Download Lecture 20 The word gymnosperm means “naked seed” the seeds

Lecture 20
The word gymnosperm means “naked seed” the seeds are borne on scales and fruit is not
present.
In gymnosperms the sporophyte is dominant, the gametophyte is not free living so we say the
gametophyte is dependent.
Two major evolutionary advances that appear in the gymnosperms are pollen and seeds.
Know that the following are gymnosperms: Conifers, Cycads, Gingkos, and Gnetophytes and all
are Trachiophytes (have true vascular tissue) and all have secondary growth (wood).
What is pollen? The male gametophyte protected by the spore wall.
When did the earliest seed plants appear? Around 400 million years ago.
What is a seed? It is a plant embryo, with some stored food, enclosed in a seed coat. The stored
food in gymnosperms is primarily female gametophyte tissue. In angiosperms it is endosperm.
In some angiosperms the endosperm is abundant (as in maize) in others the endosperm is
almost completely used up by the time the seed matures (as in beans) and the stored food is
present in the cotyledons.
What are the advantages to seeds? Think about the differences between young sporophytes of
ferns vs. pines. The young sporophytes in gymnosperms can be dormant, can be dispersed by
wind or animals, and are protected. Those are advantages of producing seeds.
Know the definitions of ovule, integument, nucellus, micropyle, and megaspore as related to
the gymnosperm lifecycle. These are on slide 12 of lecure 20.
Gymnosperms are heterosporous and the spores are called the microspore and the megaspore.
Pollen is the immature male gametophyte in gymnosperms. When the pollen lands on a female
cone it grows and matures before it produces sperm cells.
In gymnosperms the megaspore develops into a multicellular female gametophyte.
Some gymnosperms:
Gingko - Dioecious (male and female plants), Large trees with fan shaped leaves. The male
gametophytes produce large flagellated sperm. Ovules are borne on stalks rather than cones.
Cycads - Dioecious, long-lived, compound leaves, seeds dispersed by birds, flagellate sperm,
pollination can take up to 10 years, some pollinated by insects.
Conifers - Most have woody seed cones (do not be confused about conifers with fleshy seeds
such as yews they are not fruit), wind pollination, it takes about two years for conifers to
produce seeds, so a long life cycle compared to angiosperms (or some earlier plants such as
mosses and ferns).
There are many conifer families such as Pinaceae, Cupressaceae, and Taxaceae. You don’t need
to know them for this test but you should learn them if you want to be a Botanist. You need to
know the common features of conifers.
Fascicles - clusters of needles (2-5 in pines, except for pinyon pine which has single needles).
I gave you the lifecycle of Pine as an example of gymnosperm lifecycles and you need to know
the main features: dominant sporophyte generation, dependent gametophytes, the
megasporangium (nucellus) produces a megasporocyte that undergoes meiosis, one megaspore
survives to become the female gametophyte, development of seeds from fertilized ovules,
pollen delivers the male gametophyte to the ovule, in the seed, the embryo is surrounded by
female gamotophyte (1n) tissue, etc.
You need to know that some gymnosperms are deciduous such as larches, dawn redwood, and
bald cypress.
Lecture 21
Angiosperm means seed within a vessel, angiosperms are flowering plants
Important developments in Angiosperms, ovules enclosed in ovaries (the ovary forms the fruit),
pollen enclosed in stamen, double fertilization, further reduced male and female
gametophytes, increases the speed of egg development and pollination.
Advances that appear in angiosperms: improved vascular system with xylem vessels and sieve
tube elements and companion cells (compared to only sieve cells in gymnosperms). Flowers
appear in angiosperms, they aid in pollination and protect developing seeds. Fruit appears and
it is important for dispersal of seeds
In angiosperms the reduced male gametophyte is pollen with two or three cells and the female
gametophyte has seven cells and eight nuclei and is called the egg sac.
There are also strategies in angiosperms to reduce self pollination such as dioecious plant,
timing of pollen/stigma maturity (dichogamy), position of anther and stigma, and self
incompatibility (molecular).
The classic basal angiosperm is Amborella, it has flowers but lacks vessel elements. Other basal
angiosperms are water lilies and star anise.
Note that core angiosperms are magnoliids, monocots, and eudicots.
Eudicots are defined using a single characteristic: tricolpate pollen all eudicots have it and no
other plants have it.
Alismatales are basal monocots.
Characteristics of monocots: single cotyledon, leaves have parallel veins, flower parts in threes,
tems have scattered vascular bundles, absence of secondary growth, adventitious fibrous root
system
The monocot flower is surrounded by bracts: a pair of glumes, a lemma and a palea.
Features of eudicots: net venation, flower parts in fours or fives, two cotyledons, stem vascular
bundles in rings.
Buttercup is a basal eudicot with the following characteristics: - lobed leaves, superior ovary
position (above the petals), seeds with small embryos. So those are basal eudicot
characteristics.
The three largest groups of eudicots are Rosids, Caryophylids, and Asterids.
Lecture 22
Angiosperm reproductive strategies. Self pollination vs. cross pollination. Selfing is good for
pioneer species and it is efficient but cross pollination is important for recombining traits to
generate variation and diversity.
Know the definitions for complete, incomplete, perfect flowers, staminate, pistillate flowers on
slide 21, lecture 22.
For the life cycle of angiosperms you should know all about the male and female gametophytes.
What are the cells that undergo meiosis? What are the cells that are produced by meiosis?
Know about pollen, the egg sac, double fertilization. I will ask at least five questions about the
angiosperm lifecycle.
Polinators:
Insects, birds, mammals, some reptiles and amphibians.
Lecture 23
Know the parts of a flower. The pollen is produced in stamens. It lands on the stigma, hydrates
and germinates. The pollen tube grows down the style and towards the ovules. The synergid
cells of the female gametophyte secrete attractants that are recognized by the pollen tube
which grows towards the ovule. When the pollen tube arrives at the egg sac, it bursts and one
of the synergids bursts. The sperm cells are released and one fuses with the egg and one fuses
with the central cells. Therefore, both the egg cell and the central cell are fertilized. The
fertilized egg becomes the zygote, the first cell of the sporophyte generation. The fertilized
central cell becomes the endosperm, a triploid tissue used as food by the embryo.
I will ask you one or two questions about the genetics of angiosperm gametophytes. Remember
that they are haploid. If a plant is heterozygous (Gg for example) then male and female
gametophytes will be either G or g. If one of the genotypes performs better than the other then
an aberrant segregation will be observed. Normally if you self Gg you expect a ratio of 1:2:1 in
the progeny (1GG, 2Gg, 1gg). If G pollen is normal and g pollen is lethal than what ratio would
you expect in the progeny? 1GG:1Gg.
The ovule develops into the seed, the ovary develops into the fruit. The seed coat is maternal
sporophyte tissue.
The fruit wall is called the pericarp. There are potentially 3 layers, the exocarp (skin), the
mesocarp (flesh) and the endocarp which might be hard or tough.
Name two accessory fruits: strawberry and pineapple.
Lecture 24
Population: more than one individual of the same species
Community: all of the populations together in one place (plants, fungi, animals, protists and
prokaryotes)
Ecosystem: the community along with the physical, non-living environment
A habitat is the set of conditions in which an organism completes its life cycle
operational habitat is the subset of conditions that affect the organism.
Habitat components: abiotic are non-living components such as temperature and biotic or all
living components.
Abiotic components we discussed in class: temperature, moisture, latitude (day length),
disturbances.
Biotic components: How do pioneer species change the soil? How old are soils in Canada and
Alaska? What are the two main types of soils in Minnesota (alfisols and mollisols) and under
what vegetation did they form (alfisols from forests and mollisols from grassland).
What are very old soils called? Ultisols, oxisols, paleosols.
Know the definition for mutualism, amensalism, commensalism, and predation.
Know about limiting factors, local distribution and allelopathy.
For N cycle know:
Denitrification: returning nitrogen to the atmosphere in the form of N2
Nitrogen mineralization converting organic forms of N such as amino acids to the inorganic
form NH4+
Nitrogen immobilization is the opposite: NH4+ -> organic N
Nitrogen fixation: atmospheric N2 to NH4+
Know the mechanisms for N2 fixation: biological (bacteria and cyanobacteria), industrial (HaberBosch process, lightning, photochemical reactions in the atmosphere.
Know why NO3- is toxic to animals. Know about the Diaphorase I mutation I discussed and the
Family of Martin Fulgate.
Know about the carbon cycle. Know approximately the concentration of CO2 in the atmosphere
and how CO2 is added to the atmosphere and is removed (such as photosynthesis).
Lecture 25
Know that many plants and animals were first domesticated around 10,000 years ago in parallel
in several places around the world.
Know that many crops contain extensive genetic rearrangements associated with
domestication.
Know a few plant breeding procedures that result in genetic changes but are on considered
genetic modification, such as mutagenesis, “wide crosses”, tissue culture, induced polyploidy.
Adding a gene from another species results in what most people consider Genetically Modified
Organisms (GMOs).
CRISPR/Cas9 is method to do targeted gene editing and possibly a way to generate genetic
changes in plants without a GMO label.
Know the main modifications in current GMO crops: insect resistance, herbicide resistance,
stress resistance, disease resistance.
Roundup Ready (herbicide resistance) was achieved using a modified EPSP synthase. The
modified EPSP has two amino acid changes that make the enzyme resistant to glyphosate.
Herbicide resistance is the most popular trait in GMO crops. It results in much less conventional
tillage - saving fuel costs and reducing erosion.
Virus resistant papaya was generated by expressing virus coat protein in the plant.
Two ways to generate a transgenic plant are using the gene gun (biolistic transformation) and
via Agrobacterium.
The Flavr Savr tomato was the first GMO plant approved for human consumption. It had
reduced polygalacturonase (PG) activity due to expression of an antisense construct. The result
was that the fruit remained hard during ripening and would hold up better during shipping.
What is Bt? It is short for Bacillus thuringiensis the bacteria that makes the Bt toxin. BT crops
are modified to express the Bt toxin, a protein that is toxic to insects. This results in a large
decrease in insecticide use compared to conventional crops.
Golden rice is a GMO that has a 23-fold higher concentration of -carotene, a precursor to
Vitamin A. This was achieved by introducing two genes, one from bacteria and one from
daffodil.
The arctic apple has a silenced PPO gene that encodes the enzyme polyphenol oxidase. It does
not turn brown when cut. This has been approved by the USDA.
The CRISPR-edited mushroom also has reduced polyphenol oxidase (PPO) and does not turn
brown when cut. This is not regulated by the USDA because it was made using CRISPR.
Lecture 26
Know definitions for
Genetic diversity - genetic differences within a species.
Domestication – conversion of plants or animals to domestic uses.
Know some common characteristics of domesticated crops such as: increased reproductive
investment, increased fruit or seed size, uniform ripening, no seed dormancy, uniform
germination, loss of seed dispersal mechanisms (hairs, burrs etc), non-shattering seed, nondehiscent fruit, annual life cycle.
Non-shattering is often regarded as the hallmark of domestication in most seed crops because
it renders a plant species primarily dependent on humans for survival and propagation:
Also most crops and their wild relatives are self-pollinating. This may be so that the crop
“breeds true” and is genetically isolated from wild relatives.
Domestication of crops occurs through selection and results in a genetic bottleneck in which
only a portion of the genetic diversity available in the wild population is captured in the
domesticated crop. This means that many important gene such as disease resistance genes can
be introgressed into crop varirties.
Domestication genes are the genes that were selected and that result in the domesticated
crop. There are usually only a few genes necessary to convert a wild relative into a crop. And
the domestication genes are usually transcription factors that control the expression of many
genes.
What are characteristics of green revolution plants? – these are generally semi dwarf varieties.
Higher levels of fertilizer can be applied to these varieties and they are lodging-resistant (they
are less likely to fall over if high fertilizer amounts are applied).
The wild precursor to maize is teosinte.
What is hybrid vigor? It is also known as heterosis. It is an increase in growth and yield when
most genes are present in a heterozygous condition. This is achieved by crossing two inbred
(homozygous) parents to obtain the hybrid seed.
The Svalbard seed vault is a repository for plant genetic diversity that could be used to
introduce wild genes into crop varieties.
Lecture 27
In the rhizobium/legume interaction you should know that it is a mutualism and the bacteria
supplies the plant with fixed nitrogen and the plant supplied the bacteria with fixed carbon.
You should know that only prokaryotic organisms (bacteria and cyanobacteria) can fix nitrogen
and the enzyme they use to do that is nitrogenase.
An example of a nitrogen fixing interaction is the cyanobacteria Anabaena interacts with the
aquatic fern Azolla to fix nitrogen. This can occur in rice paddies and will supply N to the rice
plants.
In the rhizobium/legume interaction the plant produced flavonoids to attract the bacteria. The
bacteria produces Nod factor to induced the plant root hairs to produce an infection thread.
The bacteria enter through the infection thread and induce the plant to produce an organ
called the nodule. The bacteria change shape and are then called bacteroids. Within the
nodule, the bacteroids are surrounded by the peribacteroid membrane. The space surrounding
the bacteroid is called the symbiosome. The plant maintains oxygen levels near active
bacteroids at very low levels and produces the protein leghemoglobin to carry oxygen to the
bacteroid.
There are two main types of Mycorrhizal interactions both are plant/fungal interactions. One
type is Arbuscular Mycorrhizal interaction and that occurs between Glomeromycota fungi and
around 80% of plants. The other is Ectomycorrhizal interaction and that occurs between
Basidiomycota or Ascomycota and gymnosperms or angiosperm trees. These are also
mutualistic interactions, the fungi receive fixed carbon and the plant gets greater access to
phosphorus from the soil.
Ectomycorrhiza colonize the apoplastic (cell wall) space between cells while Arbuscular
Mycorrhiza produce arbuscules to transfer material between the fungus and the plant.
In the 1800s plant diseases were known to be caused by bacteria, fungi, and viruses.
The disease triangle indicates that plant disease can occur when the pathogen can overcome
the plant's defenses, the host is susceptible and the weather is favorable for disease.
Plant pathogens can be biotrophic or necrotrophic. You can look up what that means in the
lecture notes.
Some plant defenses we discussed are callose deposiiton, reactive oxygen (ROS) productions,
phytoalexins.
Plants use R proteins to detect pathogen-produced chemicals (called effectors). When R
proteins detect a pathogen, plant defenses are triggered. Plants have many R genes.