Angiosperm Reproduction

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

Seed   Double Fertilization

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

  Endosperm   Food storing tissue

of the seed.

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

Seed http://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 Seed   After 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.

Endosperm   An 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 Development http://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.

 Hypocotyl   Where cotyledons are attached

  Epicotyl   Consists of the shoot tip and a pair of mini

leaves.

Seed Structure http://www.starkliteraria.com/dicotseed.gif

Fruits   Fruits 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

Seed Germination  When 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 Seedling   Imbibition 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 Seedling http://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 apomixis http://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 plants   They develop into flowers

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

Flowers   Male 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 seeds   This 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 sac

  This fertilizes the egg   Embryo -> seed -> fruit containing seed

  The fruit disperses seeds which germinate and develop into seedlings

Development   Microsporocytes 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 sacs

  These 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 plants   Ensures 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 rates   An animal pollinator would not transfer pollen from

the anther to a stigma of the same flower

Self Incompatibility   The 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

  Gametophytic   Sporphytic

Gemetophytic   S- 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

Sporophytic   S-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 Circumstances   Plant 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.