were prepared and characterized. Such chemically modified bacteriophahges were completely inactivated by the respective specific antiserum and this inactivation was inhibiteid by the free hormone. The specificity of the antibodies produced was tested by a series of cross‐reactions. There was no immunological cross‐reaction between the two hormones which can, therefore, be determined independently. However, antibodies to indole‐3‐acetic acid cross‐reacted with chemically related compounds such as indoelcetyl‐ɛ‐amino carporic acid, tryptamine and truyptophan. The immunological specificity of different gibberellins tested was found to bne in good correlation with the biological specificity. Copyright © 1971, Wiley Blackwell. All rights reserved