Final exam

Question 1

What are the effects of red and far red light on germination?

Answer 1

Red light causes germination, and far red reverts the effect of red light because of the receptors are interconverted.

Question 2

What photoreceptors are for what kinds of light?

Answer 2

Phototropin and cryptochrome: blue light only phytochrome: mostly far red/red light but also can absorb blue light

Question 3

What is photomorphogenesis? How do light and dark grown plants differ?

Answer 3

Plants develop differently in the presence of light than in the presence of darkness. Dark-grown (skotomorphogenesis) plants will have a larger hypocotyl, less green because of a lack of chlorophyll, and less opened cotyledons/no true leaves. The tip of the plant will also have a apical hook.

Question 4

What are the two kinds of phytochrome?

Answer 4

Pr and PFr
Pr is for red light (650-680), light is converted to Pfr (far red recptor) and is a blue pigment.
PFr is for far red light (710-740nm) where the peak is at 730nm. Has a blue-green pigment. When absorbing Fr it is converted to Pr (red receptor)
Two forms of the SAME RECEPTOR and make the other form of receptor.

Question 5

What are photomorphogenic responses?

Answer 5

Some of the developmental responses are:
Germination
Seedling Development
Leaf structure - less/no true leaves, apical hook
Chloroplast development - proplastids become eitoplasts
Tropisms
Flowering

Question 6

What are the two different kinds of phytochrome molecule

Answer 6

Phytochrome I: most abundant in eitolated tissue, transcription is REPRESSED by light. So is the abundant form in the DARK. In PFR form the protein is ubiquated and degraded, but is required for responses to farred light. Accumulates in the nucleus as a response to far red light.

Phytochrome II:
More stable in light, and therefore the most common form in the LIGHT. Involved in the responses to white and red light, and accumulates in the nucleus as a response to it.

Question 7

What is photomorphogenesis?

Answer 7

Photomorphogenesis is the development of the plant within the presence of light. Seedlings in light will have an increased number of true leaves grown, chlorophyll, and shorter hypocotyl growth compared to in the dark

Question 8

What is skotomorphogenesis?

Answer 8

Skotomorphogenesis is the development of the plant in the dark. Seedlings in the dark will have a reduced/no number of true trues, longer hypocotyls, reduced chlorophylls/increased eitioplasts, and an apical hook. Skotomorphogenesis was thought to be the standard default developmental pathway but it is no longer considered that because skotomorphogenesis requires photomorphogenesis

Question 9

What is the receptor of red light?

Answer 9

Phytochrome red

Question 10

What is the structure of phytochrome?

Answer 10

Phytochrome is a protein that is attached to a chromophore. The chromophore for phytochrome is called phytochromobilin and is responsible for the reception of the light. Phytochrome is a polypeptide and is covalently attached to phytochromobilin.

The phytochromobilin’s red and far red variants are different because of their chemical composition. Red light chromophores are trans, while the far red version is cis. Light changes the conformation of the chromophore through cis-trans isomerization.

Question 11

Where is phytochrome in the cell? Does the cellular localization change in response to light?

Answer 11

Phytochrome I:
most abundant in etiolated tissue where it is encoded by PHYA gene and is liable/inhibited by light.
in far-red light, phytochrome 1 will accumulate in the nucleus instead of the etiolated tissue.
Phytochrome II:
Also accumulates in the nucleus in the presence of white/red light. It is more stable in light and is encoded by PHYB/C/D/E

Question 12

What types of pathogens do plants have?

Answer 12

Pathogens
1. Viruses such as tobacco/Cauliflower mosaic virus
2. Bacteria. Examples: bacterial wilt of sweet corn, black rot of crucifers
3. Oomycetes-also known as water molds. These are organisms that have a filamentous growth habit, nutrition by absorption and reproduction via spores, but are different from fungi. They cause diseases such as the late blight of potato, downy mildew of grape vine, sudden oak death, and root and stem rot of soybean.
4. Fungi. Example: The potato blight in Ireland and northern Europe, was caused by the fungal-like organism Phytophthora infestans.
Pests:
Insects, nematodes, mammals and birds

Question 13

What are biotrophs? What are necrotrophs? What is a hemibiotrophic pathogen?

Answer 13

Biotrophic- Plant tissue remains alive. Minimal cell damage.

Necrotrophic- Kill the affected plant cells. Dead tissue is colonized by pathogens and serves as food source.

Hemibiotrophic- Initial biotrophic stage followed by a necrotrophic stage.

Question 14

What routes of entry do pathogens use to infect plants? Do most pathogens have the ability to penetrate the cuticle, plant cell wall and membrane directly?

Answer 14

Pathogens mainly enter through natural openings like the stomata.
Fungi penetrate cells directly, making a hole in the cuticle using penetration pec to drill through the cell wall of leaf and go through.

Bacteria, such as an insect bite, penetrate through the wounding site. Or through natural openings like the stomata

Question 15

What are mangroves? Are they a single plant species or multiple species? How many species are included in this group of plants?

Answer 15

Mangroves are considered salt-tolerant plants. True mangroves are in saltwater coastal environments but are not phylogenetically related to one another, so they are numerous species. Around 54 species are considered true mangroves.

Question 16

What is the function of the TMV movement protein? How does it work?

Answer 16

Mediates viral spread between plant cells via plasmodesmata.

Question 17

Why do we fuse the coding regions of genes to the promoter of the CaMV35S gene when we want to express the genes in plants?

Answer 17

The CaMV35S promoter (from the Cauliflower Mosaic Virus) is used as a backbone to develop various transcription control systems.

Question 18

Can fungi penetrate plant tissue directly? What is an appresorium?

Answer 18

Yes, fungi are able to penetrate plant tissue directly. They use appresorium to get into and infect the plant.

Question 19

What are haustoria?

Answer 19

Found in parasitic plants, haustoria are used to absorb nutrients and water by penetrating through the host’s tissues.

Question 20

What is the difference between a cyst nematode and a root knot nematode? What changes do they cause in plant cells? What is a syncitium? What is a giant cell?

Answer 20

Root knot nematodes cause swelling in the roots. Giant cells are enlarged cells which provide the nematodes with nourishment.

Cyst nematodes swell and form a cyst when they die, but they do not cause the plant itself to swell. Syncitium are feeding structures formed by cyst nematodes within the host plant’s root cells.

Question 21

How do insects feed on plants?

Answer 21

Phloem feeders tap into the plant’s phloem.

Cell content feeders penetrate through the epidermal surface and feed on the cell contents.

Chewing insects use their mandibles to cut leaf tissues for chewing.

Question 22

Why are some plants parasitic? Does this mean they do not photosynthesize?

Answer 22

Parasitic plants tap into the vascular tissues of their host plants using haustoria to take up water and nutrients.

This does NOT mean that they don’t photosynthesize. Some species are unable to photosynthesize, but others are still able to.

Question 23

How has coevolution resulted in several layers of resistance to pathogens in plants?

Answer 23

Selective pressures created by pathogens allowed for plants with more resistance to the pathogens to survive and reproduce better than the plants without resistance. Pathogens would then develop mechanisms to harm the resistant plants, and more defenses would be built from the plants as a result.

Question 24

What is an elicitor?

Answer 24

A molecule that triggers a hypersensitivity response.

Question 25

What are PAMPs/MAMPs?

Answer 25

Pathogens produce PAMPs (pathogen associated molecular patterns)
or MAMPs (microbial associated molecular patterns) that place
selective pressure on the plants.
Plants have a response: PAMPs or MAMPs immunity, that places
selective pressure on the pathogens.

Question 26

How does sensing of PAMPs/MAMPs in the plant cell change the concentration of calcium in the cytoplasm?

Answer 26

PAMP: Pathogen associated molecular patterns.

MAMP: Microbial associated molecular patterns.

Produced by pathogens/microbial organisms which place selective pressures on plants.

1. PAMP interacts with receptor protein
2. Causes signal transduction
3. Opening of calcium channels
4. Increase in Ca+

Question 27

In addition to increasing the concentration of calcium in the cytoplasm, what other changes occur in the plant cells as a result of receptors binding PAMPs on the plasma membrane?

Answer 27

Production of reactive oxygen species (hydrogen peroxide)

Activation of protein kinases with the interaction of reactive oxygen species and Ca+

Question 28

What are ROS? How can ROS fortify the cell wall?

Answer 28

Reactive Oxygen Species

ROS are toxic to pathogens.

Question 29

What are resistance genes in plants and what are avirulence genes in pathogens?

Answer 29

Resistance genes in plants produce receptor molecules which bind to PAMPs/MAMPs

Avirulence genes in pathogens produce effector molecules (PAMPs/MAMPs)

Question 30

What is the gene-for-gene model?

Answer 30

In order for a plant to resist specific pathogens, it must have a gene encoding a receptor specific to the pathogen.

Question 31

Based on the gene-for-gene interaction, what is the difference between plants that are susceptible and plants that are resistant to a pathogen?

Answer 31

The plants that are resistant have a gene which encodes the receptor that provides resistance while the plants that are susceptible don’t

Question 32

What types of proteins are encoded by the R genes in plants? Do these R proteins always bind directly to the product of the avirulence gene as predicted by the gene-for-gene model?

Answer 32

Receptor proteins.

The R proteins bind directly to the Avr products, which leads to other molecules binding to the receptor to produce a defense response.

Question 33

What is the cause of polymorphism of the R gene in natural plant populations? How does that compare to the ability of animals to produce antibodies that recognize multiple antigens?

Answer 33

Various mutations. In natural plant populations, some individuals will resist some pathogens but be susceptible to others, so polymorphism allows the populations to continue existing as there are individuals with various immunity. The population will likely not be wiped out by a singular pathogen as a result.

Question 34

Are antimicrobial compounds produced in plants only in response to attack by microbial pathogens? What types of compounds are produced in plants that are antimicrobial? Do all plant species produce the same compounds?

Answer 34

Only produced in response to microbial pathogens.

Terpenoids, alkaloids, cyanogenic glycosides, glucosinolates, phytoalexins

Not all species produce the same compounds.

Question 35

What is the hypersensitive response to a pathogen? How does this response benefit the plant?

Answer 35

Cell death. Prevents pathogen invasion into the rest of the plant.

Question 36

What is systemic acquired resistance (SAR)? How does this type of resistance in plants compare to immunity in animals?

Answer 36

Defense genes are activated across the entire plant and provides broad immunity. Instead of targeting specific pathogens like in animals, SAR resists various kinds of pathogens even if the plant had never encountered them before

Question 37

What type of molecule is salicylic acid? How is it synthesized in the plants?

Answer 37

Hormone.

Phenylalanine -> trans-cinnamic acid -> benzoic acid -> salicylic acid

Question 38

What evidence supports that salicylic acid plays an essential role in SAR?

Answer 38

After introducing a pathogen to a part of a plant, an increase of salicylic acid concentration is observed.

Question 39

What type of genes are expressed in response to salicylic acid?

Answer 39

Defense genes

Question 40

How are the long distance signals transported in the plant?

Answer 40

Phloem-mobile signals

Question 41

What would have to be the characteristics of the transported signal?

Answer 41

Able to be perceived for defense responses

Question 42

What is the evidence for and against salicylic acid as the signal that travels through the plant in SAR?

Answer 42

FOR: increase in concentration in response to pathogens

AGAINST: a grafting experiment showed that SA is not a transmissible signal -

If the rootstock is transformed and expressing nahG and the scion is from a normal plant, there is SAR, and the lesions on the upper leaf are small. This means that even if SA does not accumulate in the bottom leaf, the signal is transmitted to the upper leaf. Therefore, SA is not the transmissible signal.

If the rootstock is from a normal plant and the scion is from a transformed plant expressing nahG, there is no SAR and the lesions are large on the upper leaf. Therefore, SA needs to accumulate at the site of the second infection for SAR. SA is necessary for SAR although is not the transmissible signal.

Question 43

What compound functions as a long distance SAR signal in tobacco? What is the evidence for this? You should understand and be able to explain the experiments done with the transgenic plants described in the papers.

Answer 43

MeSA: Methylsalicylate

If the rootstock is from a normal plant and the scion is from an SAPB2-silenced plant there is no SAR. If MeSA cannot be converted into SA at the site of the second infection there is no SAR. If the rootstock is from a SABP2-silenced plant but the scion is from a normal plant, there is SAR. As long as SA can accumulate at the site of second infection there is SAR. SA is essential for SAR but it is not the transmissible signal. It does not need to be transported from the rootstock to the scion.

SAMT is SA methyltransferase. If the plant is SAMT1-silenced, there is no production of methyl-SA from SA.

If the rootstock is from a normal plant and the scion is from an SAMT1-silenced plant there is SAR. MeSA is not needed at the site of the second infection.
If the rootstock is from a SAMT1-silenced plant but the scion is from a normal plant, there is no SAR. MeSA needs to be produced on the bottom leaf. MeSA seems to be the transmissible signal.

Question 44

What is systemin?

Answer 44

Induces the systemic wounding response. Required at the site of infection to promote this response.

Question 45

What is the involvement of jasmonate in plant resistance? What compound functions as a transported signal in systemic wound response? You should be able to explain the experiments with grafts and the conclusions from these.

Answer 45

Jasmonates induce a broad spectrum of defensive
responses, production of PIs, the release of volatiles, alkaloid production, etc.

MeJA

the mutant has a perception issue of jasmonate it results in no resistance. Must be local response to jasmonate

when systemin is not perceived by the rootstocks the signals needed cannot be transported

when jasmonate is not produced at the rootstock a functioning signal cannot be produced

Question 46

What evidence supports that volatile signals are also involved in systemic resistance?

Answer 46

ISR induced by the release of volatile signals

Question 47

What are green leaf volatiles?

Answer 47

Rapidly released upon tissue damage and can also act against
pathogens. GLV have the ability to alert nearby plants, attract pest controlling insects,
etc.

Question 48

What is ethylene? What is the role of ethylene in plant resistance to pathogens? Against what type of pathogens does ethylene seem to increase defense responses?

Answer 48

Hormone

ISR is triggered by beneficial microbes like bacteria or fungi which causes ethylene to be
produced and cause a systemic reaction throughout the plant, enhancing its resistance to a wide range of pathogens

For expression of SAR, ethylene
perception is required locally
in the pathogen-infected leaf

ethylene can contribute to resistance against necrotrophic, but not biotrophic pathogens.

Question 49

What are the results of grafting experiments in tobacco between wild type plants and plants insensitive to ethylene? When they grafted wild type scions onto ethylene insensitive rootstocks and reinoculated the scions with TMV, why was the size of the lesions about the same size whether they had first inoculated the rootstocks or not? What is the conclusion from this experiment regarding the need for ethylene sensitivity for SAR in the plant?

Answer 49

• The NahG gene encodes a salicylate hydroxylase
  that converts salicylic acid into non-SAR-inducing
  cate-chol.

-NahG rootstocks,
although unable to accumulate salicylic acid in
response to TMV infection, did produce SAR in wild-
type scions.

-ethylene must be sensed by the plant in order for
ISR

Question 50

What are the advantages of having airborne signaling? In the model of two-step regulation of systemic resistance, what is the function of volatiles?

Answer 50

overcomes restrictions resulting from the plant’s orthostichy. Plant enemies often move from one leaf to the adjacent one, but directly adjacent leaves usually lack direct vascular connections.

volatile signal molecules can reach distal plant parts faster than compounds that
are transported through vascular tissues.

Question 51

How do volatiles affect systemic resistance in neighboring plants?

Answer 51

Triggers SAR in neighboring plants

Question 52

Why are mangroves important?

Answer 52

Mangroves are essential because, environmentally, they foster marine life where fish and other organisms often live within the mangroves for protection. They also provide storm protection against flooding and erosion.

Question 53

Mangroves are facultative halophytes. What does that mean? Do they have a physiological requirement for salt?

Answer 53

There are two different kinds of mangroves, where facultative halophytes refer to the species found in less salty/no salt environments. Facultatives can be affected by excess or low salinity environments, but they can survive without.

Obligate mangroves require salinity for growth and survival.

Question 54

What are some of the morphological and anatomical features that result in the adaptation of mangroves to a saline environment?

Answer 54

Mangroves have adaptations where they have fewer stomata to reduce transportation, smaller and thicker.

Question 55

To what does one of the papers refer to as the “gene revolution”? How does this compare to the “green revolution” of the 20th century?

Answer 55

The gene revolution refers to the use of gene modification compared to the green revolution for hi yield crop yield through fertilizers and irrigation.

Question 56

What are some examples of cultivated genetically engineered plants?

Answer 56

One example is the Hawaiian papaya, where a ring spot virus in 1992 cut papaya production in half. GE-resistant papaya strains were made and produced and then by 2004 the strain accounted for 88% of the crop

Question 57

What is golden rice? How did they make it? What were some of the challenges of this type of rice?

Answer 57

One example is transgenic golden rice, which contains beta-carotene using a 2nd-generation daffodil gene, which was intended to provide more nutrients for those in areas of food scarcity.
It took two generations to figure out the right gene for the crop as the first-generation crop did not produce a high enough percentage of beta-carotene.
The drawback to this crop is the golden color off puts people and discourages them not to consuming the product because it looks “fake”

Question 58

What are some environmental, health and economic benefits of growing transgenic crops?

Answer 58

Reduces the price and chemical use compared to traditional irrigation/fertilizer/pesticide farming practices. GMO plants do not need constant reapplication of treatments in order to be resistant, so it saves farmers the cost of reapplying the treatments. It also reduces chemical use for pesticides and fertilizers and increases biodiversity.

Question 59

What are the main concerns regarding genetically modified crops? What are the health concerns? What are the environmental concerns?

Answer 59

There is a lack of regulation for transgenic crops and a lack of knowledge about what GMOs are and their purpose.
Environmentally, there are concerns for unwanted gene flow of GMO crops, giving the genes to wild, potentially invasive species, which could make them even harder to remove from the native environment.

Question 60

What is the basis of conventional cross-breeding? What are some disadvantages of this traditional method of crop genetic modification?

Answer 60

The basis of conventional cross-breeding is crossing two plants with relevant characteristics and selecting the offspring with the desired combinations of genes inherited from the two parents.
Disadvantages of this method include it being a time-consuming process with limited control, as well as less genetic variability (can add genes from other plants and animals)

Question 61

What are other forms of genetic modification? How is mutagenesis used? What is cisgenesis? What is transgenesis?

Answer 61

Gene-gun editing: agrobacterium mediated transformation, CRISPR and mutagenesis
Mutagenesis: is also called mutation breeding (1920’s) involves subjecting plants to radiation or chemical means to induce spontaneous genetic variation to generate new varieties.
Cisgenesis: involves introducing a gene from a related plant species
Transgenesis (GMO): involves the transfer of foreign DNQ encoding a desired trait into an unrelated plant species. Ex. groundout ready corn is resistant to glyphosate due to genes from agrobacterium CP4

Question 61

What does CRISPR stand for? What is the original function of CRISPR in bacteria? How does it work?

Answer 61

Clustered regularly interspaces short palindrome repeats. CRISPR is a component of immunity in bacteria. DNA from a virus invades the bacteria; the viral DNA is processed into short segments and is made into a new spacer between the repeats. These will serve as genetic segments and become a new spacer between the repeats.
These will serve as genetic memories of previous infections. The CRISPR sequence undergoes transcription, including spacers and Cas genes, creating a single-stranded RNA. The resulting single-stranded RNA, called CRISPR RNA, contains copies of invading viral DNA and guides the CRISPR-associated proteins to them. The protein then cleaves and destroys the targeted viral material.

Question 61

Does the CRISPR name correctly explain what occurs in fungal, plant, or animal cells?
How is it used in these cells?

Answer 61

CRISPR is a misnomer when referencing it as a tool for gene editing in fungal, plant, and animal cells because it references repeats in DNA only found in bacteria. The Cas9 protein with an RNA targeting sequence edits fungal, plant, and animal cells without CRISPRs.

Question 61

What are the advantages of CRISPR over the prior methods of genetic modification used?

Answer 61

CRISPR is much more precise and leaves behind issues like genetic drag found in traditional cross-breeding.

Question 62

What is a possible problem of the CRISPR technique?

Answer 62

Economic:
Gene editing makes produce last long enough to import from overseas growers, diminishing local and national revenue.
Toxins/Allergens:
Appearing in modified food the genetic modification would have to trigger the production of a specific allergen. This hasn’t been documented in GMO food.
GMO pollen escape:
The movement of GMO pollen can result in transferring genetically modified traits to non-GMO or wild relatives. This unintended genetic mixing may alter non-GMO populations’ genetic diversity and characteristics. These traits introduced into wild populations might affect their ecological interactions, competitiveness, or adaptation. Impacts biodiversity.

Question 63

Why is it possible to not consider plants modified by CRISPR genetically modified organisms? Should these plants be exempt of the large number of regulations imposed by the USDA?

Answer 63

CRISPR can be utilized without transgenes to create cisgenic species that do not differ from the products of traditional crossbreeding and would evade the current restrictions of GMOs by the USDA. As the law was written in 1992, these plants would be exempt. RJ thinks the law should be rewritten to be more streamlined and with CRISPR in mind.

Question 64

What is Gene Knock-Out, done using CRISPR

Answer 64

Gene-Knock out:
Gene silencing using CRISPR starts with the use of a single guide RNA to target genes and initiate a double-stranded break using the Ca9 endonuclease; these breaks are then repaired by an innate DNA repair mechanism, the non-homologous end-joining (NHEJ). However, NHEJ is prone to error and can result in genomic deletions or insertions, leading to permanent silencing of the target gene.

Question 65

What are CRISPR Gene Insertions/Knock-ins?

Answer 65

Gene Insertions/Knock-ins:
The CRISPR-induced double-strand break can also create gene-knock-ins by exploiting the cell’s homology-directed repair. The precise insertion of a donor template can alter the coding region of a gene. Previous studies have demonstrated that single-stranded DNA can create exact insertions using the CRISPR-Cas9 system.

Question 66

What is CRISPR Transient Gene Silencing?

Answer 66

Transient Gene silencing:
Modifies the Ca9 protein so it cannot cut DNA; it also allows for gene silencing or transcriptional repression can also be done. The modified Cas9, led by a guide RNA, targets the promotor region of a gene and reduces the transcriptional activity and gene expression.

Question 67

What is Bt? From where was it originally isolated?

Answer 67

Bacillus thuringiensis is what Bt stands for, it is a group of soil microbes that
are used to control certain insect pests.

Question 68

When were the first attempts to use Bt for insect control?

Answer 68

The first attempts to use Bt for insect control were in 1958 when it was first
manufactured commercially and was registered by the US Environmental
Protection Agency in 1961.
- Bt is toxic because it produces a crystal-shaped protein which is a Cry protein
and this is lethal to certain insects

Question 69

Why is Bt toxic? What are Cry proteins? Why are they toxic to insects

Answer 69

Bt is toxic because it produces a crystal-shaped protein, which is a Cry protein
and this is lethal to certain insects
What are Cry proteins?
- Cry proteins are toxic to insects because they are proteolytically activated by
midcut proteases once ingested and bind to specific receptors located in the
cell membrane and result in cell disruption which leads to cell death.

Question 69

How specific is Bt toxin? What type of organisms is it toxic for?

Answer 69

• There are 67 subgroups of Cry proteins which equal more than 500 different
  types of proteins.
• The Bt toxin is specific to Lepidoptera, Coleoptera, Hymenoptera, and
  Diptera. These organisms are different types of worms and caterpillars.

Question 69

What causes the specificity of Cry proteins?

Answer 69

• The alkaline pH in the insects stomach is what activates the Cry protein.

Question 70

Which genes are introduced into plants to make them insect-resistant?
What is the advantage of producing transgenic crops expressing the Cry proteins over spraying the plants?

Answer 70

Maize and cotton genes are used ?
Advantages:
- Increased crop yield
- Does not harm beneficial insects
- Helps prevent molds from entering the plant
- Disadvantages:
- Narrow specificity
- Cry proteins can be unstable

Question 71

What types of crops have been genetically engineered to be insect resistant?

Answer 71

Maize and cotton

The Bt gene has been introduced into plants to make them insect-resistant
- Producing transgenic crops expressing the Cry proteins is more beneficial
than spraying the plants because it reduces the material and application costs
and it kills the insects that are inside the stalk or near the root

Question 72

What are the ecological risks associated with the use of Bt transgenic crops?

Answer 72

The Cry protein being active in the insecticide where as, it is inactive in
the soil, this could expand the specificity that it affects and kill insects that are
not meant to be killed.
- It is not known if the pollen from the genetically modified plant would be able
to have gene flow with the same crop or a similar crop.

Question 73

What are possible causes of resistance in insects to Bt toxin?

Answer 73

Possible cause of resistance in insects to Bt toxin:
- Mutations in the insect that affect the mode of action in Cry proteins

Question 74

What strategy is used to reduce the appearance of insect resistance to Bt toxin?

Answer 74

The “High Dose Refuge Strategy” is used to reduce the appearance of insect
resistance to Bt toxin. This is when they plant a large number on non-Bt
plants by the Bt producing plants so the insects are attracted to the non-Bt
producing plants and then mate with the resistant insects to produce insects
that are not resistant. This works due to the resistant allele being recessive.

Question 75

What is a Ti plasmid? What types of genes are present in Ti plasmids?

Answer 75

TI plasmids include:
T-DNA or transferred DNA, which includes
Repeated sequences at the ends, called
the left and right border, which are
recognized by the bacterial enzymes
encoded by the
vir genes.
Genes that encode enzymes for the
synthesis of auxin and cytokinin, which
when moved into the plant cell
nucleus results in the plant cell
producing these hormones and leading to
cell division and formation of a tumor
of undifferentiated tissue.
Genes that encode the enzymes
involved in the synthesis of opines.
And virulence genes

Question 76

Is the whole Ti plasmid transferred into the plant cell upon transformation?

Answer 76

No. Repeated sequences at the ends, called
the left and right border, which are
recognized by the bacterial enzymes
encoded by the
vir genes. The plasmid
will be cut at these sequences, and all
the DNA in between will be
transferred to the plant cell nucleus

Question 77

What is the T-DNA? What types of genes are present in the T-DNA? What sequences are recognized in the T-DNA by the virulence proteins?

Answer 77

T-DNA or transferred DNA, which includes
Repeated sequences at the ends, called
the left and right border, which are
recognized by the bacterial enzymes
encoded by the
vir genes.

Question 78

What is the starch-statolith hypothesis? What evidence supports this hypothesis? Does this hypothesis explain gravitropism completely? Why?

Answer 78

Starch-Statolith Hypothesis
* Says that the primary mechanism for plants to sense gravistimulation is amyloplast
sedimentation
* This sedimentation activates a receptor, triggering a signal pathway that promotes
gravitropic curvature

Evidence
* Physiological treatments that alter the starch content
* Result in decreased amyloplast sedimentation and gravitropic response

• Starch-deficient / starchless mutants have poor response to gravistimulation
• Scarecrow & shortroot Arabidopsis mutants result in the endodermal layer
  disappearing in both shoots and roots
• Root cap structure is not altered and roots can still respond to gravistimulation
  This theory does not fully explain gravitropism
• Alternative mechanisms possible

Question 79

What could be an alternative sensing mechanism of gravity to the one proposed in the starch-statolith hypothesis?

Answer 79

Evidence suggesting it is not solely
amyloplast sedimentation
* Starch sufficient mutants not completely
agravitropic
Full ablation of Arabidopsis root caps does not
fully inhibit gravitropism
* Is another mechanism causing this?
Possible other mechanism
* Cellular device that senses tension between
the extracellular matrix

Question 80

Which molecules/ions appear to work as second messengers in gravitropism?

Answer 80

Suspected messengers for communication
* Calcium and inositol-1,4,5-trisphosphate
Researchers propose involvement of calcium
channels in signal transduction
* Columella amyloplasts attached to
microfilaments that are connected to the ER or
plasma membrane, and have high calcium concentration.
Not a lot of evidence tho

Evidence of IP3 involvement
* IP3 levels fluctuate in
gravistimulated corn and oat
pulvini
* Rapid changes of IP3 levels
within 10 seconds of
gravistimulation
* IP3 promotes opening
calcium gates

Question 81

What is the Cholodny-Went theory? According to this theory what generates the differential rate of elongation on opposite sides of the root and therefore curvature of the root?

Answer 81

What is it?
* Gravistimulation promotes
development of auxin
gradient across root tip
Cellular Elongation
* Auxin gradient causes
differential rate of cellular
elongation
* Caused by change in
distribution of auxin efflux
facilitators
* Leads to root curvature

Question 82

What evidence do we have that auxin is involved in gravitropism?

Answer 82

Polar Transport is essential for root gravitropism
* Inhibitors of polar auxin transport completely
inhibit gravitropism
* Mutations that affect auxin transport also affect
gravitropism
* Arabidopsis AUXI gene appears to function in
auxin intake
* Mutations in this gene causes root-growth
resistance in two auxin types that actively
diffuses, but does not cause root-growth
resistance in the only auxin type that diffuses
freely
Arabidopsis AGRI gene essential for root gravitropism
* Mutant roots less sensitive t

Question 83

Does an increase in auxin concentration have the same effect on shoot and root cells? Compare phototropism and gravitropism.

Answer 83

increases in auxin concentration
* Affect roots and shoots differently
Roots
* Auxin increase inhibits cellular elongation in
root
* Most likely because root cells are exposed to
resting auxin levels normally
Shoots
* Auxin IAA synthesized in shoot apex
* Regulates cell expansion by activating ATPase

Asymmetrical distribution in the root
* Affects the root elongation zone
* Increased auxin levels transported
to lower side of the root

Question 84

In which part of the root does the asymmetrical auxin distribution have an effect?

Answer 84

Elongation zone

Question 85

Do we know how gravity results in the asymmetrical distribution of the PIN proteins (auxin efflux carriers) and auxin redistribution?

Answer 85

Gravistimulation results in redistribution
of PIN proteins to the bottom flanks of cells
* Also results in:
* fast alkalinization of cytoplasm
* Change of cellular polarity