Gaba, V., Department of Plant Genetics, Weizmann Institute of Science, Rehovot, 76100, Israel
Black, M., Department of Biology, King's College London, Kensington Campus, Campden Hill Road, London, W8 7AH, United Kingdom

Abstract— Problems concerning the interpretation of interactions of higher plant photomorphogenetic receptors are discussed. The theory that action of a blue light photoreceptor serves only to maintain responsiveness to phytochrome (Responsiveness Theory) is demonstrated to be unable to be properly tested with present techniques. This theory is also unable to explain experimental results any better than an alternative theory that a blue light photoreceptor may require the presence of the active form of phytochrome to express its activity (Presence Theory). This tatter theory is also incapable of being fully tested. There does not appear to be an adequate current theory to explain photoreceptor interactions. Other issues discussed include the use of displacement transducers in growth studies, the induction of phytochrome‐type responses by blue light, and the relative importance of the photoreceptors. New data are introduced on the effect of blue light in the end‐of‐day growth response to phytochrome of the light‐grown Cucumis sativus L. hypocotyl, and on the light equivalence principle in the same species. Copyright © 1987, Wiley Blackwell. All rights reserved