4/14/2011

1

Plant Reproduction

Prepared by Diana Wheat

For LBCC – General Biology 103

Revised Spring 2011

Objectives

� To define the alternation of generations.

� To explain how pollination leads to fertilization.

� To address double fertilization.

� Introduce anatomy of a flower

� Relate fruits & seeds to flower.

� Classify different fruit types.

� Address seed dispersal

Now onto plants

Alternation of generations

The life cycle typically found in

plants in which the spore producing generation alternates with the

gamete producing generation.

Plants have 2 forms…….

The different forms

Gametophyte: The multicellular, haploid stage in the life cycle of

plants.

Sporophyte: The diploid form of a

plant that produces , haploid, asexual spores through the process

of meiosis – reduction division.

Flower are modified structures

Innovations for reproduction.

Flower Anatomy

� Sepals, which enclose

the flower

� Petals, which are brightly colored and

attract pollinators

� Stamens, which

produce pollen

� Carpels, which produce ovules

4/14/2011

2

The Angiosperm Life Cycle

In the angiosperm life cycle

� Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule

� One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates

development of food-storing endosperm

The endosperm

� Nourishes the developing embryo

The Participants

Pollen: Male gametophyte of seed plants.

Ovule: Female gametophyte of seed plants.

The ProductsThe Products

Seed Seed –– From the ovuleFrom the ovule

Seed Coat Seed Coat ––

From the Ovule WallFrom the Ovule Wall

Fruit Fruit –– From the OvaryFrom the Ovary

Life Cycle: Eudicot

Pollen sacs form in the mature sporophyte.

pollen sac anther (cutaway view)

filament

meiosisDiploid Stage

Fig. 30-8 (a-d), p. 512

Stepped Art

Haploid Stage

A pollen grain released from the anther lands on a stigma and germinates.

pollen tube

stigmaMature Male Gametophyte

carpelsperm cells (male gametes)

Double fertilization Double fertilization results from the results from the discharge of two sperm from the discharge of two sperm from the pollen tube into the embryo sacpollen tube into the embryo sac

One sperm One sperm �� the the eggegg

The other combines with the polar The other combines with the polar nuclei in ovule foodnuclei in ovule food--storing storing …………………………….…………………………….endosperm.endosperm.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4/14/2011

3

Fig. 30-8 (e-i), p. 513

an ovuleovary wall

cell inside ovule tissueSporophyte

seedling (2n)

seed coatembryo (2n)

In a flower of a mature sporophyte, an ovule forms inside

an ovary. One of the cells in the ovule enlarges.

ovary (cutaway view)

Diploid Stagedouble fertilization meiosis

Haploid Stage

pollen tube

Female Gametophyte

endosperm mother cell (n + n)

egg (n)

The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.

endosperm (3n)

Flower Sex

� Recognition proteins on epidermal cells of the stigma bind to molecules in the pollen grain coat

� Species-specific molecular signals from the stigma stimulate pollen germination and guide pollen-tube growth to the egg

Life Cycle: EudicotType of flowers

Regular vs. Irregular - Symmetry

Complete vs. Incomplete - # whorls

Perfect vs. Imperfect – if both M & F

Inflorescence - Clusters

4/14/2011

4

Now let’s revise our model

1) How does the pollen take the sperm to the egg?

2) Where is the seed?

3) What part will become the fruit?

Pollination

The transfer of pollen from anther to stigma.

Cross pollination (dioecious plants)vs. Self pollination (monecious).

For discussion:Advantages?Disadvantages?

Why use animals as

agents of pollination?

Answer:

� There is a high degree of pollinator

specificity.

Plants attract animals using a variety of adaptations including:

> Color

> Scent

> Heat

> Rewards (pollen & nectar) The goods!

Special Features

Thermogenic – in cold climates

Nectar guides – UV reflected “runways.”

Landing platforms – umbels or large petals

Unusual shapes – usually in the tropics

Pheromones – sex attractant mimics

What a bee can see……

Fruit adaptations help disperse seeds

Seeds can be carried by:

> wind

> water

> animals

…………..to new locations

Adaptations for Fruit Dispersal

4/14/2011

5

Fruits

� Consists of a mature ovary but can also include other flower parts

� Fruits protect seeds and aid in their dispersal

� Mature fruits can be either:

I. Fleshy - eg: grapes, apricots,apples

II. Dry – eg: beans, grains, nuts

Simple Fruits

� Develops from a single carpel.

OR

� May develop from several fused carpels.

� Derived from one flower.

� Examples: Pea, lemon, beans, peanut.

Aggregate Fruit

� Develops from many separate carpels.

� From one flower.

� Examples:

- raspberry

- blackberry

- strawberry

Multiple Fruits

� Develops from many carpels.

� Many flowers i.e. an inflorescence.

� Examples:

� Pineapple.

� Fig

Accessory Fruit

� Develops from tissues other than the ovary.

� May be embedded

in the fleshy receptacle.

� Examples:

- Apple (only core develops from ovary).

4/14/2011

6

Impacts, Issues

Plight of the Honeybee

� Flowering plants coevolved with animal pollinators such as honeybees – now pesticides and other factors threaten our food supply