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Foreword "Molecular Sensory Physiology" is the youngest among the biological subdisciplines, which are devoted to the understanding of biological activities in terms of chemical structure and bonding. In contrast to metabolic functions, which are concerned with a turnover or transfer of matter, and be it matter as small in size and weight as tone electrons, the new discipline is characterized by the transfer of "signals", the question being: What are the signals made of and how are they transmitted? The present volume is concerned with light signals and their transformation. The first step is the localization and identification of the light acceptor. The difficulties connected with this aim are mostly pertinent to the fact that signal transfer activity can only be followed in the whole organism, and only in rare cases on a subcellular level. Furthermore, the acceptor molecules (chromophores) are frequently not unique or specific in their signal transfer activity, but catalyze known metabolic functions in other places (environments). Thus, we must distinguish the possibilities of finding known holoproteins with hitherto unassigned functions or, on the other hand, known cofactors exhibiting new functions when bound by a new protein. Third, we may have in the new function a slightly modified cofactor. In any case, since we cannot follow the signal transfer activity down to a cell-free system, we must reverse our way of thinking and feed the whole organism with a modified acceptor in order to trace down the signal transformation into "response" and, subsequently, explain the response in terms of chemical structure. In other words: The routine of "natural product chemistry" and its refined methods of structural microanalysis might not apply. Instead, new ways of "bioorganic" imagination applied to suitable mutants of active organisms might lead to success. The difficulties in betraying whole cells with a modified acceptor are enormous, but can be overcome by an intense cooperation between biologists and organic chemists. This cooperation is hampered by "linguistic" problems, which this volume might help to overcome. P. Hemmerich Contents Physiological Bluelight Reception W. Schmidt . . . . . . . . . . . . . . . . . . . . . . . . . . . Flavins as Photoreceptor Pigments for Behavioral Responses M. J. Doughty, B. Diehn . . . . . . . . . . . . . . . . . . . . . 45 Sensory Physiology of Phycomyces Blakesleeanus V. E. A. Russo, P. Galland . . . . . . . . . . . . . . . . . . . . . 71 Light Perception and Sensory Transduction in Photosynthetic Prokaryotes W. Nultsch, D.-P. H~ider . . . . . . . . . . . . . . . . . . . . . 111 Author-Index Volumes 1 4 1 141 . . . . . . . . . . . . . . . . . . . . Physiological Bluelight Reception Wemer S c h m i d t * Universit~it Konstanz, Fachbereich Biologie, Postfach 7733, D-7750 Konstanz, Federal Republic of Germany Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.4 2,4.1 2.4.2 2.4.3 Phototropism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Dosage Response Relationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Spectral Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Action Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modification of Absorption Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phototropism Requires a Lateral Light Gradient . . . . . . . . . . . . . . . . . . . . . . . The Role of Auxin in Phototropism o