Homework to be emailed to valenciabiologyhw@gmail.com
The Brazil nut tree, Bertholletia excels (n = 17), is native to tropical rain forests of South America. It is a hardwood tree that can grow to over 50 meters, is a source of high-quality lumber, and is a favorite nesting site for harpy eagles. As the rainy season ends, tough-walled fruits, each containing 825 seeds (Brazil nuts), fall to the forest floor. About $50 million worth of nuts are harvested each year. Scientists have discovered that the pale yellow, self-incompatible flowers of Brazil nut trees admit only female orchid bees as pollinators.
1 Animals that consume Brazil nuts are deriving nutrition mostly from tissue whose nuclei have how many chromosomes?
2 The agouti (Dasyprocta spp.), a cat-sized rodent, is the only animal with teeth strong enough to crack the hard wall of Brazil nut fruits. It typically eats some of the seeds, buries others, and leaves still others behind inside the fruit, which moisture can now enter. The uneaten seeds may subsequently germinate. Consequently, which terms describe the relationship between the Brazil nut tree and the agouti?
1. parasitic 2. commensalistic 3. symbiotic 4. endosymbiotic 5. mutualistic
3 Entrepreneurs attempted, but failed, to harvest nuts from plantations grown in Southeast Asia. Attempts to grow Brazil nut trees in South American plantations also failed. In both cases, the trees grew vigorously, produced healthy flowers in profusion, but set no fruit. Consequently, what is the likely source of the problem?
4 The agouti is most directly involved with the Brazil nut tree's dispersal
5 The harpy eagle, Harpia harpyja, is the largest, most powerful raptor in the Americas. It nests only in trees taller than 25 meters. It is a "sloth specialist," but will also take agouti. Thus, if these eagles capture too many agoutis from a particular locale, they might contribute to their own demise by
6 Brazil nut trees begin producing fruit at the age of 10 years, reach final height at about 120 years, and can live for over 500 years. A landowner can earn more by felling a Brazil nut tree and selling it for lumber than from several seasons' worth of Brazil nut harvests from the same tree. Thus, it makes greater financial sense in the long run to harvest
7 Native peoples traditionally use Brazil nuts to treat stomach ache, inflammation, hypersensitivity, and hepatitis. Consequently, a scientist should be interested in promoting
8 In the long run, harvesting Brazil nut trees for their lumber is most likely to benefit
9 People who attempted to plant Brazil nuts in hopes of establishing plantations of Brazil nut trees played roles most similar to those of
10 The same bees that pollinate the flowers of the Brazil nut trees pollinate orchids, which are epiphytes (in other words, plants that grow on other plants); however, orchids cannot grow on Brazil nut trees. These observations explain
11 Describe the adaptations of seed plants that have contributed to their success on land
12. Distinguish between pollination and fertilization
13. Compare the size and independence of the gametophytes of bryophytes with those of seed plants
14. Explain how climatic changes with the formation of the supercontinent Pangaea favored the spread of gymnosperms.
15. Define fruit. Explain how fruits may be adapted to disperse seeds
Bryophytes - no roots, leaves or stems, no vascular system, simple
reproduction relying on water, gametophyte (haploid) dominant generation
ferns - first vascular system, rhizomes (horizontal stems), fronds, sporophyte
(diploid) dominant generation
Plant Evolution
Gymnosperms - first leaves (needles), vascular system, stems and roots, naked
seeds
Angiosperms - vascular system more organized, leaves, ability to shed leaves,
seed provided with nutritive tissues, flowers, more sophisticated reproductive
methods
Angiosperms
Flowering, vascular plants
most successful plants
fertilization in flowering plants called double fertilization
2 sperm involved - 1 fertilizes the egg, the other fuses with 2 cells in female
gametophyte to form endosperm
Overview: Feeding the World
Seeds changed the course of plant evolution
Enabling their bearers to become the dominant producers in most terrestrial
ecosystems
The reduced gametophytes of seed plants are protected in ovules and pollen
grains
In addition to seeds, the following are common to all seed plants
Reduced gametophytes
Heterospory
Ovules
Pollen
Advantages of Reduced Gametophytes
The gametophytes of seed plants
Develop within the walls of spores retained within tissues of the parent
sporophyte
Gametophyte/sporophyte relationships
Heterospory: The Rule Among Seed Plants
Seed plants evolved from plants that had megasporangia
Which produce megaspores that give rise to female gametophytes
Seed plants evolved from plants that had microsporangia
Which produce microspores that give rise to male gametophytes
Ovules and Production of Eggs
An ovule consists of
A megasporangium, megaspore, and protective integuments
Pollen and Production of Sperm
Microspores develop into pollen grains
Which contain the male gametophytes of plants
Pollination
Is the transfer of pollen to the part of a seed plant containing the ovules
If a pollen grain germinates
It gives rise to a pollen tube that discharges two sperm into the female
gametophyte within the ovule
Pollen, which can be dispersed by air or animals
Eliminated the water requirement for fertilization
The Evolutionary Advantage of Seeds
A seed
Develops from the whole ovule
Is a sporophyte embryo, along with its food supply, packaged in a protective
coat
: Gymnosperms bear “naked” seeds, typically on cones
Among the gymnosperms are many well-known conifers
Or cone-bearing trees, including pine, fir, and redwood
The gymnosperms include four plant phyla
Cycadophyta
Gingkophyta
Gnetophyta
Coniferophyta
Exploring Gymnosperm Diversity
Exploring Gymnosperm Diversity
Because of both its extreme rarity and its splendid appearance, Encephalartos
woodii is one of the most sought-after plants in the world. Only one specimen
was ever discovered in habitat—the male multi-stemmed clump found by Medley Wood
in the Ngoye Forest, Zululand, in 1895—although unsubstantiated rumors of a
second male plant have been heard.
Why there were not more plants is not clear; one theory is that the species was
depleted through its use in Zulu ceremonial rites, while some authorities
suggest that the plant might be a natural hybrid and perhaps no other specimen
of its kind did ever exist.
Nevertheless, E. woodii is now regarded as extinct in nature.
Fortunately, E. woodii produces offsets quite readily and careful vegetative
propagation has resulted in a fair number (500?) of plants being established in
major botanical gardens and private collections throughout the world. Since all
these plants are male, it is impossible to propagate the species from seed.
The first approach is being adopted by Cynthia Giddy* at her Umlaas Road nursery
and has been described by D.C. Speirs. Pollen from male cones of the existing E.
woodii plants is used to fertilize E. natalensis, the species which seems to be
most closely related. Females from this hybrid generation (F1, 5O% E. woodii)
are back-crossed with more E. woodii pollen to give another generation a little
closer to pure E. woodii (F2, 75% E. woodii).
The process is repeated until an almost pure population is established--e.g.,
the F5 generation would be 97% E. woodii. The disadvantage, of course, lies in
the length of time from one generation to another; assuming 12 years for each
batch to come to maturity, the 5-generation process takes 60 years.
A second plan of action follows from the rather unusual, but now well-documented
evidence that sex changes can and do occur in cycads……
Gymnosperm Evolution
Fossil evidence reveals that by the late Devonian
Some plants, called progymnosperms, had begun to acquire some adaptations that
characterize seed plants
Gymnosperms appear early in the fossil record
And dominated the Mesozoic terrestrial ecosystems
Living seed plants
Can be divided into two groups: gymnosperms and angiosperms
Plants
Three life cycle modifications contributed to seed plant success:
1. Gametophytes became reduced and were retained in the moist reproductive
tissue of the sporophyte generation (not independent).
Plants
2. Pollination evolved, so plants were no longer tied to water for
fertilization.
3. The evolution of the seed.
· Zygote develops into an embryo packaged with a food supply within a protective
seed coat.
Seeds replace spores as main means of dispersal.
Gymnosperms began to dominate landscapes as climates became drier at the end of
the Paleozoic era
Plants
Gymnosperms appear in the fossil record much earlier than flowering plants, and
they:
· Lack enclosed chambers in which seeds develop.
Are grouped into four divisions: Cycadophpyta, Ginkgophyta, Gnetophyta and
Coniferophyta.
Division Coniferophyta (Conifers)
Division Coniferophyta is the largest division of gymnosperms:
Most are evergreens and include pines, firs, spruces, larches, yews, junipers,
cedars, cypresses, and redwoods
Includes some of the tallest (redwoods and some eucalyptus); largest (giant
sequoias); and oldest (bristle cone pine) living organisms.
•Most lumber and paper pulp is from conifer wood.
Needle-shaped conifer leaves are adapted to dry conditions
· Thick cuticle covers the leaf.
· Stomata are in pits, reducing water loss.
Despite the shape, needles are megaphylls, as are leaves of all seed plants.
Plants
. The Life History of a Pine
The life cycle of pine, a representative conifer, is characterized by the
following:
The multicellular sporophyte is the most conspicuous stage; the pine tree is a
sporophyte, with its sporangia located on cones.
Plants
The multicellular gametophyte
generation is reduced and develops from haploid spores that are retained within
sporangia.
The male gametophyte is the pollen grain; note that there is no antheridium.
The female gametophyte consists of multicellular nutritive tissue and an
archegonium that develops within an ovule.
Conifer life cycles are heterosporous; male and female gametophytes develop from
different types of spores produced by separate cones.
· Trees of most pine species bear both
pollen cones and ovulate cones, which develop on different branches.
Plants
Pollen cones have microsporangia; cells in these sporangia undergo meiosis
producing haploid microspores, small spores that develop into pollen grains -
the male gametophytes.
Ovulate cones have megasporangia; cells in these sporangia undergo meiosis
producing large megaspores that develop into the female gametophyte. Each ovule
initially includes a sporangium (nucellus) enclosed in protective integuments
with a single opening, the micropyle.
Plants
It takes nearly three years to complete the pine life cycle, which progresses
through a complicated series of events to produce mature seeds.
Windblown pollen falls onto the ovulate cone and is drawn into the ovule through
the micropyle.
The pollen grain germinates in the ovule, forming a pollen tube that begins to
digest its way through the nucellus.
A megaspore mother cell in the nucellus undergoes
meiosis producing four haploid megaspores, one of which will survive; it divides
repeatedly by mitosis producing the immature female gametophyte.
Two or three archegonia, each with an egg, then develop
within the multicellular gametophyte.
More than a year after pollination, the eggs are ready to be fertilized; two
sperm cells have developed and the pollen tube has grown through the nucellus to
the female gametophyte.
Fertilization occurs when one of the sperm
nuclei unites with the egg nucleus. All eggs in an ovule may be fertilized, but
usually only one zygote develops into an embryo.
The pine embryo, or new sporophyte, has a rudimentary root and several embryonic
leaves. It is embedded in the female gametophyte, which nourishes the embryo
until it is capable of photosynthesis. The ovule has developed into a pine seed,
which consists of an embryo (2n), its food source (n), and a surrounding seed
coat (2n) derived from the parent tree.
Scales of the ovulate cone separate, and the winged seeds are carried by the
wind to new locations. Note, that with the seed plants, the seed has replaced
the spore as the mode of dispersal.
A seed that lands in a habitable place germinates, its embryo emerging as a pine
seedling.
Plants
The History of Gymnosperms
Gymnosperms descended from Devonian progymnosperms.
· Adaptive radiation during the Carboniferous and Permian
periods led to today's divisions.
During the Permian, Earth became warmer and drier; therefore, lycopods,
horsetails and ferns (previously dominant) were largely replaced by conifers and
their relatives, the cycads
This large change marks the end of the Paleozoic era and the beginning of the
Mesozoic era.
A Closer Look at the Life Cycle of a Pine
Key features of the gymnosperm life cycle include
Dominance of the sporophyte generation, the pine tree
The development of seeds from fertilized ovules
The role of pollen in transferring sperm to ovules
: The reproductive adaptations of angiosperms include flowers and fruits
Angiosperms
Are commonly known as flowering plants
Are seed plants that produce the reproductive structures called flowers and
fruits
Are the most widespread and diverse of all plants
Characteristics of Angiosperms
The key adaptations in the evolution of angiosperms
Are flowers and fruits
Flowers
The flower
Is an angiosperm structure specialized for sexual reproduction
A flower is a specialized shoot with modified leaves
Sepals, which enclose the flower
Petals, which are brightly colored and attract pollinators
Stamens, which produce pollen
Carpels, which produce ovules
Fruits
Fruits
Typically consist of a mature ovary
Can be carried by wind, water, or animals to new locations, enhancing seed
dispersal
The Angiosperm Life Cycle
In the angiosperm life cycle
Double fertilization occurs when a pollen tube discharges two sperm into the
female gametophyte within an ovule
One sperm fertilizes the egg, while the other combines with two nuclei in the
center cell of the female gametophyte and initiates development of food-storing
endosperm
The endosperm
Nourishes the developing embryo
Angiosperm Evolution
Clarifying the origin and diversification of angiosperms
Poses fascinating challenges to evolutionary biologists
Angiosperms originated at least 140 million years ago
And during the late Mesozoic, the major branches of the clade diverged from
their common ancestor
Fossil Angiosperms
Primitive fossils of 125-million-year-old angiosperms
Display both derived and primitive traits
An “Evo-Devo” Hypothesis of Flower Origins
In hypothesizing how pollen-producing and ovule-producing structures were
combined into a single flower
Scientist Michael Frohlich proposed that the ancestor of angiosperms had
separate pollen-producing and ovule-producing structures
Angiosperm Diversity
The two main groups of angiosperms
Are monocots and eudicots
Basal angiosperms
Are less derived and include the flowering plants belonging to the oldest
lineages
Magnoliids
Share some traits with basal angiosperms but are more closely related to
monocots and eudicots
Exploring Angiosperm Diversity
Evolutionary Links Between Angiosperms and Animals
Pollination of flowers by animals and transport of seeds by animals
Are two important relationships in terrestrial ecosystems
Evolutionary Links Between Angiosperms and Animals
: Human welfare depends greatly on seed plants
No group is more important to human survival than seed plants
Products from Seed Plants
Humans depend on seed plants for
Food
Wood
Many medicines
Threats to Plant Diversity
Destruction of habitat
Is causing extinction of many plant species and the animal species they support
Fruits
Typically consist of a mature ovary
Can be carried by wind, water, or animals to new locations, enhancing seed
dispersal
The Angiosperm Life Cycle
In the angiosperm life cycle
Double fertilization occurs when a pollen tube discharges two sperm into the
female gametophyte within an ovule
One sperm fertilizes the egg, while the other combines with two nuclei in the
center cell of the female gametophyte and initiates development of food-storing
endosperm
The endosperm
Nourishes the developing embryo
Overview: To Seed or Not to Seed
The parasitic plant Rafflesia arnoldii
Produces enormous flowers that can produce up to 4 million seeds
: Pollination enables gametes to come together within a flower
In angiosperms, the dominant sporophyte
Produces spores that develop within flowers into male gametophytes (pollen
grains)
Produces female gametophytes (embryo sacs)
An overview of angiosperm reproduction
Flower Structure
Flowers
Are the reproductive shoots of the angiosperm sporophyte
Are composed of four floral organs: sepals, petals, stamens, and carpels
Many variations in floral structure
Have evolved during the 140 million years of angiosperm history
Gametophyte Development and Pollination
In angiosperms
Pollination is the transfer of pollen from an anther to a stigma
If pollination is successful, a pollen grain produces a structure called a
pollen tube, which grows down into the ovary and discharges sperm near the
embryo sac
Mechanisms That Prevent Self-Fertilization
Many angiosperms
Have mechanisms that make it difficult or impossible for a flower to fertilize
itself
The most common anti-selfing mechanism in flowering plants
Is known as self-incompatibility, the ability of a plant to reject its own
pollen
Researchers are unraveling the molecular mechanisms that are involved in
self-incompatibility
Some plants
Reject pollen that has an S-gene matching an allele in the stigma cells
Recognition of self pollen
Triggers a signal transduction pathway leading to a block in growth of a pollen
tube
: After fertilization, ovules develop into seeds and ovaries into fruits
Double Fertilization
After landing on a receptive stigma
A pollen grain germinates and produces a pollen tube that extends down between
the cells of the style toward the ovary
The pollen tube
Then discharges two sperm into the embryo sac
In double fertilization
One sperm fertilizes the egg
The other sperm combines with the polar nuclei, giving rise to the food-storing
endosperm
From Ovule to Seed
After double fertilization
Each ovule develops into a seed
The ovary develops into a fruit enclosing the seed(s)
Endosperm Development
Endosperm development
Usually precedes embryo development
In most monocots and some eudicots
The endosperm stores nutrients that can be used by the seedling after
germination
In other eudicots
The food reserves of the endosperm are completely exported to the cotyledons
Embryo Development
The first mitotic division of the zygote is transverse
Splitting the fertilized egg into a basal cell and a terminal cell
Structure of the Mature Seed
The embryo and its food supply
Are enclosed by a hard, protective seed coat
In a common garden bean, a eudicot
The embryo consists of the hypocotyl, radicle, and thick cotyledons
The seeds of other eudicots, such as castor beans
Have similar structures, but thin cotyledons
The embryo of a monocot
Has a single cotyledon, a coleoptile, and a coleorhiza
From Ovary to Fruit
A fruit
Develops from the ovary
Protects the enclosed seeds
Aids in the dispersal of seeds by wind or animals
Fruits are classified into several types
Depending on their developmental origin
Couroupita guianensis
Cannon Ball Tree
The amazingly complex flower of the Cannonball Tree is also heavenly scented - a
cross between a fine expensive perfume and a wonderful flower scent
Fruits are classified into several types
Depending on their developmental origin
Fruits are classified into several types
Depending on their developmental origin
Seed Germination
As a seed matures
It dehydrates and enters a phase referred to as dormancy
Seed Dormancy: Adaptation for Tough Times
Seed dormancy
Increases the chances that germination will occur at a time and place most
advantageous to the seedling
The breaking of seed dormancy
Often requires environmental cues, such as temperature or lighting cues
From Seed to Seedling
Germination of seeds depends on the physical process called imbibition
The uptake of water due to low water potential of the dry seed
The radicle
Is the first organ to emerge from the germinating seed
In many eudicots
A hook forms in the hypocotyl, and growth pushes the hook above ground
Monocots
Use a different method for breaking ground when they germinate
The coleoptile
Pushes upward through the soil and into the air
Many flowering plants clone themselves by asexual reproduction
Many angiosperm species
Reproduce both asexually and sexually
Sexual reproduction
Generates the genetic variation that makes evolutionary adaptation possible
Asexual reproduction in plants
Is called vegetative reproduction
Mechanisms of Asexual Reproduction
Fragmentation
Is the separation of a parent plant into parts that develop into whole plants
Is one of the most common modes of asexual reproduction
In some species
The root system of a single parent gives rise to many adventitious shoots that
become separate shoot systems
Vegetative Propagation and Agriculture
Humans have devised various methods for asexual propagation of angiosperms
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
Test-Tube Cloning and Related Techniques
Plant biologists have adopted in vitro methods
To create and clone novel plant varieties
In a process called protoplast fusion
Researchers fuse protoplasts, plant cells with their cell walls removed, to
create hybrid plants
Plant biotechnology is transforming agriculture
Plant biotechnology has two meanings
It refers to innovations in the use of plants to make products of use to humans
It refers to the use of genetically modified (GM) organisms in agriculture and
industry
Modifications in reproduction were key adaptations enabling plants to spread
into a variety of terrestrial habitats.
Water has been replaced by wind and animals as a means for spreading gametes.
· Embryos are protected in seeds.
Vegetative reproduction is an asexual mechanism for propagation in many
environments.
Flowers
The angiosperm (flowering plant) life cycle includes alternation of generations
during which multicellular haploid gametophyte generations alternate with
diploid sporophyte generations
Flowers
The angiosperm (flowering plant) life cycle includes alternation of generations
during which multicellular haploid gametophyte generations alternate with
diploid sporophyte generations
Flowers
‘Gametophytes produce gametes (sperm and egg) by mitosis. The gametes fuse to
form a zygote which develops into a multicellular sporophyte.
Flowers
The sporophyte is dominant in the angiosperm life cycle with the gametophyte
stages being reduced and totally dependent on the sporophyte.
Flowers
Flowers are the reproductive structure of angiosperm sporophytes.
Evolved from compressed shoots with four whorls of modified leaves separated by
very short internodes.
The four sets of modified leaves are the: sepals, petals, stamens, and carpels.
Flowers
Stamens and carpels contain the sporangia and are the reproductive parts of the
flower.
Female gametophytes develop in carpel sporangia as embryo sacs which contain the
eggs. This occurs inside the ovules which are at the base of the carpel and
surrounded by ovaries.
Flowers
‘Male gametophytes develop in the stamen sporangia as pollen grains. These form
at the stamen tips within chambers of the anthers.
Flowers
Pollination occurs when wind- or animal-born pollen released from anthers lands
on the stigma at the tip of a carpel.
· A pollen tube grows from the pollen
grain, down the carpel, into the embryo sac.
Sperm are discharged resulting in fertilization of the eggs.
Flowers
· The zygote will develop into an embryo; as the embryo grows, the
ovule surrounding it develops into a seed.
While seed formation is taking place, the entire ovary is developing into a
fruit which will contain one or more seeds.
Flowers
‘Seeds are dispersed from the source plant when fruits are moved about by the
wind or animals.
Seeds deposited in soil of the proper conditions (moisture, nutrients) will
germinate.
Flowers
The embryo starts growing and develops into a new sporophyte.
After flowers are produced by the sporophyte, a new generation of gametophytes
develop and the life cycle continues.
Flowers
More About Flowers
Several variations on the basic flower structure have evolved during the
angiosperm evolutionary history.
Complete flower = A flower with sepals, petals, stamens and carpels.
Incomplete flower = A flower that is missing one or more of the parts listed for
a complete flower (e.g. most grasses do not have petals on their flowers).
FlowersPerfect flower = A flower having both stamens and carpels (may be
incomplete by lacking either sepals or petals).
Imperfect flower = A flower that is either staminate (having stamens but no
carpels) or carpellate (having carpels but no stamens) - a unisex flower.
FlowersMonoecious = Plants having both staminate flowers and carpellate flowers
on the same individual plant.
Dioecious = Plants having staminate flowers and carpellate flowers on separate
individual plants of the species.
Flowers
Development
Pollen grain = The immature male gametophyte that develops within the anthers of
stamens in an angiosperm.
Extremely durable; their tough coats are resistant to biodegradation.
Fossilized pollen has provided many important evolutionary clues.
Flowers
· Formation of a pollen grain is as follows:
Within the sporangial chamber of an anther, diploid microsporocytes undergo
meiosis toform four haploid microspores.
The haploid microspore nucleus undergoes mitotic division to give rise to a
generative cell and a tube cell.
Flowers
The wall of the microspore then thickens and becomes sculptured into a
speciesspecific pattern.
These two cells and the thickened wall are the pollen grain, an immature
male gametophyte.
Flowers
Ovule Development
Ovule = Structure which forms within the chambers of the plant ovary and
contains the female sporangium.
Flowers
The female gametophyte is the embryo sac, and it develops as follows:
A megasporocyte in the sporangium of each ovule grows and goes through meiosis
to form 4 haploid megaspores (only one usually survives).
Flowers
The remaining megaspore grows and its nucleus undergoes 3 mitotic divisions,
forming 1 large cell with 8 haploid nuclei.
Membranes partition this into a multicellular embryo sac
Flowers
Within the embryo sac:
· The egg cell is located at one end and is flanked by two other cells
(synergids).
· At the opposite end are 3 antipodal cells.
· The other 2 nuclei (polar nuclei) share the cytoplasm of the large
central cell.
Flowers
At the end containing the egg is the micropyle (an opening through the
integuments surrounding the embryo sac).
Pollination brings female and male gametophytes together
Flowers
Pollination = The placement of pollen onto the stigma of a carpel.
· Some plants use wind to disperse pollen.
· Other plants interact with animals that transfer pollen directly
between flowers.
Some plants self-pollinate, but most cross-pollinate.
Most monoecious angiosperms have mechanisms to prevent self-pollination. These
mechanisms thus contribute to genetic variation in the species by ensuring sperm
and eggs are from different plants.
· The stamens and carpels mature at
different times in some species.
· Structural arrangement of the flower in
many species pollinated by animals reduces the chance that pollinators will
transfer pollen from anthers to the stigma of the same flower.
FlowersOther species are self-incompatible. If a pollen grain lands on the
stigma of the same flower, a biochemical block prevents the pollen grain from
developing and fertilizing the egg.
FlowersSelf-Incompatibility = The rejection of pollen from the same, or closely
related, plant by the stigma.
Self-incompatibility is a single-gene-based mechanism.
The S-locus is responsible for this reaction.
Many alleles for the S-locus are found in a plant population's gene pool.
Flowers· A pollen grain that lands on a stigma with matching alleles at
the S-locus is selfincompatible.
The pollen grain will either not adhere strongly to the stigma or the pollen
tube will not develop and invade the ovary.
= This prevents self-fertilization and fertilization between plants with a
common S-locus (usually closely related plants).
Flowers
‘Double Fertilization
When a compatible pollen grain (different S-locus alleles) lands on a stigma of
an angiosperm, double fertilization occurs.
Double fertilization = The union of two sperm cells with two cells of the embryo
sac.
Flowers
After adhering to a stigma, the pollen grain
germinates and extends a pollen tube between the cells of the style toward the
ovary.
The generative cell divides (mitosis) to
form two sperm. (A pollen grain with a tube enclosing two sperm = mature male
gametophyte.)
FlowersDirected by a chemical attractant (usually calcium), the tip of the
pollen tube enters through the micropyle and discharges its two sperm nuclei
into the embryo sac.
· One sperm unites with the egg to form the
zygote.
FlowersThe other sperm combines with the two polar nuclei to form a 3N nucleus
in the large central cell of the embryo sac. = This central cell will give rise
to the endosperm which is a food storing tissue.
After double fertilization is completed, each ovule will develop into a seed and
the ovary will develop into a fruit surrounding the seed(s).
Flowers‘The ovule develops into a seed containing a sporophyte embryo and a
supply of nutrients
A. Endosperm Development
Endosperm development begins before embryo development.
The triploid nucleus divides to form a milky, multinucleate "supercell" after
double fertilization.
Flowers
‘· This endosperm undergoes cytokinesis to
form membranes and cell walls between the nuclei, thus, becoming multicellular.
Endosperm is rich in nutrients, which it provides to the developing embryo.
The endosperm in most monocots stocks nutrients which are available to the
seedling after germination.
Flowers
‘In many dicots, food reserves of the endosperm are exported to the cotyledons,
thus mature seeds have no endosperm.
Flowers
‘Embryo Development (Embryogenesis)
During embryogenesis: ·
The zygote's first mitotic division is transverse, creating a larger
basal cell and a smaller terminal cell.
The basal cell divides transversely to form the suspensor, which anchors the
embryo and transfers nutrients to it from the parent plant.
The terminal cell divides several time to form a spherical proembryo attached to
the suspensor.
Cotyledons appear as bumps on the proembryo and the embryo elongates. = The
apical meristem of the embryonic shoot is located between the cotyledons.
Flowers
Where the suspensor (the opposite end of the axis) attaches is the apex of the
embryonic root with its meristem.
= The basal cell gives rise to part of the root meristem in some species.
After germination, the apical meristems at the root and shoot tips will sustain
primary growth.
Flowers
‘= The embryo also contains protoderm, ground meristem and procambium.
· Two features of plant form are established during embryogenesis. = The
root-shoot axis with meristems at opposite ends.
Flowers
‘A radial pattern of protoderm, ground meristem, and procambrium ready to
produce the dermal, ground, and vascular tissue systems.
Flowers
‘Structure of the Mature Seed
In mature seeds, the embryo is quiescent until germination.
· The seed dehydrates until its water content is only 5-15% by
weight.
· The embryo is surrounded by endosperm, enlarged cotyledons, or both.
The seed coat is formed from the integuments of the ovule.
Flowers
Below the cotyledon attachment point, the embryonic axis is termed the
hypocotyl, which terminates in the radicle, or embryonic root.
Above the cotyledons, the embryonic axis is termed the epicotyl, which
terminates in the plumule (shoot tip with a pair of tiny leaves).
Flowers
Fleshy cotyledons are present in some dicots before germination due to their
absorption of nutrients from the endosperm.
In other dicots, thin cotyledons are found and nutrient absorption and transfer
occurs only after germination.
Flowers
‘A monocot seed has a single cotyledon called the scutellum.
· The scutellum has a large surface area and absorbs nutrients
from the endosperm during germination.
The embryo is enclosed in a sheath comprised of the coleorhiza (covers the root)
and the coleoptile (covers the shoot).
Flowers
Evolutionary adaptations in the process of germination increase the probability
that seedlings will survive
Seed germination represents the continuation of growth and development which was
interrupted when the embryo became quiescent at seed maturation.
Flowers
· Some seeds germinate as soon as they reach a suitable
environment. Other seeds require a specific environmental cue before they will
break dormancy.
Flowers
‘Seed Dormancy
The evolution of the seed was an important adaptation by plants to living in
terrestrial habitats.
· The environmental conditions in terrestrial habitats fluctuate more often
than conditions in aquatic habitats.
Flowers
‘Seed dormancy prevents germination when conditions for seedling growth are
unfavorable.
It increases the chance that germination will occur at a time and place most
advantageous to the success of the seedling.
Flowers
‘Conditions for breaking dormancy vary depending on the type of environment the
plant inhabits.
· Seeds of desert plants may not germinate unless there has been heavy rainfall
(not after a light shower).
· In chaparral regions where brushfires are common, seeds may not germinate
unless exposed to intense heat, after a fire has cleared away older, competing
vegetation.
Flowers
‘Other seeds may require exposure to cold, sunlight or passage through an
animal's digestive system before germination will occur.
Dormant seeds may remain viable for a few days to a few decades (most are
viable for at least a year or two).
Flowers
‘This provides a pool of ungerminated seeds in the soil which is one reason
vegetation appears so rapidly after environmental disruptions.
Flowers
‘. From Seed to Seedling
The first step in seed germination in many plants is imbibition (absorption of
water).
Hydration causes the seed to swell and
rupture the seed coat.
· Hydration also triggers metabolic changes in the
embryo that cause it to resume growth.
Flowers
Storage materials of the endosperm or cotyledons are digested by
enzymes and the nutrients transferred to the growing regions of the embryo.
For example, the embryo of a cereal grain releases a hormone (a gibberellin) as
a messenger to the aleurone (outer layer of endosperm) to initiate production of
Flowers
‘(Xamylase and other enzymes that digest starch stored in the endosperm
The radicle (embryonic root) then emerges from the seed.
The next step in the change from a seed to a seedling is the shoot tip breaking
through the soil surface.
In many dicots, a hook forms in the hypocotyl
Flowers
‘=> Growth pushes the hypocotyl above ground.
· Light stimulates the hypocotyl to straighten, raising
the cotyledons and epicotyl.
The epicotyl then spreads the first leaves which become green and begin
photosynthesis.
Flowers
‘Germination may follow different methods depending on the plant species.
In peas, a hook forms in the epicotyl and the shoot tip is lifted by elongation
of the epicotyl and straightening of the hook.
= The cotyledons remain in the ground.
Flowers
‘In monocots, the coleoptile pushes through the soil and the shoot tip grows up
through the tunnel of the tubular coleoptile.
Only a small fraction of the seedlings will survive to the adult plant stage.
· Large numbers of seeds and fruits are produced to compensate for this
loss.
Flowers
‘This utilizes a large proportion of the plant's available energy.
Introduction to Pharmacognosy
A brief history of natural products in medicine
Value of natural drug products
Production of natural drug products
The role of natural products in drug discovery
General principles of botany: morphology and systematics
I. The history of natural products in medicine
A great proportion of the natural products used as drugs
The study of drugs used by traditional healers is an important object of
pharmacognostical research
Sumerians and Akkadians (3rd millennium BC)
Egyptians (Ebers papyrus, 1550 BC)
Authors of antiquity
Hippocrates (460-377 BC)
“The Father of Medicine”
Dioscorides (40-80 AD)
“De Materia Medica” (600 medicinal plants)
The Islamic era
Ibn Altabari (770-850)
” ÝÑÏæÓ ÇáÍßãå“
Ibn Sina (980-1037)
”ÇáÞÇäæä Ýí ÇáØÈ“
Ibn Albitar (1148-1197)
”ÇáÌÇãÚ áãÝÑÏÇÊ ÇáÃÏæíÉ æÇáÃÛÐíÉ“
The era of European exploration overseas (16th and 17th century)
The 18th century, Pharmacognosy
Johann Adam (1759-1809)
Linnaeus (naming and classifying plants)
At the end of the 18th century, crude drugs were still being used as powders,
simple extracts, or tinctures
The era of pure compounds
(In 1803, a new era in the history of medicine)
Isolation of morphine from opium
Strychnine (1817)
Quinine and caffeine (1820)
Nicotine (1828)
Atropine (1833)
Cocaine (1855)
In the 19th century, the chemical structures of many of the isolated compounds
were determined
In the 20th century, the discovery of important drugs from the animal kingdom,
particularly hormones and vitamins.
microorganisms have become a very important source of drugs
Definitions
Pharmacognosy:
It is the science of biogenic or nature-derived pharmaceuticals and poisons
Crude drugs:
It is used for those natural products such as plants or part of plants, extracts
and exudates which are not pure compounds
Ethnobotany:
It is a broad term referring to the study of plants by humans
Ethnomedicine:
It refers to the use of plants by humans as medicine
Traditional medicine:
It is the sum total of all non-mainstream medical practices, usually excluding
so called “western” medicine
Natural products: they can be
Entire organism (plant, animal, organism)
Part of an organism (a leaf or flower of a plant, an isolated gland or other
organ of an animal)
An extract or an exudate of an organism
Isolated pure compounds
Types of drugs derived from plants
Herbal drugs, derived from specific parts of a medicinal plant
Compounds isolated from nature
Nutraceuticals, or “functional foods”
II. Value of natural products
Compounds from natural sources play four significant roles in modern medicine:
They provide a number of extremely useful drugs that are difficult, if not
impossible, to produce commercially by synthetic means
Natural sources also supply basic compounds that may be modified slightly to
render them more effective or less toxic
3. Their utility as prototypes or models for synthetic drugs possessing
physiologic activities similar to the originals
4. Some natural products contain compounds that demonstrate little or no
activity themselves but which can be modified by chemical or biological methods
to produce potent drugs not easily obtained by other methods
Baccatin III ® Taxol
III. Production of natural drug products
Collection (wild)
Cultivation (commercial), collection, harvesting, drying, garbling, packaging,
storage and preservation e.g. ginseng, ginkgo, peppermint
Fermentation (Recombinant DNA technology or Genetically engineered drugs)
Cell-culture techniques
Microbial transformation
Biologics (prepared from the blood of animals)
IV. The role of natural products in drug discovery
Combinatorial chemistry
High-throughput screening of natural products
Combinatorial biosynthesis
Ethnopharmacology
V. General principles of botany: morphology and systematics
How to define a pharmaceutical plant-derived drug from the botanical point of
view ?
a botanical drug is a product that is either:
Derived from a plant and transformed into a drug by drying certain plant parts,
or sometimes the whole plant, or
Obtained from a plant, but no longer retains the structure of the plant or its
organs and contains a complex mixture of biogenic compounds (e.g. fatty and
essential oils, gums, resins, balms)
isolated pure natural products are thus not “botanical drugs”, but rather
chemically defined drugs derived from nature.
the following plant organs are the most important, with the Latin name that is
used, for example in international trade, in parentheses:
Aerial parts or herb (herba)
Leaf (folia)
Flower (flos)
Fruit (fructus)
Bark (cortex)
Root (radix)
Rhizome (rhizoma)
Bulb (bulbus)
The large majority of botanical drugs in current use are derived from leaves or
aerial parts.
A plant-derived drug should be defined not only in terms of the species from
which it is obtained but also the plant part that is used to produce the dried
product. Thus, a drug is considered to be adulterated if the wrong plant parts
are included (e.g. aerial parts instead of leaves)
Taxonomy
It is the science of naming organisms and their correct integration into the
existing system of nomenclature
The names of species are given in binomial form: the first part of the name
indicates the wider taxonomic group, the genus; the second part of the name is
the species.
Papaver somniferum L.
Species: somniferum, here meaning ‘sleep- producing’
Genus: Papaver (a group of species, in
this case poppies, which are
closely related)
Family: Papaveraceae (a group of genera sharing certain traits)
L.: indicates the botanist who provided the first scientific description of the
species and who assigned the botanical name
Morphology of higher plants
1. Flower
It is the essential reproductive organ of a plant.
For an inexperienced observer, two characteristics of a flower are particularly
noteworthy: the size and the color
Although the flowers are of great botanical importance, they are only a minor
source of drugs used in phytotherapy or pharmacy e.g. chamomile, Matricaria
recutita L. (Asteraceae )
2. Fruit and seed
The lower plants, such as algae, mosses and ferns, do not produce seeds
Gymnosperm and Angiosperm
Gymnosperm: they are characterized by seeds that are not covered by a secondary
outer protective layer, but only by the testa – the seed’s outer layer
Angiosperm: the seeds are covered with a specialized organ (the carpels) which
in turn develop into the pericarp.
Drugs from the fruit thus have to be derived from an angiosperm species
Fruits and seeds have yielded important phytotherapeutic products, including:
Fruit
Caraway, Carum carvi L. (Umbelliferae)
Seed
(white) mustard, Sinapis alba L. (Brassicaceae)
3. Leaves
The function of the leaves, as collectors of the sun’s energy and its
assimilation, results in their typical general anatomy with a petiole (stem) and
a lamina (blade)
A key characteristic of a species is the way in which the leaves are arranged on
the stem, they may be:
Alternate
Distichous
Opposte
Decussate
Whorled
The form and size of leaves are essential characteristics e.g. oval, oblong,
obovate, rounded, linear, lanceolate, elliptic, spatulate, cordate, hastate or
tendril
The margin of the leaf is another characteristic feature e.g. entire, serrate,
dentate, sinuate, ciliate or spinose
Numerous drugs contain leaf material as the main component. e.g.
Deadly nightshade, Atropa belladonna L. (Solanaceae)
4. Bark
The bark as an outer protective layer frequently accumulates biologically active
substances e.g.
Red cinchona, Cinchona succirubra L.
(Rubiaceae)
No stem-derived drug is currently of major importance
5. Rhizome and root drugs
Underground organs of only a few species have yielded pharmaceutically important
drugs e.g.
Sarsaparilla, Smilax regelii (Smilacaceae)
Korean ginseng, Panax ginseng (Araliaceae)
6. The bulbs and exudates
Garlic, Allium sativum L. (Liliaceae)
Aloe vera L. (Asphodelaceae)
Medicinal Chemistry
Urgent need to study medicinal plants
To rescue knowledge in imminent danger of being lost
Inventory by WHO found 20,000 plant species in use for medicine in 90 countries
Only 250 of those species are commonly used or have been checked for main active
chemical compounds
Urgent need to study medicinal plants
The utility of plants in current therapy
There has been a rush to develop synthetic medicines based on plant medicines,
but often the synthetic medicines don’t work as well as the original plant
medicines.
For example – quinine and malaria
Efficacy of Quinine
Quinine is traditional and effective preventative of malaria
Synthetic preventatives such as chloroquine, maloprim, and fansidar have largely
replaced the use of quinine
Many strains of Plasmodium have developed resistances to the synthetics and the
synthetics are more toxic. It is recommended that people do not take fansidar
for more than 3 months due to potential liver damage.
Malaria Cycle
Anopheles freeborni mosquito – intermediate host and vector for Plasmodium sp.
Historical distribution of Malaria
Red areas show countries with malaria today
One of the sources of Quinine – Cinchona succirubra
Cinchona pubescens
Timeline of Quinine Use
1633, a Jesuit priest named Father Calancha described how to use quinine bark to
cure fevers
1645 Father Bartolome Tafur took some bark to Rome and many of the clergy used
it
Cardinal John de Lugo wrote a pamphlet to be distributed with the bark - use of
the bark became so widespread that in the papal conclave of 1655 no one died of
malaria
1654 – English aware of use of quinine bark
1735, a French botanist named Joseph de Jussieu journeyed to South America and
found and described the tree that is the source of the bark - he sent samples to
Sweden where in 1739, Carl Linneaus named the tree genus Cinchona
Timeline of Quinine Use
20 to 40 species of Cinchona - the species are very hard to tell apart and the
species will hybridize, so the exact number of species is unknown – mostly
understorey trees
1820 the French chemists Joseph Pelletier and Joseph Caventou isolated the
alkaloid quinine from the bark and identified it was the active ingredient in
Peruvian bark
1861, an Australian named Charles Ledger obtained seeds from an Aymara Indian
named Manuel Incra
by 1930, the Dutch orchards in Java produced 22 million pounds of quinine, 97%
of the world’s market
Chemical structure of quinine
Properties of Quinine
Quinine itself is an odorless white powder with an extremely bitter taste
It can be used to treat cardiac arrhythmias as well as malaria - it is also used
as a flavoring agent
Quinine prevents malaria by suppressing reproduction of the Plasmodium and also
helps prevent some of the fevers and pain associated with malaria
Quinine fluoresces under UV light
Raymond Fosberg in the
field in 1948
Cinchona bark drying in the sun in Ecuador, 1944
Urgent need to study medicinal plants
3. To find new molecular models in plants
Many times we can take a plant chemical and modify it or make synthetic copies
of it that are very valuable to us.
Lippia dulcis – sweetener from
Pre-Columbian America
Lippia as a sweetener
In Pre-Columbian America, several plants of the genus Lippia were used as
sweeteners. (F. Verbenaceae – the verbenas).
In the 20th century, L. dulcis was chemically analyzed and a new sweetener was
found, hernandulcin, that is 800 to 1000 times sweeter than sucrose.
Urgent need to study medicinal plants
4. The wide use of plants in folk medicine
One positive aspect of the use of medicinal plants is their low cost compared to
the high price of new synthetic drugs that are totally inaccessible to the vast
majority of the world’s people. Another benefit is that most medicinal plants
don’t have the kinds of harmful side effects seen with synthetic drugs.
Plants and Human Cosmologies
Cosmologies
Cosmologies are branches of philosophy which deal with the origins and
structures of the universe - religions that explain how the universe formed and
our place within it are one kind (a very powerful kind) of cosmology
The Oak of Guernica
Basque coat of arms with
Oak of Guernica
Oak of Guernica by Wordsworth - 1810
THE OAK OF GUERNICA
The ancient oak of Guernica, says Laborde in his account of Biscay, is a most
venerable natural monument. Ferdinand and Isabella, in the year 1476, after
hearing mass in the church of Santa Maria de la Antigua, repaired to this tree,
under which they swore to the Biscayans to maintain their "fueros" (privileges).
What other interest belongs to it in the minds of this people will appear from
the following.
Guernica by Picasso
Moses and The Burning Bush
The sacred Maori Waka Huia
The sacred Maori Waka Huia
Miro tree – Podocarpus ferruginea
Plant biotechnology is transforming agriculture
Plant biotechnology has two meanings
It refers to innovations in the use of plants to make products of use to humans
It refers to the use of genetically modified (GM) organisms in agriculture and
industry
Artificial Selection
Humans have intervened
In the reproduction and genetic makeup of plants for thousands of years
Maize
Is a product of artificial selection by humans
Is a staple in many developing countries, but is a poor source of protein
Interspecific hybridization of plants
Is common in nature and has been used by breeders, ancient and modern, to
introduce new genes
Reducing World Hunger and Malnutrition
Genetically modified plants
Have the potential of increasing the quality and quantity of food worldwide
The Debate over Plant Biotechnology
There are some biologists, particularly ecologists
Who are concerned about the unknown risks associated with the release of GM
organisms (GMOs) into the environment
Issues of Human Health
One concern is that genetic engineering
May transfer allergens from a gene source to a plant used for food
Possible Effects on Nontarget Organisms
Many ecologists are concerned that the growing of GM crops
Might have unforeseen effects on nontarget organisms
Addressing the Problem of Transgene Escape
Perhaps the most serious concern that some scientists raise about GM crops
Is the possibility of the introduced genes escaping from a transgenic crop into
related weeds through crop-to-weed hybridization
Despite all the issues associated with GM crops
The benefits should be considered
Basis of regulation:
Process of biotechnology poses no special risks.
Foods derived from biotechnology should be regulated in the same way as
traditional foods.
Therefore:
The same laws are applicable.
Three federal agencies have responsibility:
US Department of Agriculture (USDA)
Environmental Protection Agency (EPA)
Food and Drug Administration (FDA)
Basis of regulation:
Protecting the US agriculture from agricultural pests and noxious weeds (Federal
Plant Pest Act)
Gm plants:
All plants carrying DNA from an organism considered to be a plant pest (Agrobacterium,
CaMV) are defined as “regulated articles”.
Stepwise procedure for deliberate release of gm plants:
Field trial authorisation (physical confinement),
Determination of non-regulated status (required for unrestricted release and
movement in the US).
A petition for nonregulated status must consider:
harm to other organisms (beneficial & non-target org.),
increase in weediness,
adverse effects on the handling, processing or storage of commodities,
threat to biodiversity.
No tests requirements laid down in the Federal Plant Pest Act.
Generally performed tests to exclude toxic effects:
data from field experiments on the lack of toxic effects on animals (counting),
comparison of the nutritional composition with a conventional counterpart.
61 gm plants are no longer regulated by USDA
(August 2003). These include:
10x maize (HT, IR),
10x tomatoes (PQ),
4x soybeans (HT),
4x oilseed rape (HT),
3x cotton (HT),
3x potatoes (IR, VR).
Basis of regulation:
Manufacture, sale and use of pesticides; environmental safety as well as
tolerance levels for presence in foods
Gm plants:
Substances produced in a living plant to control pests (plant-incorporated
protectants [PIPs]) (e.g. Bt-toxins, viral proteins)
In general, the data requirements for a registration of PIPs are based on those
for microbial pesticides.
These general data requirements include:
product characterisation,
mammalian toxicity (acute oral toxicity),
effects on non-target organisms (avian, aquatic species, beneficial insects,
soil organisms),
allergenicity potential (AA sequence homology, heat / processing stability, in
vitro digestibility in gastric fluids),
environmental fate, and, if appropriate,
insect resistance management.
The exact data requirements for a registration are developed on a case-by-case
basis.
8 plant-incorporated protectants (PIPs) have been
registered by EPA (June 2003):
Bt Cry IA(b) in maize (2x),
Bt Cry IA(c) in cotton,
Bt Cry IIIA in potato,
Bt Cry 1F in maize,
Bt K Cry IA(c) in maize (2x),
Potato Leaf Roll Virus replicase in potato (Monsanto)
Basis of regulation:
- Whole foods are under post-market authority.
- A premarket-approval is only necessary when
substances are added to foods that are not
“generally recognised as safe” (GRAS) Þ Food
additive petition.
Gm plants:
- No pre-market approval necessary.
- All food crops on the market have undergone
voluntary consultations.
- Responsibility (liability) rests with the companies.
Nevertheless, the FDA developed guidance documents for the industry.
US regulation:
different GMOs
Trait / Organism Agency reviewed for:
Insect Resistance / USDA safe to grow
food crop EPA safe for the environment and
human consumption (PIPs)
FDA safe to eat (except for PIPs) and wholesomeness
Herbicide tolerance / USDA safe to grow
food crop EPA use of the companion herbicide
FDA safe to eat and wholesomeness
Modified oil content / USDA safe to grow
food crop FDA safe to eat and wholesomeness
Modified flower colour USDA safe to grow
ornamental crop