Chemical warfare between plants and their herbivores and pathogens was first brought to our attention by the publication 25 years ago of the paper by Fraenkel in Science. There, he pointed out that most plants have similar nutritional characteristics so that the selection of plants by insect herbivores must depend on the relative toxicity of secondary compounds. This led, rather gradually, to a host of papers on plant-herbivore interactions. More or less at the same time, insect physiologists and ecologists were starting to realise the importance of chemical communi cation systems in determining sexual and other characteristics of insect behaviour. Nine years ago the Phytochemical Society of North America published their Symposium on 'Biochemical Interaction Between Plants and Insects' in which the plant apparency theory was expounded by both Paul Feeny and Rex Cates and David Rhoades. This stated that plants which are apparent usually contain secondary components which reduce digestibility (tannins and lignins) while ephemeral plants have more toxic, and perhaps less costly, compounds such as alkaloids. These papers stimulated much research on biochemical ecology. The recognition of the importance of the biochemical factors in such interactions is not just of scientific interest. It is vitally important in programs for the production of new varieties of cultivated plants, especially in tropical countries where about one-third or more of the crops are lost to predation or disease."

Chemical warfare between plants and their herbivores and pathogens was first brought to our attention by the publication 25 years ago of the paper by Fraenkel in Science. There, he pointed out that most plants have similar nutritional characteristics so that the selection of plants by insect herbivores must depend on the relative toxicity of secondary compounds. This led, rather gradually, to a host of papers on plant-herbivore interactions. More or less at the same time, insect physiologists and ecologists were starting to realise the importance of chemical communi cation systems in determining sexual and other characteristics of insect behaviour. Nine years ago the Phytochemical Society of North America published their Symposium on 'Biochemical Interaction Between Plants and Insects' in which the plant apparency theory was expounded by both Paul Feeny and Rex Cates and David Rhoades. This stated that plants which are apparent usually contain secondary components which reduce digestibility (tannins and lignins) while ephemeral plants have more toxic, and perhaps less costly, compounds such as alkaloids. These papers stimulated much research on biochemical ecology. The recognition of the importance of the biochemical factors in such interactions is not just of scientific interest. It is vitally important in programs for the production of new varieties of cultivated plants, especially in tropical countries where about one-third or more of the crops are lost to predation or disease."

This volume is based on papers presented by invited speakers at a symposium entitled "Plant Nitrogen Metabolism" held in conjunction with the 28th Annual Meeting of the Phytochemical Society of North America. The meeting took place on the campus of the University of Iowa at Iowa City during June 26-30, 1988, and attracted 110 participants from 11 countries. The goal of the symposium was to trace the pathway by which nitrogen passes from soil and atmosphere into both primary and secondary nitrogenous metabolites, focusing upon areas which were felt to be most rapidly expanding. From nodulines (nodule specific proteins) and GS/GOGAT mutants to sugar mimics (polyhydroxyalkaloids) and herbicide inhibitors of amino acid metabolism, research in nitrogen metabolism has expanded into areas barely envisioned only a few years ago. Both the nitrogen specialist and the general plant biochemist will be pleased by the range of topics covered here. Following an overview in Chapter 1 of plant nitrogen metabolism, the remaining chapters are loosely organized into three groups. Chapters 2-6 deal primarily with the biochemistry and molecular biology of nitrogen assimilation and transport, Chapters 7-9 with amino acid metabolism, and Chapters 10-12 with secondary metabolites.

This volume contains the invited papers presented as a symposium of The Phytochemical Society of North America which met for its annual meeting at the Asilomar Conference Center, Pacific Grove, California on June 12-16, 1985. The topic of the symposium, "The Shikimic Acid Pathway - Recent Advances," was especially appropriate for this, the Silver Anniversary of the Society because of the many natural products derived from that pathway. The organizers of the symposium recognized that it would not be possible to cover all groups of compounds derived from shikimic acid and therefore decided to omit any detailed discussion of flavonoid compounds and lignin. Research in these two areas has been the subject of several recent symposiums and/or published volumes. By omitting these topics, it was possible to devote more attention to other, equally interesting products derived from the shikimate pathway. Each chapter in the volume authoritat vely speaks for itself on an important topic. However, the reader is invited to enjoy the lead chapter by Ulrich Weiss who describes his role in the research on the shikimate pathway during 1952/53. We are grateful to Dr. Weiss for this charming account of his work carried out in the laboratory of Dr. B. D. Davis during that period. Those who attended the Silver Anniversary Meeting were privileged to hear Dr. Gestur Johnson reminisce about the founding of the Society, initially called the Plant Phenolics Group of North America. At the annual banquet R. Horwitz also shared with us some recollections of Dr.

The influence of compounds in the environment on the chemistry of plants is a topic which has economic and scientific implications of global importance. Selected presentations in this symposium covered several topics within this immense field, inclusive of air, soil, and aquatic sources of the compounds. As demonstrated in Chapter 4 by O'Keeffe et al. we have not restricted the discussion solely to negative aspects of anthropogenic compounds. Nor could we begin to cover comprehensively all major classes of environmental compounds in the air, soil or water that may have an effect on the phytochemistry of plants. Our intent was to focus on some of the timely and well publicized environmental constituents such as ozone, sulfur dioxide, acid rain, and others, to provide an authoritative publication specifically related to environ mental modifications of plant chemistry. The concept of this symposium originated with the Executive Committee of the Phytochemical Society of North America in 1983. It was brought to fruition during July 13-17, 1986 on the campus of the University of Maryland at the annual meeting of the PSNA through the efforts of the Symposium Committee composed of James A. Saunders and Lynn Kosak-Channing. Financial support for this meeting was provided by the Phytochemical Society of North America, as well as by generous contributions from E. I. du Pont de Nemours & Company and the U. S. Department of Agriculture. The Organizing Committee, consisting of J. A. Saunders (Chair), J. M. Gillespie, L. Kosak-Channing, E. H. Lee, J. P."