fig. 38.1. perfect flowers have both stamen and carpel- imperfect flowers the stamen and carpel are...

Fig. 38.1

Perfect flowers have both stamen and carpel-

Imperfect flowers the stamen and carpel are on separate flowers

Perfect flowers have both stamen and carpel-

Imperfect flowers the stamen and carpel are on separate flowers

Monoecious plants have both capellate and stamenate flowers

Dioecious is on different plants

Monoecious plants have both capellate and stamenate flowers

Dioecious is on different plants

The four kinds of floral organs are the sepals, petals, stamens, and carpals

Mitosis results in a tube cell and a generative cell

Mitosis results in a tube cell and a generative cell

Central cell

• A microspore divides once by mitosis and produces a generative cell and a tube cell.– The generative cell will eventually form 2 sperm.– The tube cell, enclosing the generative cell,

produces the pollen tube, which delivers sperm to the egg.

– This two-celled structure is encased in a thick, ornate, distinctive, and resistant wall.

– This is a pollen grain, animmature male gametophyte.

Fig. 38.5

• For example, in some species stamens and carpels mature at different times.

• Alternatively, they may be arranged in such a way that it is unlikely that an animal pollinator could transfer pollen from the anthers to the stigma of the same flower.

Fig. 38.6

Self-incompatible genes prevents inbreedingSelf-incompatible genes prevents inbreeding

Recognition of self is due to S-genes

If the S-genes match then there is a biochemical block which is made

RNAses are made by the stigma which destroy the RNA in pollen tubes or may trigger a signal transduction pathway in the stigma (on next slide)

Recognition of self is due to S-genes

If the S-genes match then there is a biochemical block which is made

RNAses are made by the stigma which destroy the RNA in pollen tubes or may trigger a signal transduction pathway in the stigma (on next slide)

2N2N

Pollen are 1NPollen are 1N

Sporophytic self-incompatabilitySporophytic self-incompatability

Receptor Receptor

Kinase triggers a Signal Transduction Pathway

Kinase triggers a Signal Transduction Pathway

Effector proteins activated to block pollen tube

Effector proteins activated to block pollen tube

Double Fertilization ensures that the endosperm will only start storing food when the zygote starts developing into the embryo

Double Fertilization ensures that the endosperm will only start storing food when the zygote starts developing into the embryo

• The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell, and a terminal cell which gives rise to most of the embryo.– The basal cell continues to divide transversely,

producing a thread of cells, the suspensor, which anchors the embryo to its parent.• This passes nutrients to the embryo from the parent.

Fig. 38.10

Animation 38.2.5 Endosperm F.MOV

Endosperm has been absorbed into the cotyledons

Endosperm has been absorbed into the cotyledons

Cotyledons in other plants act to digest and absorb the endosperm

• The seed of a monocot has a single cotyledon.– Members of the grass family, including maize and

wheat, have a specialized 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.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 38.11c

Animation 38.2.7 Seed Germin.MOV

Thickened wall of the fruit

Thickened wall of the fruit

• Fruits are classified into several types– Depending on their developmental origin

Figure 38.9a–c

Simple fruit. A simple fruit develops from a single carpel (or several fused carpels) of one flower (examples: pea, lemon, peanut).

(a) Aggregate fruit. An aggregate fruit develops from many separate carpels of one flower (examples: raspberry, blackberry, strawberry).

(b)

Multiple fruit. A multiple fruit develops from many carpels of many flowers (examples: pineapple, fig).

(c)

Pineapple fruitRaspberry fruit

Pea fruit

Stamen

Carpel(fruitlet)

Stigma

Ovary

Raspberry flower

Eachsegmentdevelopsfrom thecarpel ofone flower

Pineapple inflorescence

Stamen

CarpelsFlower

Ovary

StigmaStamen

Ovule

Pea flower

Seed

Animation 38.2.6 Fruit Devel.MOV

When the seed imbibes water it triggers the embryo to release gibberillic acid

When the seed imbibes water it triggers the embryo to release gibberillic acid

GA will cause Aleurone to secrete amylase which digests the starch in the endosperm

GA will cause Aleurone to secrete amylase which digests the starch in the endosperm

The Radicle comes out first from the seed

The Radicle comes out first from the seed

The Hypocotyl hook emerges first out of the ground- light causes straightening

The Hypocotyl hook emerges first out of the ground- light causes straightening

In peas the Epicotyl hook emerges first out of the ground

In peas the Epicotyl hook emerges first out of the ground

• Corn and other grasses, which are monocots, use yet a different method for breaking ground when they germinate.– The coleoptile pushes upward through the soil and

into the air.– The shoot tip then grows straight up through the

tunnel provided by the tubular coleoptile.


Fig. 38.14c

•The embryo of a grass seed is enclosed by two sheaths, a coleorhiza, which covers the young root, and a coleoptile, which cover the young shoot.

Animation 38.2.8 Seedling Gr.MOV

Vegetative Propagation and Agriculture

• Humans have devised various methods for asexual propagation of angiosperms

Vegetative Reproduction (asexual)

ParentBud

Kalanchoe

Clones from Cuttings

• Many kinds of plants– Are asexually reproduced from plant fragments

called cuttings

Grafting• In a modification of

vegetative reproduction from cuttings– A twig or bud from one plant

can be grafted onto a plant of a closely related species or a different variety of the same species

• Plant biotechnologists have adopted in vitro methods to create and clone novel plants varieties.– Whole plants are cultured from small explants

(small tissue pieces) or even single parenchyma cells, on an artificial medium containing nutrients and hormones.

– Through manipulations of the hormonal balance, the callus that forms can be induced to develop shoots and roots with fully differentiated cells.


Fig. 38.16

Explants or cells from plants can be used to clone whole plants

-this can result in a MONOCULTURE-what are good and bad points about this?

Explants or cells from plants can be used to clone whole plants

-this can result in a MONOCULTURE-what are good and bad points about this?

• One method that researchers use to insert foreign DNA into plant cells is by firing DNA-coated pellets into cultured plant cells.– These projectiles penetrate cell walls and

membranes, introducing foreign DNA into the nuclei of some cells.

– A cell that integrates this DNA into its genome can be cultured to produce a plantlet which can be cloned.

Fig. 38.17

A Transgenic cell can be made by shooting in foreign genes into plant cells

A Transgenic cell can be made by shooting in foreign genes into plant cells

• Another approach combines protoplast fusion with tissue culture to invent new plant varieties.– Protoplasts are plant cells that have had their cell

walls removed enzymatically by cellulases and pectinases.

– It is possible in some cases to fuse two protoplasts from different plant species that would otherwise be incompatible.

– The hybrids can regenerate a wall, be cultured, and produce a hybrid plantlet.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 38.18

• Humans have intervened in the reproduction and genetic makeup of plants for thousands of years.– Neolithic (late Stone Age) humans domesticated

virtually all of our crop species over a relatively short period about 10,000 years ago.• However, even for these plants, genetic modifications began

long before humans started altering crops by artificial selection.

• For example, the wheat groups that we harvest are the result of natural hybridizations between different species of grasses.

1. Neolithic humans created new plant varieties by artificial selection


• Selective breeding by humans has created plants that could not survive for long in the wild.– For example, domesticated maize cannot spread its

seeds naturally.– Humans selected for a larger central axis (“the

cob”), permanent attachment of the maize kernels to the cob, and a permanent protection by tough, overlapping leaf sheaths (“the husk’).


Fig. 38.19

• Maize is a staple in many developing countries.– However, because most varieties are a relative poor

source of protein, a diet of maize must be supplemented with other proteins sources such as beans.

– Forty years ago a mutant maize, known as opaque-2, was discovered with much higher levels of tryptophan and lysine, two essential amino acids, but these traits were closely associated with several undesirable ones.

– It took nearly 20 years for plant breeders, using conventional breeding methods of hybridization and natural selection, to create maize varieties that had higher nutritional value without the undesirable traits.

• Unlike traditional plant breeders, modern plant biotechnologists, using the techniques of genetic engineering, are not limited to transferring genes between closely related species or varieties of the same species.– Instead, genes can be transferred between distantly

related plant species to create transgenic plants, organisms that have been genetically engineered to express a foreign gene from another species.


• Whatever the social and demographic causes of human starvation around the world, increasing food production seems like a humane objective.– Because land and water are the most limiting

resources for food production, the best option will be to increase yields on available lands.

– Based on conservative estimates of population growth, the world’s farmers will have to produce 40% more grain per hectare to feed the human population in 2020.

2. Biotechnology is transforming agriculture


Reducing World Hunger and Malnutrition

• Genetically modified plants– Have the potential of increasing the quality and quantity of food

worldwide

Figure 38.15Ordinary rice

Genetically modified rice

Figure 38.16

• Considerable progress has been made in the development of transgenic plants of cotton, maize, soybeans, sugar beat, and wheat that are tolerant of a number of herbicides.

• Researchers have also engineered transgenic plants with enhanced resistance to disease.– Transgenic papaya,

resistant to ringspot virus, was introduced to Hawaii, thereby saving the papaya industry.


Fig. 38.20

• Many people, including some scientists, are concerned about the unknown risks associated with the release of GM organisms into the environment.– Much of the animosity regarding GM organisms is

political, economic, or ethical in nature, but there are also biological concerns about GM crops.

– The most fundamental debate centers on the extent to which GM organisms are an unknown risk that could potentially cause harm to human health or to the environment.

3. Plant biotechnology has incited much public debate


• One specific concern is that genetic engineering could potentially transfer allergens, molecules to which some humans are allergic, from a gene source to a plant used for food.– So far there is no credible evidence that any GM

plants specifically designed for human consumption have had any adverse effect on human health.

– However, some activists lobby for clear labeling of all foods made wholly or in part from products of GM organisms and for strict regulations against mixing GM foods with non-GM foods at any stage.

– Biotechnology advocates argue that similar demands were not raised when “transgenic” crops were produced by traditional plant breeding techniques.


Effect of Bt toxinInsect larvae and adults feeding on plants which express the bacterial Bt toxin gene stop feeding within 24hr. after ingestion of the toxin, and starve to death within days of feeding.

• There are concerns that growing GM crops might have unforeseen effects of nontarget organisms.

– One recent study indicated that the caterpillars of monarch butterflies responded adversely and even died after consuming milkweed leaves heavily dusted with pollen from transgenic maize that produced Bt toxin.

• The Bt toxin normally is toxic to pests closely related to monarch butterflies.

– In the field, the transgenic pollen appears to be abundant primarily in or very close to the fields.

– Also, the alternative to transgenic maize, spraying chemical insecticides, may be even more harmful to nearby monarch populations.

• Probably the most serious concern that some scientists raise is the possibility that introduced genes may escape from a transgenic crop into related weeds through crop-to-weed hybridization.– This spontaneous hybridization may lead to a

“superweed” which may be more difficult to control.– Strategies to minimize risk include planting a border of

unrelated plants with which the transgenic plants would not hybridize through the spread of transgenic pollen.

– Another possibility is breeding male sterility in transgenic plants.

– Alternatively, the transgenes can be engineered into choloroplasts, which are inherited maternally only.

• The continuing debate about GM organisms in agriculture exemplifies the relationship of science and technology to society.– Technological advances almost always involve

some risk that some unintended outcomes could occur.

– In the case of plant biotechnology, zero risk is unrealistic and probably unattainable.

– Scientists and the public need to assess the possible benefits of transgenic products versus the risks society is willing to take on a case-by-case basis.

– These discussions and decisions should be based on sound scientific information and testing rather than on reflexive fear or blind optimism.

fig. 38.1. perfect flowers have both stamen and carpel- imperfect flowers the stamen and carpel are...

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