sexual reproduction in angiosperms
TRANSCRIPT
Sexual ReproductionIn Flowering Plants
Aesthetic, Ornamental, Social, Religious and Cultural value
FLOWER – A FASCINATING ORGAN OFANGIOSPERMS
Hormonal and structural changes
Floral primordium Inflorescences Flowers Androecium-
Stamens Gynoecium-
Carpels
Flower
L.S. of Flower
Pre fertilisation Fertilisation Post fertilisation
Sexual Reproduction
Stamen, Microsporangium and Pollen Grain
Bilobed Dithecous longitudinal groove four-sided
(tetragonal) four
microsporangia (pollen sacs)
Anther: Structure
four microsporangia
Epidermis Endothecium Middle layers Tapetum Sporogenous tissue
Anther wall layers
Microsporogenesis
sporogenous tissue
sporogenous cell (2n)
microspore tetrad (n)
Microspores/pollen grains (n)
Exine- Sporopollenin
Intine Vegetative cell Generative Cell Germ pores Pollen tube
Pollen/microspore
Resistant to
High temperatures Strong acids and alkali Enzymes
Sporopollennin
In over 60 per cent of angiosperms, pollen grainsare shed at this 2-celled stage
severe allergies Bronchial afflictions chronic respiratory disorders– asthma,
bronchitis Parthenium or carrot grass- Pollen allergy
Pollen grains
rich in nutrients pollen tablets as food supplements tablets and syrups to increase the performance of athletes and
race horses
pollen grains of a large number of species are stored for years in liquid nitrogen (-196ºC)
Pollen banks
Stigma Style Ovary
Pistil/Carpel
Monocarpellary
Syncarpous
Multicarpellary
Apocarpous
Carpels
Megasporogenesis
Megasporogenesis
Megasporogenesis
Pollen Pistil Interaction a continuous dialogue between pollen grain
and the pistil mediated by chemical components of the
pollen and the pistil wrong type (incompatible): Rejected right type (compatible) of pollen pollen germination on the stigma pollen tube through germ tube
Double Fertilisation
Emasculation: Removal of anthers from the flower bud before the anther dehisces
Bagging Collected pollen dusted on stigma Rebagged
Artificial Hybridisation
POST-FERTILISATION : STRUCTURES AND EVENTS
PEN Endosperm (3n)
Egg Zygote (2n) Embryo
PEN Free nuclear divisions free-nuclear endosperm Subsequent cell wall formation Cellular endosperm Coconut water: free-nuclear endosperm White kernel: cellular endosperm
Endosperm Development
Embryo Development
Embryo
Fertilised ovule Non-Albuminous or Albuminous Perisperm: persistent nucellus Seed Dormancy
The Seed
Fleshy fruit/Dry fruit Fruit wall- Pericarp Pericarp- Epicarp, Endocarp, Mesocarp False fruits/True fruits Parthenocarpic fruits: developed without
fertilisation
Fruits
more dependable dispersal to new habitats sufficient food reserves The hard seed coat: Protection Variations
Seed: Advantages
Seed development without fertilisation
Diploid egg Embryo
Nucellar cells protrude into the embryo sac and develop into the embryosPolyembryony
Apomixis
Transfer of pollen from anther to the stigma Autogamy Geitonogamy Xenogamy Chasmogamous and cleistogamous flowers
Pollination
wind
Water
animals
Agents of Pollination
light non-sticky well-exposed stamens large often-feathery stigma single ovule in each ovary Inflorescence common in grasses
Wind pollination
limited to about 30 genera mostly monocotyledons distribution is limited because of the need for water for
transport of male gametes Vallisneria, hydrilla- freshwater forms Zostera- marine Vallisneria- water surface Sea grasses- inside water Water hyacinth, water lilly – wind and insects long, ribbon like pollen Pollen grains have mucilaginous covering not colourful Do not produce nectar
Water pollination
Colour and/fragrance foul odours Nectar and pollen grains-floral rewards providing safe places to lay eggs
Amorphophallus moth and the Yucca relationship
Animal pollination
To overcome inbreeding depression Pollen release and stigma receptivity not
synchronised Anther and stigma placed at different
positions Self incompatibility Production of unisexual flowers Monoecious/dioecious condition
Outbreeding Devices