Angiosperm Reproduction: Pollination, Fertilization, Embryo Development, and Apomixis

Vocabulary practice flashcards covering angiosperm reproductive biology: pollination modes and contrivances, pollen-pistil interaction, double fertilization, endosperm and embryo development, seed anatomy, and asexual reproduction pathways (apomixis, parthenocarpy, polyembryony).

Pollination

The transfer of pollen grains from the anther to the stigma of a flower, serving as an essential prerequisite for fertilization in angiosperms.

Autogamy

A type of self-pollination in which a bisexual flower is pollinated by its own pollen grains, producing offspring that are genetically identical to the parents (e.g., pea, Clitoria).

Chasmogamous Flower

A flower that opens at maturity to expose its sexual organs to external pollinating agents.

Homogamy

A contrivance favoring self-pollination where the anther and stigma of a flower mature at the exact same time.

Cleistogamy

A condition in which flowers remain closed and self-pollinate before opening, including underground flowers that never open (e.g., Commelina benghalensis).

Geitonogamy

The transfer of pollen grains from an anther to the stigma of a different flower produced on the same plant; functionally cross-pollination involving agents, but ecologically and genetically equivalent to autogamy (e.g., Cucurbita maxima).

Xenogamy

A type of cross-pollination (outbreeding) where pollen grains from one flower are deposited on the stigma of a flower of a different plant belonging to the same species, generating genetically varied offspring.

Anemophily

Pollination mediated by wind, characterized by small, inconspicuous, colourless flowers without nectar or scent, light and dry pollen produced in large numbers, and feathery stigmas (e.g., wheat, rice, corn, palms).

Hydrophily

Pollination mediated by water, occurring in approximately 30 genera of aquatic monocots (e.g., Vallisneria, Zostera, Ceratophyllum), characterized by unwettable perianth and mucilage-coated pollen.

Hypohydrophily

A form of hydrophily occurring below the water surface where pollen grains are heavier than water, sink down, and lack an exine (e.g., Zostera / sea grass).

Epihydrophily

A form of hydrophily occurring on the water surface where pollen grains float due to having a specific gravity equal to that of water, reaching floating or temporarily surface-reaching female flowers (e.g., Vallisneria).

Entomophily

Pollination mediated by insects, characterized by large, showy, brightly colored flowers with sweet odor, nectar glands, and spiny pollen (e.g., Rose, Jasmine, Cestrum).

Pollen-kit

A yellow, sticky substance surrounding the spiny pollen grains of entomophilous flowers that aids in adhesion to visiting insects.

Lever Mechanism (Turn-pipe Mechanism)

A specialized floral adaptation found in Salvia that facilitates cross-pollination by bending stamens onto the body of visiting insect pollinators.

Ornithophily

Pollination mediated by birds with small bodies and long beaks (e.g., sunbirds and hummingbirds); flowers are large, brightly colored, lacking scent, and produce profuse, dilute nectar (e.g., Bombax, Callistemon, Butea).

Chiropterophily

Pollination mediated by bats over long distances; flowers are typically dull-colored with strong fragrance, abundant nectar, and large quantities of edible pollen (e.g., Anthocephalus, Adansonia, Kigelia).

Inbreeding Depression

The reduction in biological fitness and vigor resulting from continuous self-pollination, which plants prevent using various outbreeding contrivances.

Dichogamy

An outbreeding device where anthers and stigmas mature at different times in a bisexual flower to prevent self-pollination.

Protandry

A form of dichogamy in which the androecium matures earlier than the gynoecium (e.g., in the disc florets of sunflower).

Protogyny

A form of dichogamy in which the gynoecium matures earlier than the androecium (e.g., Gloriosa).

Prepotency

The phenomenon where pollen grains from another flower germinate more rapidly on the stigma than pollen grains from the same flower (e.g., Apple).

Heterostyly (Heteromorphy)

A floral condition where stigmas and anthers are positioned at different vertical levels within flowers of the same species to physically prevent self-pollination (e.g., Primula).

Herkogamy

A mechanical barrier preventing self-pollination in a bisexual flower due to a physical separation between male and female sex organs (e.g., Calotropis, where a pentangular stigma lies above pollinia).

Self-Incompatibility (Self-Sterility)

A genetic mechanism in which the germination of pollen grains on the stigma of the same flower is inhibited by specific incompatibility proteins (e.g., Tobacco, Thea).

Pollen-Pistil Interaction

All sequential physiological and recognition events beginning from the deposition of pollen grains on the stigma up to the entry of the pollen tube into the ovule synergid.

Porogamy

The most common mode of pollen tube entry into the ovule, where it penetrates through the micropyle.

Chalazogamy

The entry of the pollen tube into the ovule through the chalazal end rather than the micropyle.

Mesogamy

The entry of the pollen tube into the ovule by piercing directly through the integuments.

Siphonogamy

The process in which non-motile male gametes are conveyed to the female gametophyte via a hollow pollen tube.

Double Fertilization

A unique angiosperm fertilization process discovered by Nawaschin in Lilium and Fritillaria, involving both syngamy and triple fusion.

Syngamy

Generative fertilization involving the fusion of a haploid male gamete with a haploid female gamete (egg cell) to produce a diploid zygote ($2n$).

Triple Fusion

Vegetative fertilization involving the fusion of a second haploid male gamete with a diploid secondary nucleus to produce a triploid primary endosperm nucleus (PEN, $3n$).

Nuclear Type Endosperm

The most common endosperm development type (found in 161 angiospermic families) where the primary endosperm nucleus undergoes repeated mitotic divisions without wall formation, creating free nuclei pushed peripherally by a central vacuole.

Cellular Type Endosperm

A type of endosperm development observed in 72 dicot families (e.g., Balsam, Petunia, Adoxa) where nuclear divisions of the primary endosperm nucleus are immediately accompanied by cell wall formation from the beginning.

Helobial Type Endosperm

An intermediate form of endosperm development occurring in the order Helobiales (e.g., Asphodelus), where the first division is followed by a transverse wall forming unequal micropylar and chalazal chambers, followed by free nuclear division.

Mosaic Endosperm

An endosperm tissue displaying patches of two distinct colors forming a mosaic pattern, as observed in corn plants.

Embryogenesis

The biological process of development of a zygote into an organized multicellular embryo at the micropylar end of the embryo sac.

Suspensor Haustorium

The swollen first cell of the suspensor located toward the micropylar end that functions to absorb nutrients for the developing embryo.

Hypophysis

The lowermost cell of the filamentous suspensor that, through further division, gives rise to part of the embryonic radicle and root cap.

Scutellum

The single, shield-shaped, terminally located cotyledon characteristic of monocot (grass) embryos.

Coleoptile

The protective sheath enclosing and shielding the embryonic plumule in monocot seeds.

Coleorhiza

The protective sheath enclosing and shielding the embryonic radicle and root cap in monocot seeds.

Perisperm

A persistent, thin, papery nutritive layer of the nucellus that remains outside the embryo sac in certain mature seeds (e.g., black pepper and beet).

Albuminous (Endospermic) Seeds

Seeds in which the endosperm is only partially consumed during embryo development and remains conspicuous to store food reserves (e.g., Castor, Coconut, Maize).

Ex-albuminous (Non-Endospermic) Seeds

Seeds in which the endosperm is completely absorbed and disorganized during development, storing reserves primarily in large cotyledons (e.g., Pea, Bean).

Seed Dormancy

A temporary state of metabolic arrest and physiological adaptation that inhibits mature, viable seeds from germinating even in the presence of favorable environmental conditions.

Apomixis

The formation of an embryo and seed via asexual reproduction without the involvement of gamete formation, meiosis, or syngamy.

Apogamy

The development of an embryo or embryo-like structure directly from a gametophytic cell (egg cell or male gamete) without fertilization.

Apospory

The formation of an apomictic embryo sac or diploid gametophyte directly from vegetative cells of the sporophyte (such as nucellar cells) without meiosis (e.g., Orange, Mango).

Diplospory

A form of recurrent apomixis in which an unreduced embryo sac is derived directly from a diploid megaspore mother cell (e.g., Taraxacum).

Parthenocarpy

A phenomenon coined by Noll (1902) wherein fruit develops without fertilization, resulting in seedless fruits (e.g., Pineapple, Banana, Papaya) naturally induced by auxin IAA.

Polyembryony

The development of more than one embryo inside a single seed, first discovered by Antonie van Leeuwenhoek (1719) in the genus Citrus.

Adventive Polyembryony

A condition where additional embryos develop directly from diploid maternal sporophytic cells, such as the nucellus or integuments, alongside the zygotic embryo (e.g., Citrus, Mango).

Cleavage Polyembryony

The formation of multiple embryos resulting from the division or cleaving of a single zygotic proembryo into multiple independent developmental units.

Agamospermy

The phenomenon wherein plants produce viable seeds containing an embryo formed completely without meiosis and syngamy.