1. Pre-Fertilisation: Structures and Events

Before a flower even appears, the plant has already decided to bloom! 🌱 Hormonal and structural changes kickstart the formation of floral primordia, leading to inflorescences and eventually, the flower itself. The flower has two main reproductive parts:

  • Androecium – the male part (stamens)
  • Gynoecium – the female part (pistils)

2. Stamen, Microsporangium and Pollen Grain

A typical stamen has two parts:

  • Filament – long and slender stalk
  • Anther – usually bilobed, contains pollen sacs

Anthers have four microsporangia where pollen grains develop. They eventually become pollen sacs packed with thousands of pollen grains. 🧡

🔬 Microsporogenesis

Inside each microsporangium, cells called sporogenous tissue undergo meiosis to produce microspore tetrads:

\[ \text{Microspore Mother Cell (2n)} \xrightarrow{\text{Meiosis}} \text{Microspore Tetrad (n)} \]

These microspores separate and mature into pollen grains.

🧬 Pollen Grain Structure

  • Exine: Hard outer layer made of sporopollenin (super tough!)
  • Intine: Inner wall made of cellulose and pectin
  • Contains two cells when mature: vegetative and generative

Pollen grains can remain viable from 30 minutes (like in rice) to several months (like in legume plants)! 🕒❄️

3. Pistil, Ovule and Embryo Sac

The pistil has three parts:

  • Stigma – landing site for pollen
  • Style – slender stalk
  • Ovary – contains ovules

Each ovule is attached by a funicle and has layers called integuments. The small opening is called the micropyle.

🌱 Megasporogenesis

From one megaspore mother cell (MMC), meiosis produces four megaspores:

\[ \text{MMC (2n)} \xrightarrow{\text{Meiosis}} \text{4 Megaspores (n)} \]

Only one becomes functional and develops into the female gametophyte (embryo sac).

🎀 Embryo Sac Formation

The functional megaspore’s nucleus divides mitotically to form:

  • 2-nucleate → 4-nucleate → 8-nucleate stages
  • 7 cells in total:
    • 3 cells at micropylar end → Egg Apparatus (2 synergids + 1 egg)
    • 3 cells at chalazal end → Antipodals
    • 1 large central cell with 2 polar nuclei

4. Pollination 🌼

Pollination is the transfer of pollen from anther to stigma.

Types of Pollination:

  1. Autogamy – Same flower 🌸
  2. Geitonogamy – Different flower on same plant 🌿
  3. Xenogamy – Different plant 🌱🌱

Pollination Agents:

  • Abiotic: Wind 🌬️, Water 💧
  • Biotic: Insects 🐝, Birds 🐦, Bats 🦇

Cool Adaptations:

  • Wind: Lightweight, non-sticky pollen; feathery stigma
  • Water: Ribbon-like pollen, mucilaginous coating
  • Animals: Colorful, nectar-rich flowers

5. Outbreeding Devices 💡

To prevent inbreeding, plants have cool tricks:

  • Differential timing of pollen release and stigma readiness
  • Different positions of anther and stigma
  • Self-incompatibility – genetic mechanism that rejects self-pollen
  • Unisexuality (e.g., papaya)

6. Pollen-Pistil Interaction 🌟

The stigma can recognize if the pollen is from the same species (compatible) or not (incompatible). If compatible:

  • Pollen germinates on stigma
  • Pollen tube grows through style to ovule
  • Enters synergid through micropyle using the filiform apparatus

In two-celled pollen: generative cell divides during tube growth. In three-celled pollen: both male gametes are ready. One fertilizes the egg; the other fuses with polar nuclei. 🌟

7. Artificial Hybridisation 🌾

  • Emasculation – Removing anthers from bisexual flowers
  • Bagging – Covering flower to prevent unwanted pollen

This is widely used in crop improvement. 🎯