Physiology and biochemistry of seeds in relation to germination

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<ul><li><p>Book review </p><p>J. D. Bewley &amp; M. Black. Physiology and Biochem- istry of Seeds in Relation to Germination. In two vols. No. 1: Development, germination, and growth. Corrected printing. 1983. XI + 306 pp., 122 figs. Springer. Verlag, Berlin-Heidelberg-New York. ISBN 3-540-08274-3. Price DM97.-; approx. US $ 38.50. </p><p>This book is a corrected printing of Vol. 1, first published in 1978. It is a comprehensive and critical account of the physiology and biochemistry of seed development, germination and early seedling growth. Each of the 7 chapters is followed by a list of general and specific references. A list of plants mentioned in the text, an author index and a sub- ject index are provided at the end of the book. </p><p>Chapter 1 tells us how to define and measure germination. A seed is defined as germinated upon emergence of the radicle from the seedcoat, and I recommend this definition. The merits of several formulae devised for determining a numerical value of germination are analyzed. </p><p>In Chapter 2 seed structure and amount, chemi- cal structure, histology and localization of food reserves in cells of gymnosperms and angiosperms are discussed. </p><p>Chapter 3 discusses the development of seeds of angiosperms and gymnosperms (by the way, the only extant gymnosperms with motile sperm are Gingko and the cycads), storage and biosynthesis of reserves and roles of hormones in seed develop- ment. Ecologists studying carbon allocation in plants will find some of the information relevant to their research. </p><p>Chapter 4 deals with water uptake by seeds. Wa- </p><p>Vegetatio 57, 115-119 (1984). Dr W. Junk Publishers, Dordrecht. Printed in the Netherlands. </p><p>ter uptake is determined by the physical properties and water content of the substrate and by factors inherent to the seed, including presence or absence of mucilage in the seedcoat, topography of the seedcoat and size of the seed. </p><p>Chapter 5 covers cellar processes of germination and growth, including respiration, development of mitochondrial activity and ATP synthesis, synthe- sis and utilization of NADH and NADPH and the mechanism of DNA, RNA and protein synthesis. (The biochemistry of dormancy per se is covered in Vol. 2 of this two-volume set.) </p><p>Chapter 6 is on the post-germination mobiliza- tion phyte (of gymnosperms). Particular attention is given to the role of the aleurone layer in mobiliz- ing endosperm reserves of cereals, mobilization of reserves in mannan-containing seeds of legumes and the conversion of fatty acids to sugars via fl-ox- idation and the glycolate pathway. A section is included on the integration of the mobilization pro- cesses. </p><p>Processes controlling the mobilization of re- serves is the subject of chapter 7. Considerable at- tention is given to the role of gibberellic acid (GA) in stimulating de novo synthesis of t~-amylase in the barley aleurone layer. However, GA also causes the release of several other enzymes from aleurone lay- ers. It is not yet clear how mobilization of reserves is regulated in non-cereal seeds. </p><p>I suspect that seeds are not phylogenetically or habitat constrained at the biochemical level, just as they are not constrained at the whole seed level in dormancy mechanisms. Further, since seeds of spe- cies that are widely separated phylogenetically or that grow in different habitats show similarities in </p></li><li><p>116 </p><p>dormancy mechanisms at the whole seed level, 'convergence' also is expected at the biochemical level. In Chapter 6, we learn that breakdown of reserves is more similar between endospermic le- gumes and cereals than between non-endospermic and endospermic legumes. </p><p>Jerry M. Baskin, Lexington, Kentucky </p><p>M. W. Dick &amp; D. Edwards (eds), Contributions to Palaeobotany. A retirement tribute to Professor W. S. Lacey. 1983. X + 225 pp. Academic Press, Lon- don New York etc. (reprinted from Bot. J. Linn. Soc. Vol. 86). ISBN 0-12-215120-8. Price 9.60. </p><p>For the study of fossil plants to be successful, palaeobotanists must extend their interest across the continuum between biology and geology. Pro- fessor William L. Lacey of the University College of North Wales, Bangor, realized this throughout his scientific career and also the outstanding collection of papers offered to him on his retirement clearly demonstrates the interdisciplinary status of modern palaeobotany. Following an appreciation of the man and his work by F. A. Hibbert, a dozen articles cover a selection of fundamental developments in the fields of Proterozoic, Palaeozoic, Mesozoic and Caenozoic palaeobotany. The articles are written at research level but each one contains sufficient ex- planatory information to aid those who are not expert in the particular subject under investigation. </p><p>In recent years the search for Proterozoic fila- mentous and coccoid microfossils has intensified throughout the world. On the basis of an Australian assemblage M. D. Muir demonstrates the potential of these remains in environmental analysis. Com- parable algal remains, surprisingly well preserved, are described in detail by D. S. Edwards and A. G. Lyon from the Scottish Rhynie Chert, a Devonian deposit since long famous for its record of early vascular plants. Together with the Silurian, the Devonian constitutes indeed one of the most chal- lenging periods for palaeobotanical research, the time when land plants proliferated and progressed from small free-sporing homosporous plants to seed-bearing plants. Four contributions based on material from Ireland and North America offer valuable new information on Cooksonia, consid- ered to be the earliest erect fertile land plant of </p><p>possible pteridophyte affinity (D. Edwards, J. Fee- ban and D. G. Smith), on Baragwanathia (F. M. Hueber) and Haskinsia (J. D. Grierson and H. P. Banks), two genera of Devonian lycopodiophytes, as well as on Laceya(B. 1. May and L. C. Matten), a new genus of Devonian pteridosperms. In contrast to Silurian and Devonian palaeobotany, the study of Carboniferous plants is often characterized by an extreme abundance of material. Among the best- known fossil plants are certainly a number of taxa of Carboniferous arborescent lycopodiophytes. Yet, new and original contributions to our understand- ing of these plants can still be made as evidenced by the taxonomic reconsideration of Lepidostrobus (S. D. Brack-Hanes and B. A. Thomas) and the biometric approach to the problem of leaf and stem growth in the Lepidodendrales (W. G. Chaloner and B. Meyer-Berthaud). One of the most reward- ing topics of research in the Mesozoic is the study of the diversified Jurassic and Cretaceous gymno- sperms. On the basis of material from England and Africa, detailed new information became available on the pteridosperm Pachypteris (T. M. Harris) and the conifers Frenelopsis (J. Watson) and Pseu- dofrenelopsis (K. L. Alvin). To a large extent Cae- nozoic palaeobotany can make use of our knowl- edge on living floras and vegetation. Thus it is possible, even in the Tertiary, to provide realistic palaeoecological interpretations of plant-bearing sequences by means of direct references to modern environments. Such an approach is well exempli- fied by an elaborate study of palaeofloristic assemb- lages from the Oligocene of the Isle of Wight (M. E. Collinson). </p><p>H. Visscher, Utrecht </p><p>Postglacial dynamics of European vegetation </p><p>B. Huntley &amp; H. J. B. Birks. An Atlas of Past and Present Pollen Maps of Europe: 0 13 000 Years Ago. 1983. XIV +667 pp., plus 34 overlays, maps. Cambridge University Press, Cambridge. ISBN 0- 521-23735-1. Price 85.00 (US $174.00). </p><p>Pollen analysis is a source of information on the long-term dynamics of vegetation at the continental scale. Pollen data typically come from open ombro- trophic mires or from moderate-sized lakes, with </p></li><li><p>pollen 'source areas' ca 103 km 2 for most tree pollen types. During the last glacial and late glacial peri- ods (up to 10 000 years BP) much of Europe was treeless, and pollen analysis for these times yields more local, floristic information; pollen analysis also gives information on past land use by humans; pollen profiles from small basins within woodlands can record stand-scale (ca 0.1 ha) compositional changes. But perhaps most importantly, the Euro- pean pollen record for the postglacial is a record of long-term, regional changes in forest composition in response to climatic change, and the study of vegetation dynamics on this spatial and temporal scale requires a geographical perspective. </p><p>'Pollen maps' were invented by L. von Post, the Swedish pioneer of pollen analysis, in the 1920s. W. Szafer in the 1930s introduced 'isopoll maps', iso- line maps of pollen percentages, and used them to illustrate the postglacial range-boundary exten- sions of Picea and Fagus in Poland. Isopoll maps are now widely used and are (more reliably) based on the independent chronology provided by radio- carbon dating. Huntley and Birks' work represents the most ambitious attempt so far to map vegeta- tion changes through successive millennia by means of isopoll maps. This book has its faults; but it is a landmark work in the history of pollen analysis. </p><p>Huntley and Birks assembled over 400 published and unpublished pollen diagrams chosen to achieve as good geographic coverage as possible for broad- scale pollen mapping of Europe. Data were being added to the data base up to mid-1980; no new data were added thereafter. 'Europe' was taken to extend eastwards beyond 40 E, although the authors did not include all the Soviet data they might have in- cluded. The data are most sparse in some Balkan areas and the west Mediterranean area, although that is not the authors' fault. Rather surprisingly, Europe is also taken to include Greenland, al- though the data from Greenland are scarcely exten- sive enough for mapping. Isopoll maps are given for (generally) 1 000-year intervals for all of Europe's major tree genera and some shrub taxa (from Abies, Acer and AInus to UImus, Viscum and Vi- tis), plus a few major herbaceous pollen types, aquatics and pteridophytes. An introductory series of maps based on surface samples and core tops indicates the characteristics of isopoll maps as vege- tation maps. Transparent overlays show the loca- tions of sites used to generate maps for each time </p><p>117 </p><p>plane. The maps illustrate vegetation changes on a continental scale. With a mapping interval of 1000 years, species' ranges and abundance distribu- tions look impressively dynamic. The authors dis- cuss the extent to which one can interpret the maps quantitatively. Pollen percentages relate to forest composition through transformations that are be- coming increasingly well understood, although quantitative calibrations are as yet only available for a few areas. Some pollen types are biased up- wards and some downwards in abundance by dif- ferential pollen production and dispersal ability. But to a first approximation, pollen percentage maps can be interpreted as linear transformations of generalized relative abundance maps; range lim- its can usually be inferred from the locations of isolines of some limiting value, beyond which pollen occurrences represent long-distance input. </p><p>Perhaps the most striking thing about these maps is the extraordinary richness of the phenomena they record: asynchronous expansions of distributions from glacial-age refugia; periods of stasis and peri- ods of rapid migration; spatial and temporal varia- tion in rates of migration and retreat of each taxon; changes in the steepness of vegetational gradients, notably the gradual intensification of the decid- uous/ Mediterranean ecotone after 6 000 BP; the appearance of 'new' formations, such as the Hun- garian steppes after 4 000 BP, and the disappear- ance of old ones, such as the north European mixed pine-and-deciduous forests before the invasion of Picea from the east; the near-synchronous collapse of Ulrnus at 5 000 BP in northwest Europe; and much more. Confronted with this richness, the au- thors repeatedly note the difficulties associated with simplistic explanations, and stress that the complexity arises from the individualistic responses of taxa to their physical and biotic environment. Thus they naturally focus on species dynamics, rather than formation dynamics. The book's con- cluding discussion is an interesting, if sometimes contentious, treatment of species' range dynamics in relation to their glacial refugia and limiting mi- gration speeds. (Contentious because the migration rate of a taxon's boundary is only an intrinsic spe- cies property if climate is not limiting. Here the authors clearly favour the climatic disequilibrium hypothesis, which would allow species' distribu- tions to have very long historical memories.) </p><p>The main part of the book is structured taxon by </p></li><li><p>118 </p><p>taxon, with a short biographical sketch of each. These sketches summarize the natural history of each taxon. They make fascinating reading, even if some of the information is irrelevant, such as the phytosociology of Abies cephalonica communities, or the many uses of Pistacia lentiscus gum. My first real problem with the book concerns the interpreta- tions offered for various aspects of the postglacial dynamics of many of the taxa. About evergreen oaks (Quercus ilex, Q. coccifera and Q. rotundifo- lia), to take an arbitrary example: 'The subsequent slow increase of pollen values in the Mediterranean after 8 000 BP may reflect further gradual climatic change, such as increasingly xeric conditions... Alternatively the increase may reflect slow expan- sion from centres established when competition was less intense, or the slow development of second- ary xeric woodlands where man had cleared the primary, more mesic, vegetation. The decline in values subsequent to 2 000 BP might result from anthropogenic clearance, although the contempo- raneous reduction of range in France suggests that . . , climatic deterioration cannot be excluded as a possible cause' (p. 371, italics mine). Similar equivocation characterizes most of the authors' at- tempts to explain the specific phenomena that merge from mapping. I sense a paradox here. While this work clearly indicates to me the inadequacy of the traditional, often parochial 'explanations' for vegetational changes recorded within limited areas, and surely opens up the field for a more rigorous analysis, the authors nevertheless seem unwilling to accept that data are just data, and that satisfying explanations cannot arise 'inductively' from these data in the absence of a strong theoretical base - a base which the overly empiricist tradition of Euro- pean pollen analysis has conspicuously failed to produce. It is as if the authors were in despair about the complexity they have revealed, struggling to take account of diverse opinions that have been expressed in the literature, and not recognizing that their work should constitute the beginning of an exciting scientific enterprise, conducted along very different lines from those that have been the unex- am...</p></li></ul>

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