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Plant reproduction
• plants have two choices for reproduction: asexual and
sexual
• asexual reproduction – vegetative growth
– portion of the plant is taken from the mature sporophyte
and used to create a brand new plant
Germinated pollen grain
– this results in a genetically identical progeny Anther (n) (male gametophyte)
– this is an advantage if the plant shows superior qualities
• e.g. McIntosh apple Pollen Ovary
• e.g. varietal grapes tube Ovule
Embryo sac (n) (female
– or a disadvantage because there is no genetic variability gametophyte)
which is crucial for the health of the plant as a species
FERTILIZATION
• sexual reproduction – production of sex gametes
Egg (n)
followed by their fusion and the creation of an embryo Mature Sperm (n)
Zygote
that is reliant upon the female gametophyte sporophyte
plant (2n) (2n)
– diploid sporophyte produces haploid spores via meiosis Seed
Key
– the spores divide by mitosis to generate a gametophyte Haploid (n)
Seed
– the gametophyte contains the small male and female Diploid (2n)
Embryo (2n)
haploid plants that produce gametes (sporophyte)
Germinating
– fertilization results in the production of a diploid zygote seed Simple fruit
which eventually becomes a diploid sporophyte via Simplified angiosperm life cycle
mitosis
Flowers Stamen
Anther Stigma Carpel
Style
• flowers – reproductive shoots of the angiosperm sporocyte Filament Ovary
• composed of four whorls of floral organs: sepals, petals, stamens and carpels
– pistil – single carpel or a fused carpel
• complete flowers have all four of these floral organs
– all have functional stamens and pistil
Sepal
• incomplete flowers lack one or more Petal
– some have functional reproductive parts Key
– most incomplete flowers have either a stamen or a pistil Haploid (n)
Receptacle
Diploid (2n)
• stamens – staminate flowers
• pistil – pistillate flowers or carpellate An idealized flower
• flowers can be described using the following:
– 1. symmetry – bilateral symmetry: the flower can be divided into two equal parts by an
imaginary line
– e.g. orchid
• radial symmetry – sepals, petals, stamens and carpels radiate out from a center
– e.g. daffodil
– 2. ovary location – superior ovary: ovary is located above the receptacle
• inferior ovary – located within the receptacle
• semi-inferior – in between
– 3. floral distribution – vary from individual flowers to clusters of flowers called
inflorescences
• e.g. sunflower – center is an aggregation of incomplete flowers that do not develop
• in each undeveloped flower are the male and female reproductive parts of the flower or they may be
sterile
– 4. reproductive variations – presence of staminate and carpellate flowers on the same plant is
a monoecious plant (bisexual)
• presence of either staminate or carpellate flowers– dioecious plant (unisex)
Flower types
• composite flowers
• well represented in your own backyard
• chicory, dandelion, mums, sunflowers, dahlias,
zinnias, lettuce, Black-eyed Susan
• the composites have miniaturized each flower
and then pack them next to each other on a
receptacle
• some composite flowers are composed of ray
and disc flowers, some just one type
disc flower ray flower
• Echinacea blossoms such as the one at the left are typical
members of the Composite Family
• However, certain features do distinguish them from all other
Composites.
• For example, you can see that Echinacea's central ray flowers
are distributed over a hill-like receptacle, making the cluster
of ray flowers look a little like a porcupine. Most composite
blossoms have flat or only slightly elevated receptacles. Also
in that picture notice that the involucral bracts are long and
slender, green, stiff, and pointed downward. The involucral
bracts of most composite blossoms are more triangular, closer
packed with one another, and pointed upward, not downward.
• At the left you see more special features that make an
Echinacea flower an Echinacea flower. First, notice that the
ray flower bears no stigma. That's because in Echinacea the
ray flowers are sterile. They don't have functional female
parts and therefore the item at the base of the flower does not
develop into a seed-like achene. In Echinacea the ray flower is
strictly for drawing attention to the flower by pollinators. Ray
flowers of many composite blossoms do produce viable
achenes, and thus do have conspicuous stigmas.
• Echinacea disk flowers have two unusual features. First,
notice the large, stiff, orange-tipped, scoop-shaped
receptacle bract partially folding around the flower. Many
composite blossoms have no receptacle bract at all, and the
vast majority of those who do have bracts that are much
smaller, softer, and pale to transparent. In fact, when you look
at an Echinacea blossom's center, the pointed things you think
must be the disk flowers are actually bracts. Remember that in
flowers a bract is a modified leaf.
• Mums, or Chrysanthemums, are classic composites -- they are "composite
flowers". In other words, the mum blossom at the right is actually a collection
of hundreds of flowers. Each tiny, orange bump in the flower's center is the
top of a disk flower. Each white "petal" is a ray flower. Each of the many
disk and ray flowers at the right bears a regular blossom's male and female
parts.
• When we speak of mums, we're referring to any of many species belonging to
the genus Chrysanthemum, of which there are well over a hundred. The word
"Chrysanthemum" is both the Latin name and the English name, which often is
not the case.
• If you make a cross-section of the above flower, here is what you see:
This picture shows how the disk flowers are stacked on their bottoms atop the platform-like receptacle. At the right you can see
that better. Also, at the base of each disk flower you can see the future "seeds," which are actually special composite-flower fruits
known as achenes. Once the flowers are pollinated, the achenes will enlarge and harden. When you buy "mum seeds" for sowing
in your garden, you buy those achenes.
As is typical of composite flowers, the Chrysanthemum's flower heads arise from a cuplike collection of scale-like bracts, like the
ones at the right. In some composite species the bracts are very slender and in others very wide, sometimes they are other than
green, and sometimes they are arranged in just one series so that they stand side-to-side instead of overlapping like those above.
• in angiosperms, pollination is the transfer of pollen from an anther to a stigma
• process of pollination requires pollinators – agents that carry or move pollen grains from the anther to the
stigma of the carpel
• flower traits that attract different pollinators are known as pollination syndromes
• many ways to pollinate a female stigma
–
–
1.wind
2. water
Pollination
– 3. insect
– 4. animal
• biotic pollination: pollination by animals (organisms)
– 80% of all pollination is biotic
– entomophily – pollination by insects
• e.g. bees, wasps, ants, beetles, moths and butterflies
– zoophily – pollination by animals
• e.g. birds and bats
• abiotic pollination: pollination by non-animal factors
– Amenophily – pollination by wind (98% of abiotic pollination)
– Hydrophily – pollination by water (aquatic plants)
• pollination in agriculture – seeks to protect and enhance present pollinators
– often involves the culture and addition of pollinators to crops – e.g. commercial fruit orchards
– largest manage pollination event is the California almond orchard industry – nearly 50% of all US produced honey
bees are trucked to these orchards each spring (one million hives)
– New York‟s apple crop requires 30,000 hives and Maine‟s blueberry crop requires 50,000 hives each season
– bees are also brought to commercial crops of cucumbers, squash, melons, strawberreis
– bee species other than honey bees are also used – e.g. bumblbees – greenhouse tomatoes
• ecology and financial importance – insect pollination improves yield and quality
– the vicinity of a forest or wild grasslands can improve yields of apples, almonds and coffee by 20%
• pollination also requires consideration of the pollenizer
– pollinator = agent that moves the pollen
– pollinizer – the plant that provides the pollen
– some plants are self-fertile or self compatible and can pollinate themselves
– other plants have chemical or physical barriers to self pollination and need to be cross-pollinated
• therefore pollination can be either through: cross-pollination or self-pollination
• in monoecious plants – there are mechanisms that ensure the male does not pollinate the
female on the same flower or plant
– recognition factors that prevent self-fertilization – ensures genetic variability
• may be similar to an “immune system” in the plant
• recognizes “self” in the proteins displayed on the pollen
• this system would reject “self” – opposite to the animal immune system
• S-proteins on the pollen grains are recognized by proteins on the surface of the stigma
• dozens of alleles for the S genes exist – similar alleles will be recognized as “self” and rejected
• self-recognition blocks the formation of the pollen tube and can occur through on of two molecular
mechanisms
• 1. gametophyte self-incompatability
• 2. sporophyte self-incompatability
– self-incompatability – the ability of a plant to reject its own pollen and the pollen of closely
related individuals
• gametophyte self-incompatability – S allele in the pollen grain governs the blocking of fertilization
– parental sporophyte – genome = S1S2 gives rise to pollen grains that are S1 or S2 classification
– an S1 pollen grain will not fertilize an S1S2 egg but will fertilize an S2S3 flower while the S2 pollen grain will
not fertilize either
– involves the enzymatic destruction of the RNA within the pollen tube – RNA degradaing enzymes called
RNases are produced by the cells of the style and enter the pollen tube to destroy the male‟s RNA and induce
programmed cell death in the pollen grain
• sporophyte self-incompatability – fertilization is blocked by S-allele gene products in tissues of the
parental sporophyte that adhere to the pollen wall
– neither an S1 or S2 pollen grain will fertilize an S1S2 flower or an S2S3 flower
– signal transduction pathways located in the epidermal cells of the stigma – prevents germination of the pollen
grain
– some plants prevent self fertilization by developing stamens and
pistils at different times or arrange these reproductive parts in
such a way that the animal pollinator cannot accidently transfer
pollen within the flower or plant
• development of two types of flowers – “pin” and “thrum”
• pin flowers – long styles and short stamens
• thrum flowers – short styles and long stamens
– dioecious plants cannot self fertilize –because they only possess
one type of reproductive structure
Stigma Stigma
Anther
with
pollen
Pin flower Thrum flower
Self-pollination vs. Cross-pollination
• cross-pollination – between a pollinator and an external pollinizer
– also called syngamy
– pollen is delivered to a flower of a different plant
– plants adapted to cross-pollinate have taller stamens than the carpels – e.g. thrum type
flower
– e.g. apple crops – due to the grafting of most apple species – gives rise to a genetically
identical orchard
• therefore, each apple stigma would recognize “self” and reject the pollen
• therefore different apple sporophytes with different S alleles must be used
• alternatively – a crabapple limb is grafted to every fifth or sixth tree – genetic variation
• self-pollinization – pollen moves to the female part of the same flower or to
another flower on the same plant
– also called autogamy
– self pollination is restricted to those plants that accomplish pollination without an external
pollinator
• e.g. stamens actually grow in contact with the pistil
– plants adapted to self-pollinate have stamens and carpels at the same length
– cleistogamy – pollination that occurs before the flower opens
• flower is called a cleistogamous flower
• these flowers MUST be self compatible or self-fertile
– many crop plants are self-pollinating
• peas, corn and tomatoes
• routinely self-pollinate
• to prevent self-fertilization – laborious removal of the anthers or through the development of sterile
male plants
• most peach varieties are autogamous – but not truly self-pollinated because the insect transfers
pollen to another flower on the same plant
– cross-pollination can give a better crop
– most crops are self-fertilized
– hybridization – effective pollination between flowers of different species (within the
same genus) or even between flowers of different genera (e.g. orchids)
• many farmers wish to improve their crops by combining genes with other superior plants
• creation of hybrid seeds
Pollination and Honey bees
• Andrena bee
• collect nectar from the flower which is later converted in the hive to honey
• pollen grains are also collected and stored on the hind legs of the bee – as a collection
called a pollen basket
• nectar provides the energy for bee pollination
• pollen provides the protein
• so bees will deliberately collect pollen to meet the growing nutritional needs of the
“building” hive
• a bee that is intentionally collecting pollen for its growing hive is up to 10X more
effective of a pollinator than one intentionally gathering nectar for the mature hive
• so good hive management will ensure that the hives are in the building or brood stage
during the bloom period of a crop
• number of hives per acre of crop
– apples – 1-2
– blueberries – 4
– cantaloupe – 2-4
– cucumber – 1-2
– squash – 1
– watermelon – 1-3
• successful pollination leads to the generation of a pollen tube,
the discharge of sperm and the fertilization of the egg leading
to the formation of the embryo Development of a male gametophyte Development of a female gametophyte
• the anther contains pollen sacs (microsporangia) in which (pollen grain) (embryo sac)
diploid micropore mother cells undergo meiosis to generate 4
haploid microspores
– each has the potential to develop into the male gametophyte Pollen sac
(microsporangium)
– each microspore undergoes mitosis and cytokinesis to create two
separate cells: generative cell and tube cell
–
Mega-
these two cells + spore wall = pollen grain sporangium
– spore wall is unique to the species of plant that creates it Micro-
Ovule
sporocyte Mega-
– during maturation of the male gametophyte – the germinative cell sporocyte
passes into the tube cell MEIOSIS Integuments
– the tube cell produces the pollen tube and as it elongates the Micropyle
germinative cell divides to form two sperm cells Micro-
•
spores (4)
the ovary contains multiple ovules Surviving
– each ovule contains a megasporangium which houses the diploid megaspore
megaspore mother cells that undergo meiosis to produce 4 Each of 4
haploid megaspores microspores Female gametophyte
(embryo sac)
– the subsequent steps can vary from species to species MITOSIS
Ovule Antipodal
– in most angiosperm species only one MG survives cells (3)
– its nucleus divides three times without cytokinesis to give rise to Generative
cell (will
Male
gametophyte Polar
one large cell with 8 haploid nuclei form 2
sperm)
(pollen grain) nuclei (2)
– membranes than form and divide these nuclei up to form the Egg (1)
complete female gametophyte or the embryo sac
Synergids (2)
–
Integuments
within the embryo sac is: Nucleus of
tube cell
• three antipodal cells- at one end of the sac, function unknown
20 µm
• two polar nuclei – not partitioned but share the cytoplasm of the large
Key
central cell of the embryo sac Ragweed
to labels
pollen
• 2 synergids – the other end of the sac, flank the egg and function to grain Embryo
(colorized sac
attract the pollen tube to the egg 75 µm
100 µm
SEM) Haploid (n)
• 1 egg (LM)
Diploid (2n) (LM)
Double Fertilization
• after landing on a receptive stigma – the pollen grain absorbs moisture and
begins to germinate (grow)
• it produces its pollen tube that extends down between the cells of the style
toward the ovary and the ovules
• mechanism of this tube growth is only being elucidated
– presence of a chemoattractant(s) is likely to guide the pollen tube through the style and
toward the ovary
– role of calcium??
• the tip of the tube enters the ovary and two sperm are discharged through the
micropyle in the grain (a gap between the integuments of the ovule)
• the fertilization that results is unique to the angiosperm = double fertilization
– one fertilization event is the typical union of a sperm with an egg to produce the
zygote which divides to form the embryo
– second fertilization event involves the union of the second sperm with the two polar
nuclei – forms a triploid nucleus in the center of the ovule
– this triploid cell gives rise to the endosperm – food storing tissue of the seed
• after double fertilization, the ovule develops into the seed (embryo, endosperm
and integuments)
– endosperm development – usually precedes embryo development
• the triploid nucleus divides and produces a multinucleate “supercell” with a milky consistency
• cytokinesis then converts the multinucleate cell into a multicellular endosperm
• these “naked” cells will eventually produce cell walls and the endosperm will become solid
• the “milk” of the coconut is an example of liquid endosperm and the “meat” is an example of a
solid endosperm
• if the endosperm is used during the development of the cotyledons then the seed will lack an
endosperm as it matures
– embryo development – first mitotic division of the zygote results in an embryo
• splits the zygote into a basal cell and a terminal cell
• terminal cell gives rise to most of the embryo
• the basal cell continues to divide transversely and produces a thread of cells = suspensor
• the suspensor is the “umbilical cord” anchoring the embryo to its parent
• functions in the transport of nutrients to the embryo from the parent
• in some plants the suspensor functions in the transfer of nutrients from the endosperm
Pollen
grain Stigma
Pollen tube
If a pollen grain 2 sperm
germinates, a pollen tube
grows down the style
Style
toward the ovary.
Ovary
Ovule (containing
female
Polar gametophyte, or
nuclei
embryo sac)
Egg
Micropyle
Ovule
Polar nuclei
The pollen tube Egg
discharges two sperm into
the female gametophyte Two sperm
(embryo sac) within an about to be
ovule. discharged
One sperm fertilizes
the egg, forming the Endosperm
zygote. The other sperm nucleus (3n)
combines with the two (2 polar nuclei
polar nuclei of the plus sperm)
embryo sac’s large
central cell, forming a
triploid cell that develops Zygote (2n)
into the nutritive tissue (egg plus sperm)
called endosperm.
• the terminal cells divides multiple times to produces a spherical proembryo
attached to the suspensor
• the cotyledons begin to form as bumps on the proembryo
– eudicot is heart shaped at this stage
– in the monocot only one of these bumps will go on to form a cotyledon
Ovule
Endosperm
nucleus
Integuments
Zygote
Zygote
Terminal cell
Basal cell
Proembryo
Suspensor Seeds
Basal cell
Cotyledons
Shoot apex
Root apex
Seed coat
Endosperm
Suspensor
• after the rudimentary cotyledons form – the embryo
elongates Seed coat
– cradled between the two cotyledons in the eudicot is
Endosperm
the embryonic shoot apex including the shoot apical
meristem Cotyledons
– at the other end of the embryo where the suspensor Epicotyl
attaches is the root apex with its RAM
Hypocotyl
– the seed develops specific structures depending on
whether it is a monocot or a eudicot Radicle
• eudicot – bean Castor bean, a eudicot with thin cotyledons
– elongated embryo – embryonic axis
– contains two developing cotyledons attached to the
embyro Seed coat Epicotyl
– below where these cotyledons attach to the embryo –
hypocotyl
– the hypocotyl terminates in the radicle – embryonic root Hypocotyl
– above the attachment of the cotyledons is the epicotyl –
shoot tip with a pair of miniature leaves Radicle
– the majority of the bean is the starch-filled cotyledons
(food source) Cotyledons
• eudicot – castor bean
– reduced cotyledons in size
– retain their food supply in the endosperm rather than the Common garden bean, a eudicot with thick cotyledon
cotyledons
– the cotyledons receive their nutrition from the endosperm
and transfers it to the rest of the embryo as it grows Pericarp fused
Scutellum
• monocot – corn kernel (cotyledon) with seed coat
– single cotyledon
– in the grass family (including corn and wheat) – the Endosperm
cotyledon is specialized and forms a scutellum Coleoptile
Epicotyl
– the embryo of grasses is enclosed within two shields:
coleoptile which covers the shoot and the coleorhiza Hypocotyl
which encloses the young root Coleorhiza
• during the last stages of seed maturation – the seed dehydrates until Radicle
about 5-15% total water content and becomes covered by the
integuments which have hardened into a seed coat Maize, a monocot
– the cotyledons and embryo become dormant
Fruits
• while the seed is developing from ovules, the fruit is developing from the ovary
• fruit = ripened ovary + seeds of a flowering plant
• fruit protects the developing seeds and will participate in their dispersal using wind or animals
• two main types of fruits: dry and fleshy
• dry fruits
– the ripening of a dry fruit involves the aging and drying of the fruit tissues
• fleshy fruits – a complex series of hormonal changes results in an enticing edible fruit that attracts animals
– the fruits pulp becomes softer due to enzymes that digest components of the cell wall making the flesh of the fruit softer
– usually a color change from green to another color
– organic acids and starch increase in concentration – sweet or tart fruit
• fertilization of the egg triggers a series of hormonal events that triggers the development of the ovary into the fruit
• as the fruit develops, the other parts of the flower die and drop away
– tip of the pea pod is the remnant of the stigma
• the fruit ripens about the same time the seed has finished its development
– accelerated through the production of ethylene
• pollination precedes fertilization – therefore fruit development is usually a sign of pollination
• as the fruit develops the outer wall of the ovary thickens and develops into the pericarp
– tissue that develops and surrounds a seed
– develops from the wall of the ovary
– in some fruits the pericarp can become dry and hard and form a shell
• in fleshy fruits the pericarp can be divided into several regions:
– exocarp – or epicarp
• tough outer skin of the fruit or the peel
– mesocarp – or sarcocarp
• botanical term for the succulent and fleshy middle layer of the pericarp
• usually the part of the fruit that is eaten
– endocarp – hard inner layer of the pericarp of some fruits that contains the seed
– very noticeable in the cherry family, the apricot family, the plums
– it is the pit!
Types of fruits Stamen Ovary
Stigma
• several types of fruits depending on their developmental origin Ovule
– 1. simple: derived from a single carpel or several fused carpels Pea flower
within one pistil Seed
• can be either fleshy or dry
• the dry fruits can either be dehiscent (opening to discharge seeds) or
indehiscent (not opening to discharge seeds) Pea fruit
• if the pericarp is fleshy – fruit is known as a simple fleshy fruit Simple fruit
• e.g. apple, peach, pea, wheat, coconut, nuts, carrot, radish, beet,
tomato, avacado Carpels
– 2. aggregate – results from a single flower that has more than one
separate carpel with each forming a separate “fruitlet”
• develops from multiple simple pistils with one carpel each Stamen
• the fruit is frequently called a “druplet” (raspberry) or a bramble
(blackberry) Raspberry flower
– 3. multiple – develops from an influorescence (a group of flowers Carpel Stigma
tightly clustered together) – the walls of the ovaries thicken and (fruitlet) Ovary
fuse together Stamen
• e.g. pineapple, mulberry, breadfruit
– there are fruits in which structures other than the ovary contribute Raspberry fruit
to the formation of the fruit Aggregate fruit
• these fruits are called accessory fruits or false fruits
• e.g. apple flowers – the ovary is embedded in the receptacle (inferior
ovary) and the fleshy part of the fruit is derived mainly from the Flower
enlargened receptacle
– only the apple core develops from the ovary
• e.g. fig
• e.g. strawberry Pineapple inflorescence
-aggregate accessory fruit consisting of an enlargened Each
receptacle embedded with tiny one-seeded fruits contained with segment
achenes – outer surface of the strawberry develops
from the
carpel
of one
flower
Pineapple fruit
Multiple fruit
Strawberries
• Fragaria
• more than 20 named species
• many hybrids and cultivars (plant that has received a name under the
International Code for Nomenclature of Plants)
• most common are cultivars of the Garden strawberry – Fragaria ananassa
• accessory aggregate fruit – the fleshy part is derived from the peg at the
bottom of the hypanthium – that holds the ovaries
• so the seeds on the outside are the actual fruits with the flesh of the
strawberry a modified receptacle
• classification of the strawberry species is based on the number of
chromosomes
• 7 basic types of chromosomes that each species has in common
• but each species may exhibit different polyploidy
– some species are diploid (14 chromosomes), others triploid, tetraploid, hexaploid,
octoploid or decaploid
Kingdom: Plantae
• the more chromosomes the more rubust the plant is
• strawberries can reproduce asexually through above ground stems called Division: Magnoliophyta
stolons – new plants will form at the nodes and will develop root structures Class: Magnoliopsida
• many strawberry species do not have male reproductive structures
– some have only female and some species are monoecious Order: Rosales
– these female only plants are pollinated by the monoecious ones Family: Rosaceae
Subfamily: Rosoideae
Genus: Fragaria
L.
Coconut, meat, raw
• coconut – fruit not a nut but a seed Nutritional value per 100 g
• known as a fibrous drupe – not a true nut
• husk = mesocarp composed of fibers called coir Energy 350 kcal 1480 kJ
– coir is used to make rugs, mats, brushes, potting
compost
• inner stone = endocarp with three germination 15.23
Carbohydrates
pores at one end, contains the endosperm which g
is edible
- Sugars 6.23g
• one of these pores will allow the growth of the
embryonic root – the radicle - Dietary fiber 9.0 g
• mature coconut fruits drop from trees and can
appear dead for months until a small green shoot 33.49
pushes out from the coconut Fat
g
– many changes prior to this emergence
– at the end where the three „eyes‟ are located – the Protein 3.3 g
–
embryo begins to grow
the embryo feeds off of the “milk” (liquid
endosperm – coconut water) and the “meat”
(solid endosperm = testa)
Fruits Thiamin (Vit. B1) 0.066
mg
5%
– the embryo fills the space within the seed Riboflavin (Vit. B2) 0.02
• the embryo will sprout out of the shell and will -flowers of the coconut palm are mg
1%
become a young coconut seedling
• one large coconut (unripe) can contain up to 1 polygamomonoecious Niacin (Vit. B3) 0.54 mg 4%
liter of coconut water (both male and female parts in
• water is a combination of sugar, fibre, proteins, the same influorescence) Pantothenic acid
6%
anti-oxidants and vitamins (B5) 0.300 mg
– can be used as an IV fluid!
-flowering occurs continuously
• coconut milk = combination of grated coconut with the female flowers Vitamin B6 0.054 mg 4%
flesh + warm water to extract out the aromatic producing the seeds Folate (Vit. B9) 26 μg 7%
compounds and oils
• if left to set the coconut cream will rise to the top
-most are cross-pollinated Vitamin C 3.3 mg 6%
• the sap can be harvested and fermented to
produce palm wine or “toddy” or can be boiled to Calcium 14 mg 1%
produce a sweet syriup Iron 2.43 mg 19%
• interior of the growing true stem can be harvested
and eaten – heart-of –palm (kills the stem) Magnesium 32 mg 9%
• the meat can be dried to form copra – main Percentages are relative to US
source of coconut oil Phosphorus 113 mg 16%
recommendations for adults.
• coconut roots can be used as a dye Source: USDA mg
Potassium 356 Nutrient database8%
• the trunk can be harvested for palmwood
Zinc 1.1 mg 11%
Seedless fruits
• seedlessness is an important feature of many commercial fruit crops
• bananas, pineapples, grapes, watermelons, some citrus fruits (navel
oranges, tangerines)
• in some species, seedlessness is the result of parthenocarpy = fruits set
without fertilization
– may or may not require pollination
• most species require some sort of pollination stimulus
– pollination triggers fruit development within the ovary but the ovules
abort the embryos and do not produce mature seeds (stenospermocarpy)
• some fruits will become seedless if the plant does not undergo
pollination but will develop seeds if pollination takes place and results
in fertilization within the ovules
– e.g. pineapple, cucumber
• seedless watermelons are grown from seeds – seeds are produced by
hybridizing diploid and tetraploid lines of watermelons – resulting
seeds are sterile triploid plants with no reproduction
– fruit development is triggered by pollination but no fertilization takes
place
•
Bananas and Plantains
Musaceae
• originated in the Indo-Malaysian region to northern Australia
• banana = seedless fruit produced from triploid plants
• plant possesses three sets of chromosomes
• this prevents meiosis and the plant does not generate mature gametes for
sexual reproduction
• such plants can arise from spontaneous mutations or through hybridization
between diploid and tetraploid individuals
• the banana is usually propagated vegetatively through the production of
“pups” – offsets that are genetically identical to the parent
– grow off of the rhizomes
– large pups are preferred as planting materials
• grow from underground rhizomes with fleshy pseudostems that grow
vertically above ground
• the true stem forms 10-15 months after planting and pushes through the
pseudostem/stalk producing the terminal influorescences that will produce
the fruit
• each banana stalk produces one huge flower cluster and then dies
• new stalks grow from the rhizome
• flower – shoots out from the tip of the true stem as a single structure
• is a large purple-clad bud – as it opens slim, nectar rich white flowers appear
as a whorled cluster with a deep red bract covering them
• the flowers of the first 5 to 15 rows are female – the develop without
pollination to form clusters of fruits called hands – technically a berry
– these produce the fruits
• as the influorescence elongates – sterile flowers with abortive male and
female parts now arise, followed by normal staminate flowers and carpellate
flowers with abortive ovaries
• as a seed matures it dehydrates and enters a dormancy phase – low metabolic rate in the embryo and a
suspension of its growth and development
• conditions required to break this dormancy varies from plant to plant
– e.g. once they reach a suitable environment
– e.g. some require a specific environmental cue
• seed dormancy increases the chances that the seed will germinate under favorable conditions
• environmental conditions
–
–
desert plants – require substantial amounts of water
trees – heat provided by fires
Seed germination
– extended exposure to cold
– lettuce – requires increased light
• germination depends on the physical process called imbibition
– uptake of water due to the lower water potential of the dry seed
– causes the seed to expand and rupture its coat
– also triggers metabolic events in the embryo that enables it resume its development
– as the embryo grows it makes digestive enzymes which digests away the stored foot in the seed (endosperm or cotyledons)
– first organ to emerge is the embryonic root – the radicle
– the shoot tip then forms and breaks through the soil surface
– in many eudicots and beans – a hook forms in the hypocotyl and this hook is pushed through the soil – stimulated by light to
straighten which raises the cotyledons and the epicotyl
• the shoot apex is actually pulled upward rather than being pushed tip first through the abrasive soil
• the epicotyl spreads its first leaves which are called true leaves as apposed to the “seed leaves” or the cotyledons
– in monocots breaking ground is accomplished by the coleoptile
• the sheath enclosing the coleoptile pushes upward through the soil and into the air
• the shoot tip grows through the tunnel forming within the growing coleoptile
• the shoot then breaks through the tip of the coleoptile
Foliage leaves
Cotyledon
Epicotyl Foliage leaves
Hypocotyl
Cotyledon Cotyledon
Hypocotyl Coleoptile Coleoptile
Hypocotyl
Radicle
Seed coat
Radicle
Common garden bean Maize
Asexual
reproduction
• to ensure successful germination of a seed and embryo – the conditions must be very favorable
• some plants will produce numerous seeds in order to ensure survival of a few embyros
• this is very expensive energy wise
• some plants reproduce asexually and produce an exact copy of themselves
• does not allow for genetic recombination
• result is essentially a clone
• in seedless plants, some gymnosperms and some angiosperms – reproduction can be either sexual or asexual
• if a plant is superbly adapted to one environment and is very successful – then asexual reproduction would be
advantageous – if the environment remains the same
• also known as vegetative reproduction
• is an extension of the capacity for indeterminate growth owing to the presence of meristematic tissues
• in addition the parenchyma of some tissues can specialize and divide to create different kinds of tissue
• fragmentation – separation of a parent plant into parts the develop into whole plants
– one of the most common modes of asexual reproduction
– e.g. root system – branches off to form adventitious roots which give rise to separate shoot systems and separate plants
– produced the oldest known plant clone – creosote bushes of the Mojave desert
• production of bulbs
• production of suckers from exisiting root systems
• apomixis – “away from the act of mixing”
– production of plants asexually
– reproduction of dandelions
– produce seeds without pollination or fertilization
– diploid cell in the ovule gives rise to the embryo and the ovule matures into seeds
– seeds are dispersed as windblown fruits
– e.g. dandelions, Kentucky bluegrass
Vegetative growth and agriculture
• cuttings – many houseplants, woody ornamental plants and orchard trees
– asexually reproduced from plant fragments called cuttings
– some cuttings come from the shoot or stem
– at the cut end of the shoot – mass of undifferentiated cells forms – callus
– from this callus is the development of adventitious roots
– if the plant is cut at a node – no callus forms but adventitious roots still do
– the African violet can be propagated from single leaves
– the potato can be cut into several pieces each containing a vegetative bud of “eye”
that regenerates a whole plant
• grafting – modification of reproduction from cuttings
– a twig or bud of one plant is grafted onto a plant of a closely related species or the
same species
– combines the best qualities of plants
– usually done when the plant is young
– the plant that provides the root system = stock
– the twig grafted onto the stock = scion
– e.g. grape varietals
– e.g. dwarf trees – made by grafting normal twigs onto the stocks of dwarf varieties
• the dwarf quality retards the normal growth of the twig – dwarf plant
• test-tube cloning – in vitro methods to create and clone plants
– culturing of small pieces of tissues cut from a parent plant = explant
– explant is cultured on artificial media containing the nutrients and hormones
required to grow the plant
– explant can very from single parenchyma cells to pieces of tissue
– a callus will form and sprout shoots and roots
– test tube plantlets are then transferred to soil
– can also subdivide the callus and increase the number of plantlets that result
– e.g. orchids, pine trees with high wood production
– protoplast fusion – tissue culture methods are used to invent new plant varieties that
can be cloned
• cell wall is removed through treatment with enzymes (cellulases and pectinases)
• produces the protoplast – screened in the lab for the desired genes
• two protoplasts are fused in the lab to produce a new one
• the new protoplast regenerates a wall and can be cultured into a callus
Just a few The callus
parenchyma cells differentiates into
from a carrot gave an entire plant,
rise to this callus, with leaves, stems,
a mass of and roots.
undifferentiated
cells.
Biotechnology
• artificial selection – the process of selecting for specific, desired traits in an organism
– corn – “unnatural monster” created by humans
• modern corn would become extinct without our interference
• corn kernels are permanently attached to the central axis (“cob”) and are protected by a tough
overlappng leaf sheath (“husk”
• this results in a plant that cannot scatter its kernels and reproduce
• corn was first domesticated around the Neolithic age – late Stone age
– but selection can be natural
• wheat – result of natural hybridization between different species of grasses
• quite common between plants and can be exploited by farmers for crop improvement and horticulturists
• e.g. corn – most common varieties of corn are poor sources of protein
– proteins very low in lysine and tryptophan
– these are two of the 8 essential amino acids in humans
– 40 years ago – discovery of a mutant corn variety called opaque-2
– this variety had high levels of these two essential amino acids
– but this strain also had a soft endosperm within its seed – vulnerable to attack from pests and hard to harvest
– over the next 20 years – strain acquired a harder endosperm while retaining the amino acids
– can be accomplised easily now using genetic engineering!!
• transgenes – introduction of a new gene into the genome of the plant = GM plants
(genetically manipulated)
– many of these genes are used to increase yields on difficult land conditions
– e.g. cotton, corn, potatoes
• contain genes from many types of bacteria – e.g. Bacillus strains
• e.g. introduction of the gene for Bt toxin into plants can help control pest induced damage
– some plant species have genes that make them tolerant to a number of herbicides that kill insects and
leave the plant intact
• e.g. corn, cotton, sugar beets and potatoes
– can also engineer plants to be resistant to disease
• e.g. papaya resistant to spring rot virus introduced into Hawaiian crops
– human health???
• may transfer allogenes to humans – genes that produce proteins we are allergic to
• but researchers are removing genes from soybeans, peanuts and other crops that are known to cause allergies
• Bt corn contains 90% less of the cancer-causing mycotoxin called fumonism (produced by the fungus Fusarium)
• labelling demands
• but why not naturally produced hybrids???
– transgene escape – introducing transgenes into related wild species that do not have the transgene
• spontaneous hybridization with wild relatives
• not a problem if no wild relatives are nearby – e.g. soybeans
• also the use of “terminator” technology – plants undergoing the last stages of seed or pollen maturation produce
“suicide” genes and will not complete their maturation and reproductive cycle
