Foreword ........................................................ v
Prologue ....................................................... ix
Section I Conifer Reproductive Biology Overview
1 Introducing Conifers ......................................... 3
1.1 Gymnosperms ............................................. 4
1.2 Conifer Families: Classification and Geographic
Distribution ............................................ 4
1.3 Fossil Record for Early Seed Plants ..................... 7
1.3.1 Terrestrial Invasion of Land Plants .............. 9
1.3.2 Heterospory ...................................... 9
1.3.3 The Concept of Hydrasperman Reproduction ......... 9
1.3.4 Cordaites: Tree-Like Gymnosperms ................ 10
1.3.5 Walchian Gymnosperms as Transition Conifers ..... 10
1.3.6 Rapid Conifer Diversification in the Mesozoic
Era ............................................. 11
1.3.7 Rise and Spread of Angiosperms .................. 12
1.3.8 Modern Conifer Reproduction Evolved by
the Mesozoic Era ................................ 12
1.3.9 Distribution of Modern Conifers ................. 12
1.4 Fossil Record for the Pinaceae ......................... 13
1.5 Examples of Other Conifers as Living Fossils ........... 15
1.5.1 The Metasequoia-Dominaled Forest in Canadian
High Arctic ..................................... 15
1.5.2 Pinus krempfii in the Da Lat Plateau of
Vietnam ......................................... 16
1.6 Closing ................................................ 18
References .................................................. 19
2 The Diplohaplontic Life Cycle ............................... 23
2.1 An Overview of the Conifer Life Cycle .................. 25
2.2 Juvenility ............................................. 26
2.3 Reproductive Onset Versus Reproductive Competence ...... 26
2.4 Apical Meristem Organization for Reproductive
Initials ............................................... 27
2.5 Female and Male Strobilus Development .................. 28
2.6 Female Meiosis ......................................... 31
2.7 Monospory: From Female Megaspore to Gametophyte ........ 31
2.8 Male Meiosis, Microspores and Male Gametophytes ........ 32
2.9 Syngamy, Fertilization and Seed Maturation ............. 34
2.10 Closing ................................................ 34
References .................................................. 35
Section II Consequences of Heterospory
3 Separate Female and Male Meioses ............................ 39
3.1 Taxon-Specific Recombination Modification Systems ...... 40
3.2 Strict Diploidy in the Pinaceae Family ................. 40
3.3 Rare Polyploid Exceptions in Other Conifer Families .... 42
3.4 Conifer Have Large Stable Genomes ...................... 42
3.5 Supernumerary Chromosomes .............................. 43
3.6 Stages of Meiosis ...................................... 44
3.7 Chromosomal Segregation as a Source of Variation ....... 45
3.8 Reciprocal DNA Exchange During Prophase 1 .............. 45
3.8.1 Female Meiosis: A Case of Monospory ............. 47
3.8.2 Male Meiosis Produces Four Microspores .......... 48
3.9 From Sex-Specific Meiotic Events to Genetic Mapping .... 48
3.10 Closing ................................................ 51
References .................................................. 51
4 The Female Gametophyte Inside the Ovule ..................... 55
4.1 Female Strobilus ....................................... 56
4.2 Ovular Anatomy ......................................... 59
4.3 Female Meiosis Takes Place Inside the Nucellus ......... 60
4.4 From Megaspore and Monospory to Haploid Female
Gametophyte ............................................ 61
4.4.1 Free Nuclei Stage ............................... 62
4.4.2 Cellularization Stage ........................... 62
4.4.3 Cellular Growth Stage ........................... 63
4.5 Variations in Female Gametophyte Development ........... 63
4.6 Ploidy Levels for the Female Gametophyte in Conifers ... 64
4.7 Variants in Microspore and Pollen Morphology for
Conifers ............................................... 65
4.8 Closing ................................................ 67
References .................................................. 67
5 The Male Gametophyte Enclosed in a Pollen Wall .............. 69
5.1 Male Strobilus ......................................... 71
5.2 Sporangial Sacs Attached to Each Microsporophyll ....... 73
5.3 Microspore Polarity Determined During Male Meiosis ..... 73
5.4 Male Gametophyte Enclosed in Pollen Wall ............... 74
5.4.1 Exine Formation ................................. 74
5.4.2 Intine Formation ................................ 74
5.5 From Microspore to Male Gametophyte .................... 75
5.6 Predicting Time of Pollen Grain Release ................ 76
5.7 Quantity of Pollen Released ............................ 77
5.8 Persistent Pollen Germination Under Laboratory
Conditions ............................................. 78
5.9 Long-Distance Travel for Pine Pollen ................... 78
5.9.1 Measuring Terminal Velocity ..................... 80
5.9.2 The Open Question of Long-Distance Pollen
Germination ..................................... 84
5.10 Variants in Microspore and Pollen Morphology for
Conifers ............................................... 85
5.11 Closing ................................................ 86
References .................................................. 87
6 Pollination and Fertilization ............................... 91
6.1 Female Strobilus Receptivity ........................... 93
6.2 Pollination Drop: Localized Exudation from Each
Ovule .................................................. 95
6.3 Pollen Capture and the Role of the Micropyle ........... 95
6.4 Composition and Function of the Pollination Drop ....... 97
6.5 Pollen Germination into the Nucellus ................... 99
6.6 Pollen Tube Dormancy .................................. 100
6.7 Female Gametophyte Development After Pollination ...... 101
6.8 Fertilization ......................................... 101
6.9 Different Female Reproductive Cycles .................. 101
6.9.1 One-Year Reproductive Cycle .................... 102
6.9.2 Two-Year Reproductive Cycle .................... 102
6.9.3 Three-Year Reproductive Cycle .................. 102
6.10 Closing ............................................... 103
References ................................................. 104
7 Syngamy, Embryo Development and Seed Dispersal ............. 107
7.1 Syngamy and Organelle Sorting ......................... 108
7.1.1 Inheritance of Maternal Mitochrondria (M)
and Paternal Plastids (P) for the Pinaceae
and the Taxaceae ............................... 109
7.1.2 Inheritance of Paternal Mitochrondria (M)
and Paternal Plastids (P) for
the Cupressaceae and the Araucariaceae ......... 109
7.2 Two Types of Polyembryony ............................. 110
7.3 Four Patterns of Polyembryony ......................... 110
7.3.1 Pattern of Both Simple (S) and Cleavage (C)
Polyembrony .................................... 110
7.3.2 Pattern of Simple Polyembryony (S) ............. 111
7.3.3 Pattern of Cleavage Polyembryony (C) ........... 111
7.3.4 Pattern of No Polyembryony (NP) ................ 111
7.4 From Many to One: The Story of a Single Dominant
Embryo ................................................ 112
7.5 Stage of Embryo Development ........................... 112
7.5.1 Proembryo Formation ............................ 113
7.5.2 Early Embryogeny ............................... 114
7.5.3 Late Embryogeny ................................ 115
7.6 Seed Dispersal ........................................ 117
7.6.1 Windborne Dispersal ............................ 117
7.6.2 Bird-Mediated Dispersal ........................ 118
7.7 Closing ............................................... 119
References ................................................. 119
Section III Mating System Dynamics: Form Versus Chance
8 The Dynamic Wind-Pollinated Mating System .................. 125
8.1 Wind-Pollinated Mating System: Outcrossing or Mixed
Selfing/Outcrossing ................................... 126
8.2 Selfing ............................................... 127
8.2.1 Selfing Avoidance .............................. 128
8.2.2 Selfed Embryo Deaths During Development ........ 128
8.3 Interspecific Hybridization ........................... 128
8.4 Reproductive Sterility ................................ 132
8.5 Closing ............................................... 133
References ................................................. 133
9 The Embryo Lethal System ................................... 137
9.1 Moderate Selfing Rates yet Low Selfed Seed Recovery ... 138
9.2 Simple Polyembryony is not a Barrier Against Selfs .... 139
9.3 Measures of Selfed Embryo Death ....................... 141
9.3.1 Lethal Equivalents ............................. 141
9.3.2 Lethal Numbers ................................. 143
9.4 The Embryo Lethal System .............................. 143
9.5 Deleterious Alleles for Embryo Viability Loci Versus
an Embryo Lethal System ............................... 144
9.6 Exploring Phylogenetic Limits to the Embryo Lethal
System ................................................ 145
9.7 Studying Selfed Embryo Death using Molecular
Dissection ............................................ 146
9.7.1 Sources of Bias for Molecular Dissection ....... 147
9.7.2 Bias from Gametic or Gametophytic Selection .... 147
9.7.3 Marker Systems and Map Density Impose
Experimental Design Limitations ................ 147
9.8 Genomic Architecture for Zygotic Lethal Factors ....... 149
9.9 Closing ............................................... 150
References .................................................... 150
Conclusion .................................................... 155
Glossary ...................................................... 161
Index ......................................................... 167
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