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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.