THE

EMBRYOLOGYOF

ANGIOSPERMS

IMAGE ON THE COVER

In vitro Torenia fournieriMost of the pollen tubes emerging from the cut end

of the style are growing towards the ovules.

Courtesy

S S BhojwaniEmeritus Professor of Botany (Retd)

Dayalbagh Educational InstituteDayalbagh, Agra

S P BhatnagarProfessor of Botany (Retd)University of Delhi, Delhi

P K DantuDepartment of Botany

Dayalbagh Educational InstituteDayalbagh, Agra

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THEEMBRYOLOGY

OFANGIOSPERMS

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VIKAS®

The Embryology of AngiospermsISBN: 978-93259-8129-4

First Published 1974Sixth Edition 2015

Vikas® is the registered trademark of Vikas Publishing House Pvt LtdCopyright © Authors, 1974, 1999, 2008, 2015

Since the last revision of this little book rapid advances have been made inthe field of embryology. In the post genomic era the methods used to studyplant embryology have radically changed, and powerful modern arsenalof biological techniques are being applied to understand the developmentalaspects and genetic and molecular bases of embryological processes.Embryological systems, such as tip-focused growth of pollen tube cell anddifferentiation of entire plantlets from a single celled zygote through welldefined stages are also attracting the attention of plant physiologists,molecular biologists and geneticists. It has become possible to generate tissuespecific mutants by T-DNA insertional mutagenesis, use of green fluorescentprotein probes for live imaging of growing cells and tissues and to analyzegene expression in few celled structures, such as early stages of embryo,and constituent cells of the male and female gametophytes. These techniques,combined with the development of high resolution confocal laser scanningmicroscopy, have provided non-invasive methods to view live processes,such as pollen tube growth in the pistil and double fertilization under insitu conditions. For such studies Arabidopsis thaliana, with short life cycleand small genome, has emerged as a model system. Torenia fournierii, withnaked embryo sac, has also been used to investigate the process of doublefertilization more precisely. All these developments have led to accumulationof considerable new information during the past two decades, and bookson individual topics of embryology, such as Endosperm Development (Olsen2007) and Plant Embryogenesis (Suárez and Bozhkov, 2008), have beenpublished.

The rapid and impressive advances in our knowledge of embryologicalsystems and processes inspired the revision of this book. The chapter onFertilization has been almost rewritten and considerable new informationhas been added to the chapters on embryo, sexual incompatibility andendosperm. Topics on experimental embryology have been covered inChapters 4 (genetic engineering of male sterility), 10 (In vitro Pollinationand Fertilization; Hybrid Embryo Culture), 11 (Endosperm Culture), 12

PREFACE TO THESIXTH EDITION

vi The Embryology of Angiosperms

(Embryo Culture), 13 (Somatic Embryogenesis), besides the Chapter 17. Weare confident that the students and teachers would continue to find thisupdated version more interesting and useful.

Authors

25th August 2014

During the last two decades the plant embryologists have utilized manytechniques of physics and chemistry such as electron microscopy,autoradiography, histochemistry, and chromatography, and have elucidatedseveral significant details about the structure and function of reproductiveorgans associated with seed development. Formation of pollen wall,differentiation of vegetative cell and generative cell in pollen, structure andfunction of the various components of embryo sac, pollen germination, pollentube growth, mechanism of fertilization, and early embryogeny are theprincipal areas in which substantial amount of new information has beenobtained. The science of embryology has no longer remained a purelyobservational discipline. During the last twenty years it has made notableheadway in experimentation. Some techniques of experimental embryology,such as production of haploids through anther culture, embryo culture,and controlled pollination and fertilization have proved to be of greatsignificance in genetics and plant breeding.

The absence of a comprehensive book on Angiosperm Embryology inEnglish, dealing with the recent advances in the field, has prompted us toundertake the task of preparing this book. Needless to say that whilepresenting the modern concepts and scope of the subject every care hasbeen taken not to neglect the fundamentals which are so important as abasis in any modern discipline of biology.

This book is primarily intended for B.Sc. (General and Honours) coursesof Indian universities. However, in the absence of any other comprehensivebook which includes both the classical data and the recent advances inAngiosperm Embryology, we hope that the postgraduate students wouldalso find it a useful reference book. The suggested readings at the end ofeach chapter may help the teachers as well. Despite our sincere efforts it ispossible that some important references might have escaped our attention.Also, students and teachers might feel the need for further details on certaintopics. We shall be obliged if the readers would send us their valuable

PREFACE TO THEFIRST EDITION

viii The Embryology of Angiosperms

suggestions in this regard or on any other aspect of the book. These wouldhelp us in the next edition.

We are deeply indebted to our teacher Professor B.M. Johri who trainedus in plant embryology. The help of Dr. V.S. Jaiswal in various ways isgratefully acknowledged. Most of the illustrations used in this book havebeen drawn from the works of other authors to whom we are extremelygrateful. We express our warm appreciation to our wives—Shaku andAsha—for their encouragement and patience during the course of thewriting of this book.

Authors

Preface to the Sixth Edition vPreface to the First Edition vii

1. HISTORICAL ACCOUNT .................................................. 1Suggested Reading 7

2. FLOWER ................................................................................... 9Calyx 12Corolla 12Androecium 13Gynoecium13Suggested Reading 13

3. MICROSPORANGIUM ...................................................... 14Anther Wall 16Epidermis 16Sporogenous Tissue 26Rare Features 31Suggested Reading 31

4. MALE GAMETOPHYTE—DEVELOPMENT ............... 33Formation of Vegetative and Generative Cells 33Inheritance of Cytoplasmic Traits 46Pollen Wall 48Abnormal Features 53Genetic Engineering for Fertility Control 56Suggested Reading 57

CONTENTS

5. MALE GAMETOPHYTE—MORPHOLOGY ................ 58Pollen Wall Features 60Scope of Palynology 62Preparation of Pollen Grains 63Suggested Reading 64

6. MEGASPORANGIUM ........................................................ 65Types of Ovules 65Integuments 67Nucellus 72Megasporogenesis 75Special Features 80Suggested Reading 83

7. FEMALE GAMETOPHYTE ............................................... 85Types of Embryo Sacs 87Mature Embryo Sac 93Haustorial Behaviour of Embryo Sac 103Nutrition of Embryo Sac 105Suggested Reading 107

8. POLLINATION ................................................................... 109Anther Dehiscence 109Pollen Transfer 113Artificial Pollination 124Suggested Reading 128

9. FERTILIZATION ................................................................ 129Pollen Germination and Pollen Tube Growth 136Unusual Features 158Suggested Reading 159

10. SEXUAL INCOMPATIBILITY ....................................... 160Self-incompatibility 160Genetic Basis of Self-incompatibility 161Barriers to Fertilization 164Physiology and Biochemistry of Incompatibility 165Molecular Mechanisms of Self-incompatibility 173Biological Significance of Incompatibility 176Methods to Overcome Incompatibility 176Suggested Reading 190

x Contents

11. ENDOSPERM ...................................................................... 192Development of Endosperm 193Ruminate Endosperm 210Cytology of Endosperm 211Reserve Food Substances 213Improvement of the Nutritive Value of

Endosperm by Genetic Engineering 214Functions of Endosperm 214Morphogenetic Studies 215Suggested Reading 220

12. EMBRYO .............................................................................. 222Zygote 223Embryogeny 223Proembryo 224Suspensor 232Unusual Features 238Physiological and Genetic Control of Embryogenesis 241Nutrition of Embryo 247Suggested Reading 253

13. POLYEMBRYONY ............................................................. 255Causes of Polyembryony 262Experimental Induction of Polyembryony 263Classification of Polyembryony 270Practical Value of Polyembryony 270Suggested Reading 272

14. APOMIXIS ........................................................................... 274Vegetative Reproduction 276Agamospermy 277Genetics of Apomixis 282Techniques to Screen Apomicts 284Practical Importance 285Suggested Reading 285

15. SEED ...................................................................................... 287Seed Development 289Classification of Seeds 300Importance of Seeds 301

Contents xi

Seed Dispersal 301Seed Dormancy 308Suggested Reading 309

16. EMBRYOLOGY IN RELATIONTO TAXONOMY ............................................................... 310

Embryological Characters which have Proved ofSpecial Importance in Taxonomic Considerations 311Some Families Especially Marked Out by Their

Embryological Features 312Some Examples of The Value of Embryology inTaxonomy 314Palynology in Taxonomy 322Suggested Reading 323

17. EXPERIMENTAL AND APPLIEDEMBRYOLOGY .................................................................. 325Tissue Culture Techniques 326Haploid Production 328Androgenesis 329Gynogenesis 338Haploid Production Through Distant Hybridization 340Embryo Culture 343Nucellus Culture 348Ovule and Seed Culture 350Effect of Young Seeds on Fruit Growth 356Parthenocarpy 357Genetic Transformation 360Suggested Reading 363

Index 365

xii Contents

Historical Account 1

HISTORICAL ACCOUNT

Four thousand years ago, the Arabs had some knowledge of the part playedby pollen in fruit development in date palm. However, sexual cells wereobserved only after the invention of microscope, and the credit for this goesto Leeuwenhoek (1677). Grew (1682), for the first time, highlighted the factthat stamens are the male organs of a flower, and the pollen grains in someway influenced the ovary to produce fruit.

Camerarius (1694) had a more scientific approach. He noticed that afemale mulberry tree, near which no male plant was growing, formed onlyabortive seeds. Inspired by this discovery, he experimented with some femaleplants of Mercurialis annua. These he kept isolated from the male plants.Again, fertile seeds were not formed. He made similar observations in Ricinusand Zea mays. From these findings he concluded that anthers are the malesex organs of the plant, and the ovary, with style and stigma, the female sexorgan.

The significance of pollination in seed-set, and the importance of insectsin pollination was recognized by Kolreuter (1761). He also made notablecontribution to pollen morphology. With a primitive type of microscope, hewas able to identify two distinct layers in the covering of pollen grains.However, the most significant contribution of Kolreuter concerning sexualreproduction was the artificial production ofhybrids in plants such as Dianthus, Hyoscyamus,Mathiola and Nicotiana. He observed that if thestigma was pollinated with the pollen of the samespecies, as well as foreign pollen at the same time,normally, only the pollen of the same species wereeffective in fertilization.

As happens with many importantdiscoveries, the discovery of pollen tube was alsoan accident which triggered a chain of manysignificant events. The real credit for revealingthe actual role of pollen in fertilization goes toG.B. Amici (1824), an Italian mathematician,astronomer, and a meticulous microscope maker.

Fig. 1.1Giovanni Battista Amici

1CHAPTER

2 The Embryology of Angiosperms

While examining the stigma of Portulaca oleracea, he saw a pollen grainadhering to a stigmatic hair. He kept it under observation and, to his surprise,the pollen grain split open followed by emergence of a tube, or ‘gut’, whichentered the tissues of the stigma. Repeating his observation in 1830, Amiciconfirmed that the pollen tube, after emerging from the pollen grain, grewbit by bit and, finally, came in contact with the ovule.

Several other persons got interested in this problem, and mention maybe made of Schleiden (who with Schwann propounded the Cell Theory in1839), who made detailed observation on the ovule. He agreed with Amicias far as the growth of the pollen tube through the stigma and style and itsentry into the ovule are concerned. A man of great imagination, Schleidenasserted that the tip of the pollen tube after entering the embryo sac developedinto the embryo. According to him, the embryo sac acted only as an ‘incubator’wherein the tip of the pollen tube was nourished giving rise to a new plantlet.Such a conclusion would obviously negate sexuality in plants. Nevertheless,Schleiden was able to muster enough support for his absurd idea; notableamong his supporters was Schacht.

Amici (1842) opposed the observations of Schleiden and tried to showthat the embryo developed from a portion already existing in the ovule, andnot from the tip of the pollen tube. Schleiden (1845) ridiculed those whoraised objections against his findings, and vehemently challenged theobservations of Amici. Schleiden went to the extent of inviting people tocome and see for themselves that what he believed was the real truth.

Amici, in the face of mounting criticism, provided conclusive evidenceand demonstrated that in Orchis the ‘germinal vesicle’, which was alreadypresent inside the ovule, was stimulated by the presence of the pollen tubeand developed into the embryo (Amici, 1847). Eventually, however, it wastruth that triumphed. Amici received a lot of support from many workers,prominent among them was W. Hofmeister. In a most convincingdemonstration, Hofmeister (1849) tracedthe formation of embryo from the egg rightup to its maturity in the seed. Heconfirmed this in several genera ofangiosperms, leaving no doubt as to thecorrectness of Amici’s findings.

Schleiden and Schacht continued tohold their views for some time. It was onlywhen the evidence against their viewsbegan to grow that both of them withdrewtheir assertions. The controversy came toan end with the publication of Radlkofer(1856) in which he fully supported thedetailed observations of Hofmeister (1849)that the embryo originated from a cell ofthe embryo sac and not from the pollentube. Fig. 1.2 Wilhelm Hofmeister

The Embryology Of Angiosperms

Publisher : SChand Publications ISBN : 9789325981294Author : S. S Bhojwani, S.P. Bhatnagar, P. K. Dantu

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