Fertilisation in Plants

1
Fertilisation in Plants

• Concluding Plant Reproduction

2
Plant fertilisation

• When pollen sticks to the stigma it absorbs water
  and starts to germinate
• A pollen tube will grow out of the grain and
  through the style towards the ovary

3
Plant fertilisation

• The pollen tube nucleus remains close to the tip
  of the tube.
• Digestive enzymes are secreted from the tube.
• The tube is attracted by chemicals given out by
  the ovary.

4
Plant fertilisation

• As the tube grows the generative nucleus divides
  by mitosis to form two haploid male gametes.

5
Plant fertilisation

• The pollen tube enters the ovule through the
  micropyle.
• Once inside the ovule the tube nucleus
  degenerates and the male gametes enter the embryo
  sac

6
Plant fertilisation

• One of the male gametes fuses with the female
  gamete forming a diploid zygote.
• In plants a double fertilisation takes place as
  the other male gamete fuses with the diploid
  nucleus in the centre of the embryo sac forming a
  triploid nucleus called the endosperm nucleus.

7
Outbreeding mechanisms

• How plants prevent self-fertilisation

8
Protandry

• Most flowers use this mechanisms, e.g. rose-bay
  willowherb
• The stamens ripen before the stigma is receptive
  to pollen.
• So pollen is gone by the time stigma is ready.

9
Protogyny

• More unusual than protandry e.g. the bluebell
• The stigma ripens before the anthers.
• By the time the anthers shed their pollen the
  stigma is no longer receptive to it.

10
(No Transcript)
11
Dioecious Plants

• With dioecious plants each individual plant bears
  either male or female flowers, but never both.

12
Dioecious Plants

• Paw-paw and holly are examples of dioecious
  plants.
• Clearly self-pollination is impossible!