Pollination and Fertilization PDF

POLLINATION AND FERTILIZATION Mrs. Mithila. A. Vivalkar  POLLINATION The process of the transfer of pollen grain from the anther to the stigma  TYPES OF POLLINATION Self pollination...

POLLINATION AND FERTILIZATION Mrs. Mithila. A. Vivalkar  POLLINATION The process of the transfer of pollen grain from the anther to the stigma  TYPES OF POLLINATION Self pollination Cross-pollination or Allogamy Autogamy Geitonogamy The pollen of a flower of another plant of the same species may fall on its stigma by itself The pollen of the same flower The pollen of another flower of may fall on its stigma by itself the same plant may fall on the stigma  SELF POLLINATION Transfer of pollen from the anther to the stigma of the same flower or to the stigma of another flower of the same plant. The general qualities or features of any one plant are the same in the different flowers borne on it. Cleistogamy – some flowers growing close to the ground level, do not open at all, their anthers lie close to the stigma and are self pollinated when matured. E.g. peanuts and peas Occurs in bisexual flowers, or bisexual plant which has both male and female flower on the same plant Advantages of self-pollination Pollination is guaranteed as both the stamen and carpels mature together. Parental characters are preserved indefinitely. No wastage of pollen grain. The flower need not be large and showy Scent and nectar need not be produced by flowers A great economy on the part of the plant Disadvantages of self-pollination Weakening of the variety or the species, poor quality of seeds are produced which gives rise to less vigorous offsprings. The weaker or defective characters of the variety or breed cannot be eliminated It does not yield new varieties. CROSS- POLLINATION Transfer of pollen from the anther of flowers of one plant to the stigma of flower of another plant of the same species. Advantages of Cross-pollination The off-springs are healthier The seeds produced are abundant and viable. New varieties may be produced by cross pollinating two different varieties of the same species. Disadvantages of Cross-pollination Pollination is not always certain. Wastage of pollens, as a large number of pollens have to be produced to ensure chances of pollination The process is uneconomical for the plant, because the flowers have to be large, coloured, scented and have to produce nectar- for attracting pollinating agents. Conditions favoring Cross-pollination 1. Unisexuality – male and female flowers are borne on separate plants, e.g. Palms and Papaya or male and female flowers are bone on the same plant, e.g. Cucumber 2. Dichogamy – timing of maturation is different for androecium and gynoecium. a) Protandry – anthers mature earlier than stigma, e.g. Sweet pea, ladyfinger, sunflower. b) Protogyny – stigma matures earlier than the anther, e.g. custard apple, peepal. 3. Self sterility – pollen from only another plant of the same species fuse with stigma of a flower, e.g. ray florets of sunflower, orchids 4. Herkogamy – In some flowers there may be some physical barrier between the anther and the style so that pollination between them is rendered difficult or even impossible. E.g. Calatropis, Iris etc 5. Heterostyly – In some flowers the anthers and stigma grow at a different height which does not favour self pollination. E.g. Primrose  Agents of Cross-pollination Abiotic agent Biotic agent Wind / Anemophily Water / Hydrophily Insect / entomophily Artificial pollination Anemophilous flower Hydrophilous flower Entomophilous flower Birds / Ornithophily Ornithophilous flower  Wind pollination / Anemophily Flowers are small , not brightly coloured and often dull green Do not produce scent or nectar Stamens are long and hang out of the flower Anthers are large and loosely attached Pollen grains are produced in vary large quantities Pollen are light, dry and smooth Stigma is feathery and hang out from the flower Water pollination / Hydrophily Pollen grains are produced in large numbers Pollen have specific gravity so that they float on water In some cases male flowers are such that they float on the surface of water till they meet female flowers. Eg vallisneria. Insect pollination / Entomophily Flowers are large, brightly coloured, emit scent, produce nectar. Pollen grains are sticky or spiny Stigma is sticky and does not hang out from the flower Pollination by Birds / Ornithophily – e.g. Bignonia, Canna, Bombax Pollination by Elephants / Elephophily – e.g. Rafflesia Pollination by Bats / Chiropterophily – e.g. Anthocephallous (kadamb), Bauhinia Artificial Pollination When man himself transfer the pollens to stigma. E.g. Babylonia Crossing over is done, and new variety is produced.  FERTILIZATION It is the fusion / union of the nuclei of male and female gamete. Fertilization Pollen grain Ovule (male gamete) (female gamete) Fuse to form Zygote Embryo New baby plant The Pollen grain Formation of pollen tube on stigma The Ovary and Ovule (3 cells) (1 cell) (2 cells) Double fertilization 1. One sperm nucleus fuses with the egg cell nucleus 2. The other sperm nucleus fuses with two polar nuclei together Fate of floral parts after fertilization