Conifer Reproductive Biology Claire G

Conifer Reproductive Biology Claire G. Williams Conifer Reproductive Biology Claire G. Williams USA ISBN: 978-1-4020-9601-3 e-ISBN: 978-1-4020-9602-0 DOI: 10.1007/978-1-4020-9602-0 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2009927085 © Springer Science+Business Media B.V. 2009 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Cover Image: Snow and pendant cones on spruce tree (reproduced with permission of Photos.com). Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Foreword When it comes to reproduction, gymnosperms are deeply weird. Cycads and conifers have drawn out reproduction: at least 13 genera take over a year from pollination to fertilization. Since they don’t apparently have any selection mechanism by which to discriminate among pollen tubes prior to fertilization, it is natural to won- der why such a delay in reproduction is necessary. Claire Williams’ book celebrates such oddities of conifer reproduction. She has written a book that turns the context of many of these reproductive quirks into deeper questions concerning evolution. The origins of some of these questions can be traced back Wilhelm Hofmeister’s 1851 book, which detailed the revolutionary idea of alternation of generations. This alternation between diploid and haploid generations was eventually to become one of the key unifying ideas in plant evolution. Dr. Williams points out that alternation of generations in conifers shows strong divergence in the evolution of male and female gametes, as well as in the synchronicity of male and female gamete development. How are these coordinated to achieve fertilization? Books on conifer reproduction are all too rare. The only major work in the last generation was Hardev Singh’s 1978 Embryology of Gymnosperms, a book that summarized the previous century’s work. Being a book primarily about embryology, it stopped short of putting conifer reproduction in a genetic or evolutionary context. There have also been reviews in particular orders and families, but these tend to be oriented towards orchard management problems and practical concerns of seed production. There are few works that are comprehensive and yet acces- sible to graduate students and researchers. Professor Williams’ book provides new avenues to explore in our thinking. The book also comes along at a opportune moment. The last 40 years have wit- nessed many advances in our understanding of conifer reproduction. These have proven of practical value to both experimentalists and seed orchard managers. Advanced breeding programs have developed in many countries to the benefit of the forest industry. Genetically improved trees are widely planted, providing sources of fiber and timber. In addition, these breeding methodologies have spread to many developing countries. Although we are only beginning to understand some of the cell biology that controls and regulates the properties of economically important traits in trees, we have developed many practical and effective methodologies that allow us to produce seed at scale for purposes of reforestation and afforestation. v vi Foreword With such an abundance of genotypes selected and tested for various charac- teristics, it is not surprising that conifer reproduction studies are poised to enter another era. But what era is it? Conifer genomics and metabolomics are expanding; conifer proteomics is still in its infancy. It appears that the original sin of conifers is to have too much DNA. We are forced to be wait for a published genome. This is compounded by our inability to see where things are going in the future. Arabidopsis, poplar and other model plants are providing new information on herbs and trees. Turning this to our advantage rests on our scientific imagination. In this regard, Dr. Williams’ book takes stock of interesting questions for the benefit of future forest biologists and geneticists. The book works at a number of levels. It introduces conifers in their proper evolutionary context. It begins by putting a modern relic – Wollemi Pine – in perspective. From the Golden Age of conifers in the Mesozoic when they were the world’s first truly successful and widespread seed plants, Claire Williams leads us to modern conifers, including those that are rare and threatened. She then turns to reproduction, in particular of the Pinaceae. She sets the stage by describing the Bauplan of the life cycle from meiosis to mature seed. The book then changes gear when it considers the consequences of heterospory. This is of great value for train- ing graduate students and for providing researchers with new questions concerning karyotypes, large genomes, and the consequences of crossing. Generally, in the previous compendia of conifer reproduction, emphasis has been on family-by- family differences in the details of reproduction. Not since Willson and Burley’s 1983 book entitled Mate Choice in Plants has there been a book in which the effects of conifer organization on reproduction and genetics are presented as unsolved problems. From the historical perspective, many things remain as true today as when they were first unveiled. As the author writes, “Robert Brown’s (1828) discovery of the gametophyte and its multiple archegonia are more profound than he knew”. We still have little idea how these large female gametophytes regulate their own lives separately from those of the surrounding sporophyte, whether in terms of defense or signaling or regulation of development. Furthermore, we have little understanding of the female gametophyte’s role in regulating its own abortion or that of young embryos. The male side of reproduction poses other problems, starting with pollen dispersal. The description of Erdtman’s trip across the Atlantic in the 1930s during which he sampled the air for pollen provides a nice context in which to consider pollen dispersal. In this chapter, we get a fresh consideration of features that allow pine pollen to fly long distances. Synchronizing pollination, female development and fertilization in these reproductive plodders remains a great mystery. Claire Williams lays it out carefully, providing many new and testable ideas. What are the forces that converge to syn- chronize male and female development and result in pollination drop secretion? How does the female gametophyte eventually exert its influence in reproduction, given that for so long it was subsidiary to the sporophyte in all previous pollination- related events? Her years of study of events that regulate embryo development and death, particularly those due to selfing, show clearly in the later chapters on seed Foreword vii development and mating system dynamics, culminating in a thought-provoking discussion of embryo lethal systems. This is a book that should be used by researchers who want new perspectives on conifer reproduction. It is an excellent book for a graduate course or to put new life into a discussion group or journal club. Since the 1970s, there has been an explo- sion in our understanding of the details of reproduction, but it is now time to take stock and think about what this means. This book will help young and old researchers frame new questions, re-frame old ones using new genomic tools, and finally, it encourages readers to ask good questions that will contribute to our knowledge of the evolution, ecology and development of conifers. Victoria, BC, Canada Patrick von Aderkas Prologue This book on conifer reproductive biology is intended as a text supplement for plant biology courses. Knowledge of model flowering plants is expanding so fast that each new plant biology text has less written on conifers than the last. Conifer Reproductive Biology seems needed as a specialized botany reference for life science professionals, graduate students and advanced undergraduates. Its content, chosen for its relevance to those working in the life sciences including ecology, evolution, genomics, environmental sciences, genetics, forestry, conservation and even immuno- logy, is shaped by a trend towards the integrative study of conifer reproduction. Book content. Integrative reproductive biology rests on a concept put forth by Johann Goethe (1749–1832) who argued that each of the various parts of a plant – including its reproductive organs and seeds – could be understood as variations on a basic body plan. His Bauplan concept for the Die Urpflanze (“the original plant”)1 enables one to predict selection space for plant morphology or to infer plant forms no longer living. Although the Bauplan concept was first adopted as a central tenet in metazoan biology, the seed plant biology community is only now adopting this useful concept. One must consider the possibility that conifers might not share a Bauplan distinct from other seed plants. After all, the grouping of conifers is a taxonomic classification based on the absence of a carpel and other angiosperm reproductive characters. An integrative biology perspective is provided here for the few conifer lineages that survived after the Mesozoic era. Conifers and other gymnosperms are the only living links to early seed plant reproduction so Conifer Reproductive Biology has evolutionary relevance. This perspective includes the Bauplan concept. It will come into sharper focus now once the huge conifer genomes are completely sequenced but until then, seed plant biology (inclusive of conifers) will continue to move through a reductionist phase where whole-organism studies are less valued. But such reduction- ism is only temporary. Next will be the need to integrate all sources of information, 1 The Bauplan concept was published in 1790 by Johann Wolfgang von Goethe in his Metamorphose der Pflanzen as cited by Kaplan, D.

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