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