Transcript Seed - DavisonScience

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/imag
es/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
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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/0206
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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
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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.
This plant was grown from a tissue
culture.
http://agspsrv34.agric.wa.gov.au/agency/images/4332046.jpg
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
 Anther: stalk like
structure; ovary located at
base
 Stigma: collects pollen
 Sepals enclose the floral
bud serving as protection
before opening
 If two or more carpels are
present they conjoin
resulting in a many
chambered ovary
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 SelfFertilization
 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.