Faculty of Science, School of Sciences, Natabua Campus Lautoka BIO706 Embryology Lectures 21:Flowering Plant Reproduction - I

QUESTIONS WE TRY TO ANSWER: How does a single cell become a complex organism? What mechanisms / factors control development? Cell fate in order to produce a functional plant? Plant development

Angiosperm development alternation of generations diploid phase = sporophyte embryogenesis, germination, primary and secondary development vegetative & reproductive development juvenile & adult phase, a phase change haploid phase = gametophyte megaspore  female gametophyte microspore  male gametophyte

Gametophyte development female gametophyte = embryo sac -carpels: ovary, style & stigma -ovules: nucellus, integuments, micropyle male gametophyte -microspore mother cells surrounded by tapetum  meiosis  microspores  pollen grains

Sexual life cycle of an angiosperm

Flower and its parts

Meiosis occurs in sporangia of sporophytes Angiosperms Key Haploid Diploid Microsporangium Microspore Alternation of Generations Meiosis Sporophyte Meiosis Meiosis occurs in sporangia of sporophytes Megasporangium Gametophytes Megaspore Fertilization

Spores divide by mitosis and develop into mature gametophytes Angiosperms Key Haploid Diploid Microsporangium Microspore Alternation of Generations Meiosis Pollen Sporophyte Spores divide by mitosis and develop into mature gametophytes Meiosis Megasporangium Gametophytes Megaspore Embryo sac Fertilization

Alternation of Generations Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Pollen Sporophyte Specialized gametophyte cells divide by mitosis to form gametes Meiosis Megasporangium Gametophytes Megaspore Embryo sac Egg 2 sperm Fertilization

Alternation of Generations Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Pollen Sporophyte Seedling Meiosis Megasporangium Gametes fuse during fertilization to produce a zygote Gametophytes Megaspore Embryo Embryo sac Egg Zygote 2 sperm Endosperm Fertilization

A sporophytes’ male reproductive structures: Stamen Anther Filament

A sporophytes’ male reproductive structures: Each anther contains multiple pollen sacs (microsporangia)

A sporophytes’ male reproductive structures: Each pollen sac contains mutiple diploid microsporocytes (microspore mother cells)

A sporophytes’ male reproductive structures: Each microsporocyte divides by meiosis to produce 4 haploid microspores

A sporophytes’ male reproductive structures: Each microspore divides once by mitosis to form an immature male gametophyte (pollen grain) A single tube cell encloses a single generative cell

reproductive structures: A sporophytes’ male reproductive structures: The pollen grain matures into an adult male gametophyte when its generative cell divides by mitosis to produce two sperm The adult male gameto-phyte is a fully mature, indepen-dent plant with only 3 cells

A sporophytes’ female reproductive structures: Carpel Stigma Style Ovary Ovule Receptacle

A sporophytes’ female reproductive structures: Each ovule contains a megasporangium Each megasporangium contains a megasporocyte (megaspore mother cell)

A sporophytes’ female reproductive structures: A megasporocyte divides by meiosis to form 4 cells Only 1 of the 4 cells survives: the megaspore

A sporophytes’ female reproductive structures: The megaspore’s nucleus divides 3 times: giving 1248 nuclei Membranes then partition the 8-nucleate immature gametophyte cell into 7 smaller cells (one with 2 nuclei)

A sporophytes’ female reproductive structures: The 7 cells: 1 egg 1 cell with 2 polar nuclei 5 other cells The 7 cells comprise the mature, completely dependent female gametophyte (embryo sac)

A pollen grain disperses to a stigma Double fertilization of angiosperms (and independently derived in a few gymnosperms) A pollen grain disperses to a stigma (pollination) The tube cell grows into a pollen tube

The 2 sperm cells travel down the pollen tube to the embryo sac Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac

The 2 sperm cells travel down the pollen tube to the embryo sac Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac

The 2 sperm cells travel down the pollen tube to the embryo sac Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac

1 sperm fuses with the egg (fertilization) Double fertilization of angiosperms (and independently derived in a few gymnosperms) 1 sperm fuses with the egg (fertilization) 1 sperm fuses with the polar nuclei to form the first cell of the endosperm (triploid)

Structural barriers to pollination, e.g., pin vs. thrum flowers bisexual flowers Structural barriers to pollination, e.g., pin vs. thrum flowers

Genetic self-incompatibility, gauged by S-genes Other mechanisms used by bisexual flowers to avoid self-fertilization: Genetic self-incompatibility, gauged by S-genes

Other mechanisms used by bisexual flowers to avoid self-fertilization: Genetic self-incompatibility, gauged by S-genes

Other mechanisms used by bisexual flowers to avoid self-fertilization: Genetic self-incompatibility, gauged by S-genes

Development of the seed and fruit The first mitotic division of the zygote is asymmetric This asymmetry provides the first environmental difference experienced by the differentiating cells and establishes the root-shoot axis Ovary Receptacle

Development of the seed and fruit The sporophyte embryo develops from the zygote The endosperm develops from the triploid endosperm nucleus Ovary Receptacle

Development of the seed and fruit The ovule integuments become the seed coat Tissues of the ovary (and sometimes the receptacle) become the fruit Ovary Receptacle

Development of the seed and fruit The ovule integuments become the seed coat Tissues of the ovary (and sometimes the receptacle) become the fruit

Development of the seed and fruit There are many kinds of fruits Carpels Flower Stigma Stamen Ovule Carpel (fruitlet) Each segment develops from the carpel of one flower Stigma Seed Stamen Pea Raspberry Pineapple Simple fruit - single carpel of one flower Aggregate fruit - many separate carpels of one flower Multiple fruit - many carpels of many flowers

Development of the seed and fruit Eudicot embryos develop two cotyledons

Development of the seed and fruit Eudicot embryos develop two cotyledons Monocot embryos develop a single cotyledon

Development of the seed and fruit Cotyledons may absorb endosperm throughout their functional lives (e.g., castor bean) Cotyledons may alternatively function as storage organs that absorb the endosperm prior to a seed’s germination (e.g., common bean)

Development of the seed and fruit The radicle is the first structure out of the seed coat In some eudicots the hypocotyl (embryonic axis below cotyledons) pushes up through the soil

Development of the seed and fruit The radicle is the first structure out of the seed coat In some eudicots the epicotyl (embryonic axis above cotyledons) pushes up through the soil

Development of the seed and fruit In many monocots, the cotyledon remains in the seed coat, and the coleoptile pushes up through the soil

Gymnosperms rely on wind to move pollen from male to female cones The ovule exudes sap to trap pollen

Around 150 m.y.a. some insects fed on both protein-rich pollen of male cones and sugar-rich secretions of female cones… This may have led evolutionarily to the origin of Angiosperms and animal-mediated pollination

Angiosperms have formed many partnerships with animals to move their pollen

Questions are welcome