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Flowers. Remember …. Three more differences between gymnosperms and angiosperms. 4. Angiosperm ovules are protected within an enclosed structure rather sitting on a modified leaf. 5. Double fertilization in the angiosperms produces a diploid zygote and triploid endosperm nucleus.

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slide2

Remember …

Three more differences between gymnosperms and angiosperms

4. Angiosperm ovules are protected within an enclosed structure rather sitting on a modified leaf

5. Double fertilization in the angiosperms produces a diploid zygote and triploid endosperm nucleus

6. In the angiosperms there are generally hermaphrodite flowers and cross pollinating (70%). Wind pollination is typical in the gymnosperms animal pollination widespread in angiosperms

First some basic naming of parts

basic structure of the angiosperm flower
Basic structure of the angiosperm flower

STAMEN

(male reproductive part)

CARPEL

(female reproductive part)

filament

anther

stigma

style

ovary

OVULE (forms within ovary)

petal (all petals combined are the flower’s corolla)

sepal (all sepals combined are the flower’s calyx)

receptacle

This is a hermaphrodite flower with a single carpel

Fig. 31.3, p. 532

slide4

Collective nouns that can cause confusion!

Calyx

The outer whorl of a flower made up of sepals that are usually green, and protect the flower in bud.

Carpel

Bears the stigma, and frequently an elongated style, and encloses the ovules (sometimes gynaecium). The megasporophyll of the flower

Corolla

The collective term for the petals of a flower

slide5

Collective nouns that can cause confusion!

Ovary

The total of the carpels in a flower is the ovary

Perianth

The floral envelope, it includes the calyx and corolla.

Pistil

Each separate carpel when there are lots of them in the ovary

Stamen

The anther and its supporting filament. The microsporophyll of the flower

evolution of the pistil
Evolution of the pistil

4. Angiosperm ovules are protected within an enclosed structure rather sitting on a modified leaf

Remember, angeion case – this is how we think it evolved

life cycle of angiosperms
Life cycle of Angiosperms

BUT

mature sporophyte

seed

meiosis (within anther)

meiosis (within ovary)

DIPLOID

HAPLOID

fertilization

gametes (sperm)

microspores

(mitosis)

male gametophyte

gametes (eggs)

megaspores

female gametophyte

(mitosis)

The basic life cycle appears similar to that of the Gymnosperms …

there is a well developed receiving system for the pollen so that the male gametophyte can penetrate the angion,

the female gametophyte has a more complex structure that results in an endosperm, nutritive material for the embryo

overview of cherry life cycle
Overview of cherry life cycle

Flower

Ovule formation

Seedling

Seed

Diploid Stage

Meiosis

Meiosis

Double Fertilization

Haploid Stage

Pollen development

Development of embryo sac

Pollination

how pollen grains develop and germinate
How pollen grains develop and germinate

pollen sac

Anther

(cutaway view)

filament

one of the microspore mother cells inside a pollen sac

Meiosis I and II each followed by cytoplasmic division results in four haploid (n) microspores

Mitosis in a microspore gives a 2 celled, haploid, pollen grain. One cell will grow to be the pollen tube. The other will produce two sperm nuclei.

pollen tube

Pollen release

sperm nuclei

stigma

style of carpel

(see next slide)

Diploid Stage

Meiosis

Haploid Stage

(see next slide)

mature male gametophyte

Fig. 31.6a, p. 534

5 double fertilization in the angiosperms produces a diploid zygote and triploid endosperm
5. Double fertilization in the angiosperms produces a diploid zygote and triploid endosperm

Ways in which Angiosperms are different from Gymnosperms

slide11

Somatic cell division involves two successive steps:

mitosis and cytokinesis.

Now, remind me, what is cytokinesis again … ?

In mitosis, the nuclear DNA duplicates and chromosomes segregates equally between the two daughter nuclei;

cytokinesis divides these two nuclei and cytoplasm, including related cytoplasmic organelles, into two individual cells.

the fertilization process in angiosperms
The fertilization process in Angiosperms

an ovule

ovary wall

cell

integument

stalk

seed coat

seed

embryo (2n)

ovary (cutaway view)

endosperm (3n)

Meiosis I and II each followed by cytoplasmic division result in 4 haploid megaspores

3 megaspores disintigrate

pollen tube

embryo sac inside ovule

Three rounds of mitosis with NO CYTOPLASMIC DIVISION produces a megaspore with 8 haploid nuclei

endosperm

mother cell

(n + n)

integuments

egg (n)

seedling (2n)

How many ovules in a cherry?

Diploid Stage

Double Fertilization

Meiosis

Haploid Stage

One sperm nucleus to the egg, one to the endosperm mother cell

Cytoplasmic division then gives 7 cells – the endosperm mother cell with 2 nuclei

Fig. 31.6b, p. 535

what goes on in the endosperm
What goes on in the endosperm?

The triploid nucleus divides and the endosperm cell becomes a supercell with many nuclei and a milky consistency.

Cyotkinesis forms membranes and walls between the nuclei and makes the endosperm more solid.

In most dicots the developing embryo moves the nutrients stored in the endosperm to the cotyledons and the endosperm is not present in a mature seed.

In moncots the endosperm remains and is used by the seedling after germination.

slide15

6. In the angiosperms there are generally hermaphrodite flowers and cross pollinating (70%). Wind pollination is typical in the gymnosperms animal pollination widespread in angiosperms

Ways in which Angiosperms are different from Gymnosperms

HERMAPHRODITOS was one of the EROTES, and a handsome son of Hermes and Aphrodite. He was loved by the Nymphe Salmakis who prayed that she could be with him forever.

The gods, on hearing her prayer, merged their two forms into one, forming a being that was both male and female.

Hermaphrodite: organism with the organs of both sexes.

slide16

That should make fertilization easier. Pollen can fertilize the egg and endosperm mother cell of the same flower.

Hmm! I’m not so sure that is such a good idea.

How can self-fertilization be prevented for hermaphrodite flowers?

[1] Differences in timing of maturity of male and female parts

[2] Incompatibility mechanisms

pollen and stigma incompatibility
Pollen and stigma incompatibility

There can be dozens of alleles of the S-gene. If a pollen grain has an allele that matches an allele of the stigma upon which it lands, then the pollen tube fails to grow.

This system prevents self-fertilization AND fertilization from close relatives.

rye grass incompatibility
Rye grass incompatibility

Pollen Grain Size and Surface Morphology in a Perennial Rye Grass Hybrid

Attempts to hybridize between particular varieties resulted in production of a web-like substance and incompatibility

Pollen grain on stigma

Stacey Lacoste

the efficiency of animal pollination
The efficiency of animal pollination

Nucleus of tube cell

Generative cell

Its not just the honey guys!

Lilium pollen

Pollen is up to 30% protein

Animal pollination is targeted and so is more efficient than wind pollination.

Animal pollinated flowers generally produce much less pollen than wind pollinated flowers.

Pollen is important for animals – and many animal pollinated plants do produce some excess pollen.

http://www.uri.edu/artsci/bio/plant_anatomy/images/153.gif

reproduction and diversity of angiosperms
Reproduction and diversity of angiosperms

Animal pollination is efficient and associated with the development of the hermaphrodite reproductive axis

The diversity of flowers represent mechanisms promoting efficient pollination

Prevention of self-fertilization maintains genetic variation by promoting cross pollination

Sophistication of the reproductive process enables a large number of ways reproductive isolation can occur and so maintains genetic diversity