Helen A. Stafford - Böcker

Throughout the tropics, vast areas of rainforest and other biologically diverse lands are being cleared for agricultural or related uses. Rainforests, the most dramatic example of tropical habitat destrucLion, are estimated to be disappearing at the rate of up to 20.4 million hectares per year world-wide (based on FAO estimates; see World Resources 1990-1991, Oxford University Press)­ more than 2% of the total area covered by tropical rainforests per year. Destruction of these complex habitats results in the irreversible loss of both plant and animal diversity, and dramatically illustraLes the need to investigate these threatened species for potentially useful constituents-especially the identification and characterization of novel biologically-active phytochemicals with pharmacologiical and/or pesticidal properties. This volume is based on papers presented by invited speakers at an international symposium entitled "Phytochemical POlential of Tropical Plants: held in conjunction with the second joint meeting of the Phytochemical nd Societies of Europe and North America, as well as the 32 annual meeting of the latter society. The meeting was held at the Deauville Hotel, Miami Beach, Florida, USA from August 8-12,1992. One hundred and twenty-five participants from more than 20 countries attended this meeting.

This comprehensive review discusses the biosynthesis and catabolism of flavonoids and their regulation in plants. This interesting work approaches the subject matter from both a historical and methodological point of view. It places emphasis on key regulatory enzymic steps in the two pathways leading to the flavonoid basic units as well as the overall pathway within the flavonoid group. This special volume focuses on the known cell-free enzymology at the C15 level, as well as isotopic tracer studies involving the still unknown enzymic steps. This up-to-date text is an excellent resource for all plant physiologists, biological chemists, phytochemists and chemical ecologists.

In this volume of Recent Advances in Phytochmistry you will find a record of the pioneering attempts of plant biochemists and molecular biologists to modify the patterns of secondary metabolism in plants, as presented at the 33rd annual meeting of the Phytochemical Society of North America, in Asilomar, California, on June 27 -July I, 1993. The studies described here represent a marriage of the newest of technologies with one of the oldest human activities, exploitation of plant chemistry. They also represent the beginning of a new era of phytochemical research, an era that will undoubtedly begin to provide answers to some of the long-standing questions that have absorbed plant biochemists for the past century. There is, for instance, a common deflating experience to which every worker in the area of plant secondary metabolism can probably relate. After hearing about the latest research findings regarding some aspect of remarkable compound "X", someone in the audience finally directs the inevitable question at the hapless speaker. "Tell me, is anything known as to the biological role of compound "X" in the plant?" The answer, in most cases, must be "essentially nothing"! This is a frustrating scenario for both the speaker and the audience, since the very fact that a complex biosynthetic pathway remains encoded in a plant genome points to an associated selective advantage. The problem is that establishing the nature and scale of that advantage is a very complex task.

This volume contains reviews presented at the 31 st annual meeting of the Phytochemical Society of North America, held at Colorado State University in Fort Collins, Colorado on June 22-26, 1991. This symposium, entitled Phenolic Metabolism in Plants, celebrated the origin of this society as the Plant Phenolics Group of North America; the first symposium, entitled Biochemistry of Plant Phenolic Substances, was also held at Fort Collins from August 31 to September 1, 1961. A brief history of the Society is presented in Chapter 12 by Stewart Brown, one of the original founders of the Society. We dedicate this volume to Hans Grisebach, 1926-1990, Professor of Biochemistry at the Biologisches Institut II, Freiburg, Germany, where he headed for many years a laboratory responsible for major advances in the area of phenolic metabolism; this will be self evident from the numerous bibliographical references cited in the literature for papers by his Freiburg group from about 1958 until now, and subsequently by former students and colla­ borators. His impact on the data reviewed in this volume will testify to this.

This series of lectures was delivered at the 29th meeting of the Phytochemical Society of North America, held at the University of British Columbia in Vancouver, B. C. , Canada on June 16th-20th, 1989. Topics concerning terpenoids, consisting of isoprene units, are now so numerous that a judicious selection for a relatively limited symposium was difficult. We were able to assemble, however, a potpourri of reviews on topical areas of terpenoid chemistry, biochemistry and biology, by scientists who are making exciting contributions and whose work points the way to significant future research. Because of the importance of terpenoids in the life of plants, and indeed in all living organisms, a periodical review of the mevalonic acid pathway and of the subsequent biochemical events leading to the biosynthesis of isoprenoids needs no justification. Life, as we know it, would not be possible without the ability of living organisms to employ this metabolic sequence which proceeds from condensations of three molecules of acetyl-CoA and terminates with the elaboration of the terpenoid precursors, isopentenyl pyrophosphate and dimethylallyl pyrophosphate. In addition to producing obviously essential compounds that are partially or completely of isoprenoid origin (Fig. 1), such as hormones, photosynthetic pigments, compounds involved in electron transport in respiration and in photosynthesis, oxidative enzymes and membrane components, plants elaborate thousands of novel terpenoids, many of which do not as yet have identifiable physiological, biochemical or even ecological roles, e. g. the cardenolides, ecdysones or saponins.

This volume contains reviews which are based on a symposium, given th at the 30 meeting of The Phytochemical Society of North America, held at Laval University in Quebec City, Canada on August 11-15, 1990. During the past two decades, there have been major new developments in methods which can be applied toward the isolation, separation and structure determination of complex natural products. Therefore, the topic of this symposium, "Modem Phytochemical Methods", is a very timely one. The organizers of the symposium recognized that it would not be possible to cover in detail all new advances in phytochemical methodology. It was therefore decided to emphasize general reviews on recent developments of major separation techniques such as high performance liquid chromatography as well as supercritical fluid chromato­ graphy. In addition, advances in commonly used structure determination methods, mainly NMR and MS, are reviewed. Other topics include methodo­ logies of micro-sampling for isolation and analysis of trichome constituents as well as recent breakthroughs on biosynthetic studies of monoterpenes using "enriched" basal cells of trichomes. The volume concludes with a review of quantitative structure-activity relationship (QSAR) studies of biologically active natural products. In Chapter I, K. Hostettmann and his colleagues give a general review of recent developments in the separation of natural products with major emphasis on preparative separations of biologically active plant constituents. The authors present a comparison of droplet countercurrent chromatography (OCCC) with the highly rapid and more versatile centrifugal partition chromatography (CPC).