Angiosperm Reproduction

http://www.physicalgeography.net/fundamentals/images/angiosperm2.jpg

SeedDouble Fertilization

The union of two sperm cells with different nuclei of the embryo sac. Makes the embryo and the endosperm

EndospermFood storing tissue of

the seed.

http://www.learner.org/channel/courses/essential/life/images/show4.open_seed.jpg

Seedhttp://students.usm.maine.edu/deidre.rice/seed.JPG

Seeds and Eggs Seeds are plant products

which encloses the embryo with a hard coat and food supplies.

Eggs are animal products which enclose an animal embryo with a hard or leathery shell and food supply.

Eggs are similar to seeds because they protect the embryo while allowing gas exchange

From Ovule to SeedAfter Double Fertilization, each ovule develops

into a seed.

These seeds carry enough food and supplies until germination period.

Seeds sinks down because the Endosperm is filled with the heavy supplies.

Cotyledons swell to show that the Endosperm is filled with nourishment.

EndospermAn example of liquid Endosperm are the

coconut milk.

An example of solid Endosperm is the coconut meat itself. Also the white puff inside the popcorn is also the endosperm.

Seeds carry endosperms until they are mature enough

Endosperm Developmenthttp://www.niles-hs.k12.il.us/amilef/APReviewOut/SwatiCh38/SwatiChapter38_files/image008.jpg

Development of Plant Embryo

http://www.nicertutor.com/doc/class/bio1152/Locked/media/ch38/38_07EudicotEmbryogenesis.jpg

Structure of a Mature Seed

Dehydrated and enclosed with a seed coat.

HypocotylWhere cotyledons are attached

EpicotylConsists of the shoot tip and a pair of mini

leaves.

Seed Structurehttp://www.starkliteraria.com/dicotseed.gif

FruitsFruits protects the seed by aiding in dispersal by

wind or animals.

Fruits are products of matured flowers.

If the flower is not pollinated, then it just withers and falls of the tree.

Fruits usually dries up as the seed inside matures. Its because of the enzymes digesting the cell walls of the fruits, in other words, the mature the fruit is, the sweeter it is because of many starch are converted to sugar.

Kinds Of Fruit

Simple Fruit

http://65.214.37.88/ts?t=1274929236378461867

Aggregate Fruits

http://www.tarleton.edu/~range/Sanderson/02066%20aggregate%20fruit%20blackbery.jpg

Multiple Fruits

http://65.214.37.88/ts?t=14626671592156387751

Seed GerminationWhen seeds mature, they dehydrate and

went into a coma state called dormancy.

Being dormant means that the cell has low metabolic state.

Until the environment provides a suitable condition, the seed will remain dormant.

Dormancy is an evolutionary step because it promotes seed life by making it go to sleep and wakes up when the time is right.

Seed to SeedlingImbibition is that state when the seed wakes up

from dormancy and starts the intake of water.

It causes the seed to expand and ruptures, releasing the shoot, the cotyledons and the stalk.

It is the first sign of life after the dormant state.

Seed to Seedlinghttp://students.usm.maine.edu/deidre.rice/_ILLUS_ILT_T630888A.GIF

Asexual Reproduction: plant cloning

• Asexual reproductions results in exact clones of the parent, where sexual reproduction generates the genetic variation that contributes to evolutionary adaption.

• Some plants still use meiosis during the process of asexual reproduction, and some just perform mitosis.

•Also known as vegetative reproduction.

Mechanisms of Asexual Reproduction

• Plants have meristematic tissues of dividing, indifferentiated cells.

•These cells can sustain or renew growth indefinitely.

•Parenchyma cells throughout the plant can divide and differentiate into more specialized types of cells (regeneration of lost parts)

•Fragmentation is the separation of a parent plant into parts that develop into whole plants.

•Apomixis is the asexual reproduction of a seed. (different from fragmentation.)

•A diploid cell in the ovule gives rise to the embryo, the ovule matures into seeds, and are either dispersed or grow on the spot.

Hereditary testing of apomixishttp://www.uaf.edu/grnhouse/images/gary.jpg

Vegetative Propagation and Agriculture

•Asexual reproduction has been harnessed by farmers to enhance harvests.

•Many gardeners use cuttings, or fragments of plants, to produce clones. These fragments usually come from the shoot or stem of the plant.

•A callus forms at the open end of the fragment, followed by the growth of roots. If the fragment includes a node, then it skips the callus stage.

Grafting

•Grafting makes it possible to combine the best qualities of different species or varieties into a single plant.

• A twig or bud from one plant is grafted onto a plant of a closely related species or a different variety of the same species.

•Usually done in young plants.

•Plant receiving part is the stock, twig grafted onto the stock is the scion.

http://agspsrv34.agric.wa.gov.au/agency/images/4332046.jpg

This plant was grown from a tissue culture.

Artificial Selection• Natural Hybridization of plants is common in nature and is exploited by farmers to produce better plant products.

•Ex: maize

teosinte.wisc.edu/.../Maize-teosinte.jpg

Reducing World Hunger and Malnutrition/The Debate over plant

Biotechnology

• Genetically modified plants have the power to decrease world hunger by growing in more diverse landscapes and being altered to have more nutritional value.

•Ex: “Golden rice” versus ordinary rice. • Golden color and increased nutritional value of golden rice is a result of the production of beta-carotene. This was made possible by genetic engineering.

• Risks of GM plants: transporting allergens, effects on nontarget organisms, and the escaping of virus/herbicide resistant genes to neighboring weed. •So far, the good seems to outweigh the bad.

Haploid and Diploid Generations take turns producing each other

diploid, or sporpohyte, produces haploid spores by mitosis

The spores divide giving rise to gametophytes

Fertilization produces diploid zygotes which divide forming new sporophytes

The sporophyte generation is the dominant generation because they are the largest living plantsThey develop into flowers

The gametophytes shrink over time They rely on the sporophytes for nutritional

purposes

FlowersMale and Female gametophytes develop the

anthers and ovules

In pollination the sperm is brought to the ovule which contains the female gametophyte

The actual fertilization occurs within the ovule of the ovary which develops seedsThis allows the ovary to become a fruit

Flower Structure

Four main organs: sepals, petals, stamens, and carpels

Stamens and carpels are reproductive

Sepals and petals are sterile

If two or more carpels are present they conjoin resulting in a many chambered ovary

Anther: stalk like structure; ovary located at base

Stigma: collects pollen

Sepals enclose the floral bud serving as protection before opening

http://images.google.com/imgres?imgurl=http://andromeda.cavehill.uwi.edu/

Gametophyte Development and Pollination

Sporangia- structure on the anther and ovules where spores are produced

Pollen grains are made up of mature male gemetophytes that are enclosed by a spore wall

Found in the microsporangia, or pollen sacs

The female gametophyte is found within the ovule

Pollination is the transfer of pollen from anther to stigma Results if a pollen tube structure Purpose is to grow and digest down ovary and to

release sperm within embryo sacThis fertilizes the egg Embryo -> seed -> fruit containing seedThe fruit disperses seeds which germinate and

develop into seedlings

DevelopmentMicrosporocytes form four haploid microspores

These develop into haploid male gametophytes The microspore does through mitosis and

cytokinesis This results in a generative cell and tube cell

which make up the pollen grain

Megasporocytes grows resulting in four haploid megaspores

In some species the megaspore grows and divides by mitosis but not cytokinesis May form a multicellular female gametophyte

Contains 3 cells: 1 egg and 2 synegrids Synegrids attract and guide pollen tubes to the embryo

sac there are also two nuclei at the other end of the cell that

are not separate and share cytoplasm embryo sacsThese result in two integuments that form a seed

Mechanisms that Prevent Self-Fertilization

Sexual reproduction ensures that there will be genetic diversity among offspring

“Selfing” refers to self-fertilization in plantsEnsures that seed will develop

Ensuring that the egg and sperm cells come from different parents is a mechanism that inhibits self fertilization

Dioecious plants cannot self fertilize because they have either staminate or carpellate flowers

Flowers with functional stamen and carpels have organs that mature at different ratesAn animal pollinator would not transfer pollen from

the anther to a stigma of the same flower

Self IncompatibilityThe ability of a plant to reject its own pollen

Also, in some cases, the pollen of similar plants

If pollen were to land on the stigma of a flower on the same plant a biochemical would prevent the pollen from developing and fertilizing an egg

The S gene Two types of self-incompatibility

GametophyticSporphytic

GemetophyticS- allele blocks fertilization

S1 pollen grain from S1S2 parent will not fertilize the egg of an S1S2 flower

It will however fertilize the egg of and S2S3 flower

The RNA hydrolyzing enzymes will destroy the RNA if it enters the pollen tube

SporophyticS-allele gene produced in tissues of parental

sporophyte blocks fertilization

S1 and S2 pollen grains from S1S2 parents cannot fertilize eggs of S1S2 flowers or S2S3 flowers

Involves a signal transduction pathway in the epidermal cells Prevent germination of pollen grain

Special CircumstancesPlant breeders will hybridize different crop

varieties to combine the best traits and to get sufficient results

This can result in inbreeding

May cause plants that are able to self fertilize to lose that characteristic.