Plant Reproduction, Botany - PDF Document

REPRODUCTION, GROWTH AND DEVELOPMENT IN PLANT DR MAHASSAN MAMAT PASUM  REPRODUCTION IN PLANT Sexual, asexual and vegetative reproduction in flowering plants; parthenogenesis  OBJECTIVES 1. To explain asexual and...

REPRODUCTION, GROWTH AND DEVELOPMENT IN PLANT DR MAHASSAN MAMAT PASUM  REPRODUCTION IN PLANT Sexual, asexual and vegetative reproduction in flowering plants; parthenogenesis  OBJECTIVES 1. To explain asexual and sexual reproduction in angiosperms. 2. To explain parthenogenesis. 3. To explain how the following structures may be used to propagate plants asexually: rhizomes, tubers, stolons, corms and bulbs. 4. To explain the development of pollen grains. 5. To explain the development of the embryo sac and ovum.  INTRODUCTION o Angiosperms / flowering plants include at least 300,000 species. o The largest, most successful group of plants - can reproduce both sexually and asexually. o Two types of plants reproduction: 1) Asexual reproduction - vegetative growth; parthenogenesis; tissue culture propagation. 2) Sexual reproduction. ASEXUAL REPRODUCTION IN FLOWERING PLANTS o Doesn’t usually involve the formation of flowers, seeds and fruits. o A single parent organism produces offspring which are genetically identical (unless mutation occurs) to each other and to the parent. o Without genetic recombination. o Proceeds by way of mitosis. o Many methods – most of which involve modified vegetative organs – stems (rhizomes, tubers, bulbs, corms and stolon), roots and leaves. There are 3 types of asexual reproduction in flowering plants. 1. Occurs when new individuals are formed from tissues which are not normally involved in sexual reproduction. This is called vegetative propagation. 2. Embryos are formed without prior fertilization, that is by parthenogenesis. crucial - 3. Artificial propagation.  I) Vegetative propagation 1. A new plant develops from tissues or structure that drops from the parent plant or is separated from it which are not normally involved in sexual reproduction 2. root, stem, leaf - give rise to new differentiated tissues, and later separate to become a new individual. 3. Jade plant, African violet MECHANISMS EXAMPLES CHARACTERISTICS knowledge TABLE 1: Vegetative reproduction on modified stems FIGURE 1: Methods of vegetative propagation Rhizome – horizontal underground stems – irises, bamboos, ginger, grasses A corm is an underground stem that is almost entirely stem tissue surrounded by a few papery scales – crocus, gladiolus, cyclamen Potato plants form rhizomes, which enlarge into tubers at the ends. A bulb is a short underground stem to which overlapping, fleshy leaves are attached; most of the bulb consists of leaves – lilies, tulips, onions.  ⑳ Strawberries reproduce asexually by forming stolons  II) Artificial propagation 1. A new plant develops from cuttings or fragments of shoot systems - African violets and jade plants can be propagated from leaf cuttings. 2. Tissue culture propagation - A new plant in induced to arise from a parent plant cell. o Tiny plant bits are grown in rotating flasks containing a liquid growth medium. o Orchid; lily; wheat; rice; corn; tulip.  III) Parthenogenesis A crucial A reproductive strategy that involves development of a female (rarely a male) gamete (sex cell) without fertilization. It naturally occurs in a variety of plant and animal species. It occurs commonly among lower plants and invertebrate animals and rarely among higher vertebrates.  Parthenogenesis in plants The development of new individuals from an unfertilized haploid egg / by developing adventitiously, from tissue surrounding the embryo sac. Usually is found in combination with apomeiosis (the omission of meiosis) and pseudogamous or autonomous (with or without central cell fertilization) endosperm formation, together known as apomixis (clonal seed production).  A familiar example is the reproduction of viable seeds with asexual embryos identical to the parent. An embryo develops without nuclear / cellular fusion. Occurs when embryos and seeds are formed without meiosis / fertilization taking place. E.g. citrus fruits – orange; grapefruits; rose; tangerines and in their hybrids. E ⑧  Parthenocarpy and Parthenogenesis Parthenocarpy - development of fruit takes place without fertilization, whereas parthenogenesis development of a new organism takes place without fertilization of an ovum. Parthenocarpy seedless fruits are produced, whereas in parthenogenesis female clones are produced and cannot reproduce sexually.  Parthenogenesis and apomixis Parthenogenesis is a type of apomixis where the egg cells help in the development of an embryo. It produces a genetically identical clone of the mother cell. Here, the embryos develop from an unfertilised egg, and the offspring are genetically identical. The apomictic parthenogenesis produces the clone of the mother.  Parthenogenesis in animals Parthenogenesis is reproduction without fertilization, an ovum developing into a new individual without fertilization by a sperm. In vertebrates, parthenogenetic “species” are the result of modification of ovum development, usually changes in meiosis, leading to eggs produced with multiple sets of chromosomes. rotifers, aphids, ants, wasps, and bees. SEXUAL REPRODUCTION IN FLOWERING PLANTS 1. The premier reproductive mode of flowering plant life cycles. 2. Involves the formation of spores and gametes, both of which develop inside the specialized reproductive shoots called flowers. 3. Includes meiosis and the fusion of reproductives cells – egg and sperms cells – gametes. 4. The union of gametes called fertilization – occurs within the flower’s ovary. 5. Haploids gametes fuse to form a diploid zygote which develops via an embryo into a new plant.  Kinds of Flowers Perfect flowers – Have both male and female parts Imperfect flowers – Are either male or female – Same plant may have both male and female flowers – Sexes may be on separate plants Flowers are very important for identification of the plants. A typical dicotyledonous flower consists of s four main whorls. mustknow a) Calyx (whorl of sepals) b) Corolla (whorl of petals) c) Androecium (whorl of stamens) d) Gynoecium (whorl of carpels).  STAMEN CARPEL (male reproductive part) (female reproductive part) filament anther stigma style ovary Nonfertile parts – Sepals – Receptacle Fertile parts – Male stamens – Female carpels OVULE (ovary) petal (all petals (forms combined are the within flower’s corolla) ovary) sepal (all sepals combined are the flower’s calyx) receptacle FIGURE 2: Flower structure * Common terms used in describing a flower A a) Receptacle - the base of a flower for attachment of other parts of a flower b) Calyx - the outermost whorl; it comprises individual units called sepal. The sepals are mostly green and leaf-like. Calyx protects the flower at the bud stage. c) Corolla - This is the second whorl from the edge of the flower. Each individual unit is called a petal. In dicotyledons, the petals are brightly colored. d) Perianth - When the sepals and petals cannot be differentiated, the outer two whorls are referred to as the perianth. In this case, the flower does not have a distinct calyx or corolla. e) Androecium - the male part of the flower consisting of stamens f) Gynoecium - the female part of the flower consisting of carpels  Gynoecium (pistil) 1. The female part of a flower and is centrally located. 2. Consists of one or more carpels which may be free or fused. Each carpel consists of a cavity containing one or more ovules. 3. Ovary - the cavity with the ovules. 4. Stigma - at the free end of the carpel is a sticky surface. 5. Style - the structure that connects the stigma and ovary. 6. The ovule contains the female gamete in the embryo-sac. The embryo-sac represents the female gametophyte in the life cycle. 7. After fertilisation, the ovule develops to form the seed and the ovary develops to form the fruit. FLORAL FORMULA (1)  FLORAL FORMULA (2) A(α) FLORAL FORMULA (3) FLORAL FORMULA (4) Flame of the forest (a) Classification Dendrobium a) Classification Kingdom : Plantae Division : Angiospermophyta Class : Monocotyledoneae Order : Orchidales Family : Orchidaceae Genus : Dendrobium b) Taxonomic features : herbaceous; epiphyte; alternate leaves  Pollen Formation 1. Each anther has four pollen sacs 2. Inside the pollen sacs, cells undergo meiosis and cytoplasmic division to form haploid microspores - meiosis I and II, each followed by cytoplasmic division, results in four haploid (n) microspores. 3. Microspores undergo mitosis to form pollen grains - mitosis in a microspore results in a two-celled haploid body (a pollen grain). One cells will give rise to a pollen tube. The other cell will develop into a sperm-producing cell.  POLLEN GRAIN DEVELOP WITHIN POLLEN SACS IN THE ANTHERS Young pollen sac with numerous microsporocytes --- > microsporocytes --- meiosis --- > microspores (4) --- > single microspore --- mitosis --- > pollen grains (immature male gametophyte – generative cell (will divide to form sperm cells & tube cell) FIGURE 3: The development of pollen in the pollen sac on the anther.  Eggs Formation 1. An ovule forms in the ovary of a flower of the mature sporophyte. 2. Cells devides by meiosis – meiosis I and II, each followed by cytoplasmic division, result in four haploid (n) megaspores. 3. Three megaspores disintegrate. 4. Mitosis occurs in the remaining megaspore, without cytoplasmic division. 5. After two more rounds of mitosis with no cytoplasmic division, the megaspore ends up with eight haploid nuclei. 6. Cytoplasmic division results in seven-cell embryo sac. Six of those cells have a single nucleus, but one cell has two nuclei (2n). EMBRYO SAC DEVELOPS WITHIN THE OVULE Young ovule (megasporangium) --- > megasporocyte --- meiosis --- > functional megaspore & 3 disintegrating megaspores --- mitosis 3 divisions --- > embryo sac (female gametophyte) – antipodal cells + polar nuclei in a central cell + synergids + egg. &  Plants and Pollinators Pollen had evolved by 390 million years ago – Sperm packed inside a nutritious package – Transferred first by wind currents – Later transferred by insects Plants that attracted insect pollinators with flowers had a reproductive advantage  Pollination Transfer of pollen grains to a receptive stigma Pollen can be transferred by a variety of agents When a pollen grain lands on the stigma it germinates  Double Fertilization A pollen tube grows down through the ovary tissue It carries two sperm nuclei When pollen tube reaches an ovule, it penetrates embryo sac and deposits two sperm One fertilizes the egg, other fuses with both nuclei of endosperm mother cell  Endosperm Formation Occurs only in angiosperms Fusion of a sperm nucleus with the two nuclei of the endosperm mother cell produces a triploid (3n) cell This cell will give rise to the endosperm, the nutritive tissue of the seed  Seeds and Fruits The seed is the mature ovule The fruit is the mature ovary  Seed Formation Fertilization of the egg produces a diploid sporophyte zygote The zygote undergoes mitotic divisions to become an embryo sporophyte Seed: A mature ovule, which encases an embryo sporophyte and food reserves inside a protective coat  Structure of a Seed Protective seed coat is derived from integuments that enclosed the ovule Nutritious endosperm is food reserve Embryo has one or two cotyledons – Monocot has one – Dicot has two  Nourishing the Embryo Dicot embryo – Absorbs nutrients from endosperm – Stores them in its two cotyledons Monocot embryo – Digestive enzymes are stockpiled in the single cotyledon – Enzymes do not tap into the endosperm until the seed germinates  Fruit: A Mature Ovary Simple fruit – Derived from ovary of one flower Aggregate fruit – Derived from many ovaries of one flower Multiple fruit – Derived from ovaries of many flowers Accessory fruit – Most tissues are not derived from ovary  Aggregate Fruits Formed from the many carpels of a single flower Made up of many simple fruits attached to a fleshy receptacle Blackberries and raspberries are examples  Multiple Fruits Formed from individual ovaries of many flowers that grew clumped together Examples: – Pineapple  Seed Dispersal Fruit structure is adapted to mode of dispersal Some modes of seed dispersal: – Wind currents – Water currents – Animals  GLOSSARY 1. Parthenogenesis - A process in which the egg develops without being fertilized – Daphnia, bees, wasps, ants; A type of reproduction in which females produce offspring from unfertilized eggs. 2. Stolon - a creeping horizontal plant stem or runner that takes root at points along its length to form new plants. 3. Apomixis - the asexual production of seeds. 4. Ovule – a structure that houses a female gametophyte and that may become a seed. 5. Double fertilization - A process in the flowering plants life cycle in which there are two fertilizations; one fertilization results in formation of a zygote, whereas the second results in formation of endosperm. 6. Gamete – a sex cell – an eggs and sperm. 7. Parthenocarpy is the natural or artificially induced production of fruit without fertalization of ovules, which makes the fruit seedless.  DISCUSSION QUESTIONS Asexual reproduction 1. Describe parthenogenesis in plants. 2. Describe how the following structures may be used to propagate plants asexually: rhizomes, tubers, stolons, corms and bulbs. Sexual reproduction 1. Draw and label the parts of a flower, and describe the functions of each part. 2. Explain the development of pollen grains. 3. Explain the development of the embryo sac and ovum. Good luck