Adrienne Kurtz, Jeff Porter, Heather Cohen, Kim Shea

 The life cycles of plants are comprised of interval haploid and diploid generations, producing one another.
Diploid (sporophyte)-produce a flower
Produces haploid spores (by meiosis)
Spores undergo mitosis
Give rise to male and female haploid plants
Haploid plants become fertilized
Diploid zygotes that divide by mitosis=sporophytes-the dominant generation

Campbell Reece Biology Textbook, AP 7 th edition

Flower Organ
Sepals: a) Protect the floral bud before it opens. b) They are green, and leafy. c) Sterile.
Petals: a) These are the colorful tissues on the outside of the flower, which attract pollinators. b) Sterile.
Stamens: a) Pollen producing.
b) Consists of the filament (a stalk) and the anther (terminal structure that contains pollen producing sacs).
c) Reproductive organ.
Carpels: a) Ovule producing organ.
b) Consists of an ovary, a style (long slender neck), and a stigma (sticky structure that is a port for pollen to land on). c) Ovaries produce eggs. They also contain ovules.
d) A single carpel, or a group of fused carpels.
Complete flowers contain all four basic organs.
Incomplete flowers lack 1+ basic organs.

-Flowers can differ in symmetry.
-Depending on species, the ovary location can differ as well.
-Clusters of flowers known as inflorescences , or single flowers can exist on a plant.
-The functions of the different parts depending on the flower, can change the reproduction methods.

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Pollination is the transfer of pollen from an anther to a stigma.
MICROSPORES: Four haploid microspores are formed by a microsporocyte after meiosis.
-Undergoes mitosis and cytokinesis producing the generate and tube cells.
MEGASPORES: Four haploid megaspores are formed after meiosis, in the megasporangium of each ovule.
-Usually, only one megaspore survives.
Different methods of pollination are used, such as pollination by the bees, and birds, or air, or for water plants, water.

 Sexual reproduction is beneficial to genetic diversity. If plants reproduced always asexually, there would be no new genes ever introduced, unless a mutation occurred.
 Self-incompatibility: The ability of a plant to reject its own pollen, or related pollen, in order to receive new DNA instead.
 In gametophytic situations, the S allele governs self incompatibility, while in sporophytic cells, a signal transduction pathway is used.

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Humans have selected the best plants for their needs over thousands of years and created different genetic makeups.
Maize started from teosinte, a plant with loose kernels at maturity which made harvesting difficult, so farmers selected for a large kernel size which stayed attached to the cob.
Maize is used very commonly in developing countries but it is low in protein, except for a mutant variety called opaque-2.
-This mutant had high levels of lysine and tryptophan which promoted growth.
-Opaque-2 also have a soft endosperm which makes it difficult to harvest and more vulnerable to pests.
Modern plant biotechnologists are able to transfer genes between species that are unrelated without the use of intermediate species over a long period of time.

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Eight hundred million people suffer from malnutrition and forty thousand people died each day from malnutrition.
To feed an increase in population, a greater yield from the crops will be needed, and plant biotechnology can help with an increased yield.
Transgenic varieties of cotton, maize and potatoes contain Bacillus
thuringiensis, a gene that codes for the Bt toxin, which becomes toxic in alkaline conditions, such as in the guts of insects.
Creating transgenic plants that are resistant to herbicides allows farmers to get rid of weeds without having to till the soil which causes soil erosion.
The quality of plants can also be improved from adding in genes that produce vitamins and other nutrients.

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Genetic engineering may transfer allergens to humans from a plant that is used as food.
Genetic engineering may be safer to eat than non modified foods however, such is the case in maize with the Bt toxin because it contains 90% less of fumonisin, a mycotoxin which causes cancer.
People are still skeptical about genetically modified foods so any products containing the modified food has to be clearly marked.

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There was one Bt maize line which produced pollen with a high concentration of Bt toxins, but most varieties have the high concentration in the floral parts of the plant.
The alternative to the Bt maize would be to spray chemical pesticides on the crops which would be much more damaging to the ecosystem.

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It is possible that genes from a transgenic crop may escape onto related weeds through crop-to-weed hybridization.
If hybridization occurs with a crop, a “superweed” may occur and it may be difficult to control.
There is an effort being made to breed male sterility into transgenic crops to combat transgene escape.
“Terminator technology” would create “suicide” genes that disrupt development and activate a protein that’s toxic to the plant, but harmless to animals.

Offspring are formed from a single parent causing no genetic recombination. The parent passes on all of its alleles to its offspring, which results in a clone of the parent.
In plants, asexual reproduction is also called vegetative reproduction, because the offspring are mature vegetative fragments from the parent plant.
Asexual reproduction can be beneficial if the parent plant is suited to a stable environment.
Since its offspring will be clones of the parent, they will also be suited for the environment if conditions remain stable. In an unstable environment, asexual reproduction puts plants at risk for extinction if there is a significant environmental change.

Fragmentation Apomixis
• Parent plant is divided into parts that develop into whole plants
• One of the most common methods of asexual reproduction
• Example
- A severed stem can develop adventitious roots and become a whole plant
• Fragmentation has produced a ring of creosote bushes in California, the oldest of all known plant clones.
• Plants produce seeds without pollination or fertilization
• Has evolved in plants such as dandelions
• Uses seed dispersal
- A diploid cell in the plant ovule gives rise to an embryo
- The ovules mature into seeds
- In dandelions, the ovules are dispersed by windblown fruits.

• At the cut end of a shoot, a callus, or mass of dividing and undifferentiated cells, is formed.
- Adventitious roots develop from the callus
- If the shoot fragment has a node, the adventitious roots will form without a callous stage.
• In plants such as African violets, propagation can occur from single leaves rather than stems.
• In some plants, cuttings are taken from specialized storage stems.
- A potato can be cut into several pieces, each containing a vegetative bud. These buds will then regenerate the whole plant.

Vegetative Propagation and
Agriculture
• A twig or bud from one plant is grafted onto a plant of a different variety of the same species, or a closely related species.
• Makes it possible for the best qualities of each species or variation to be combined into one plant.
• The plant providing the root system is called the stock.
• The twig grafted onto the stock is called the scion.
• In some cases, grafting can alter the characteristics of the shoot system that develops from the scion.
- This happens in dwarf fruit trees

Vegetative Propagation and
Agriculture
Plants can be grown by culturing small explants, or even single parenchyma cells, on an artificial medium containing nutrients and hormones. These cells will divide and form an undifferentiated callus, as shown in the picture above.
When there is a hormonal balance in the culture medium, the callus can sprout roots and shoots with fully differentiated cells, as shown in the above picture. These plantlets are then transferred to soil, where they can continue their growth.

Vegetative Propagation and
Agriculture
• Transgenic
- Genetically modified organisms that have been engineered to express a gene from another species.
- Test tube culture makes it possible to regenerate these plants
• Protoplast Fusion
- Technique with tissue culture methods to invent new plant varieties that can be cloned.
- Protoplasts are plant cells that have had their cell walls removed by treatment with enzymes isolated from fungi.
- Before being cultured, protoplasts can be screened for mutations that may improve the plant’s agricultural value.
- It is sometimes possible to fuse two protoplasts from different plant species, and culture the hybrid protoplasts.
- This was successful in forming a hybrid between a potato and a wild relative called the black nightshade.

(Campbell & Reece, 2005)

Double fertilization ensures that the endosperm will develop only in ovules where the egg has been fertilized, thereby preventing angiosperms from squandering nutrients.
(Campbell & Reece, 2005)

 After double fertilization, each ovule develops into a seed, & the ovary develops into a fruit enclosing the seeds. As the embryo develops from the zygote , the seed stockpiles proteins, oils, & starch to varying extents, depending on the species. Initially, these nutrients are stored in the endosperm, but later in seed development in many species, the storage function of the endosperm is more or less taken over by the swelling cotyledons of the embryo.
(Campbell & Reece, 2005)

 Precedes embryo development.
 After double fertilization, the triploid nucleus of the ovule ′ s central cell divides & forms a multinucleate supercell having a milky consistency. The liquid mass, the endosperm, becomes multicellular. Cytokinesis partitions the cytoplasm & forms membranes between the nuclei. These cells produce cell walls, and the endosperm becomes solid.
(Campbell & Reece, 2005)

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1 st mitotic division of zygote is transverse & splits the fertilized egg into a basal cell & a terminal cell. The terminal cell gives rise to most of the embryo. The basal cell continues to divide transversely & produces a thread of cells called the suspensor. This anchors the embryo to its parent & functions in the transfer of nutrients to the embryo from the parent plant &, in some plants, from the endosperm. As the suspensor elongates, it pushes the embryo deeper into nutritive and protective tissues. Meanwhile, the terminal cell divides several times & forms a spherical proembryo attached to the suspensor.
(Campbell & Reece, 2005)

 The cotyledons begin to form as bumps on the proembryo. A eudicot, with two cotyledons, is heart– shaped at this stage. Only one cotyledon develops in monocots. Soon after the rudimentary cotyledons appear, the embryo elongates. The embryonic shoot apex is cradled between the cotyledons & includes the shoot apical meristem. At the opposite end of the embryo’s axis where the suspensor attaches is the embryonic root apex
& it includes the root apical meristem. After the seed germinates, the apical meristems at the tips of shoots & roots will sustain primary growth as long as the plant lives.
(Campbell & Reece, 2005)

(Campbell & Reece, 2005)
By the time the ovule becomes a mature seed & the integuments harden & thicken to form the seed coat, the zygote has given rise to an embryonic plant with rudimentary organs.

 During last stages of its maturation, a seed dehydrates until its water content is only about 5–15% of its weight.
The embryo, surrounded by a food supply (cotyledons
& endosperm), becomes dormant. The embryo & food supply are enclosed by a hard, protective seed coat formed from integuments of the ovule.
(Campbell & Reece, 2005)

The embryo consists of an elongate structure, the embryonic axis, attached to fleshy cotyledons. Below where the cotyledons are attached, the embryonic axis is called the hypocotyl. The hypocotyl terminates in the radicle, or embryonic root. The portion of the embryonic axis above where the cotyledons are attached is the epicotyl & consists of the shoot tip with a pair of miniature leaves. The cotyledons of the bean are packed with starch before the seed germinates. They absorbed carbohydrates from the endosperm when the seed developed.
(Campbell & Reece, 2005)

The seeds of some eudicots, such as castor beans, retain their food supply in the endosperm and have cotyledons that are very thin. The cotyledons absorb nutrients from the endosperm & transfer them to the rest of the embryo when the seed germinates.
(Campbell & Reece, 2005)

The embryo of a monocot has a single cotyledon. Members of the grass family, maize & wheat, have a specialized type of cotyledon, a scutellum.
The scutellum is very thin, with a large surface area pressed against the endosperm, from which the scutellum absorbs nutrients during germination. The embryo of a grass seed is enclosed by two sheathes: a coleoptile, which covers the young shoot, & a coleorhiza, which covers the young root.
(Campbell & Reece, 2005)

 While the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and, when mature, aids in their dispersal by wind or animals.
Fertilization triggers hormonal changes that cause the ovary to begin its transformation into a fruit. If a flower has not been pollinated, fruit usually does not develop, & the entire flower withers and falls away. During fruit development, the ovary wall becomes the pericarp, the thickened wall of the fruit. As the ovary grows, the other parts of the flower wither and are shed.
(Campbell & Reece, 2005)

 Most fruits are derived from a single carpel or several fused carpels & are called simple fruits.
Some simple fruits are fleshy, such as a peach, whereas others are dry, such as a pea pod or a nut.
(Campbell & Reece, 2005)

 An aggregate fruit results from a single flower that has more than one separate carpel, each forming a small fruit. These fruitlets are clustered together on a single receptacle, as in a raspberry.
(Campbell & Reece, 2005)

 A multiple fruit develops from an inflorescence, a group of flowers tightly clustered together. When the walls of the many ovaries start to thicken, they fuse together and become incorporated into one fruit, as in a pineapple.
(Campbell & Reece, 2005)

 As a seed matures, it dehydrates and enters a phase referred to as dormancy, a condition of extremely low metabolic rate and suspension of growth and development. Conditions required to break dormancy vary between plant species. Some seeds germinate as soon as they are in a suitable environment. Other seeds remain dormant even if sown in a favorable place until a specific environmental cue causes them to break dormancy.
(Campbell & Reece, 2005)

 Germination of seeds depends on a physical process imbibition, the uptake of water due to the low water potential of the dry seed. Imbibing water causes the seed to expand & rupture its coat. It triggers metabolic changes in the embryo that enable it to resume growth. After hydration, enzymes digest storage materials of the endosperm/cotyledons, & nutrients are transferred to the growing regions of the embryo. The 1 st organ to emerge from the germinating seed is the radicle, the embryonic root. The shoot tip must break through the soil surface.
(Campbell & Reece, 2005)

(Campbell &
Reece, 2005)
 In garden beans & other eudicots, a hook forms in the hypocotyl, & growth pushes the hook above ground. Stimulated by light, the hypocotyl straightens, & raises the cotyledons & epicotyl. The delicate shoot apex & bulky cotyledons are pulled upward rather than being pushed tip, first through the abrasive soil. The epicotyl now spreads its first foliage leaves.
The foliage leaves expand, become green, & begin making food by photosynthesis. The cotyledons shrivel & fall away from the seedling, their food reserves having been exhausted by the germinating embryo.

(Campbell &
Reece, 2005)
 Maize & other grasses, which are monocots, use a different method for breaking ground when they germinate. The coleoptile, the sheath enclosing & protecting the embryonic shoot, pushes upward through the soil & into the air. The shoot tip then grows straight up through the tunnel provided by the tubular coleoptile and eventually breaks out through the coleoptile ′ s tip.