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Lecture 16

BIOL103 Lecture 16: Week 6, Lectures 16-18


Department
Biology
Course Code
BIOL 103
Professor
Virginia K Walker
Lecture
16

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Week 6
Immunity in other systems: plants
Both general and specific responses
Defense against virus, bacteria, fungi, nematodes, protists and fungi
Classic experiments by A.F. Ross infecting tobacco plants with tobacco mosaic virus
• A$er 2 weeks only 1 leaf had died, R receptors
Plant immune systems work intercellularly and intracellularly
Have airborne signals, allows them to communicate with other plants
What about insects?
Hemolymph
Insect blood
90% plasma
Amino acids
Sugars
Ions
Proteins
Hormones
10% cells
• Hemocytes
Make cell fragments
~70 000/mm3 but this is less than 5M red blood cells and 7000 white
blood cells in human blood
Phagocytosis
• Non-specific
First bacteria phagocytotic cells will also respond to other bacteria
and recognize them
Inject an insect with bacteria to increase number of phagocytotic cells
Encapsulation
Clotting
Not regulated
Notes:
Except rarely, oxygen is carried by the tracheal system, not by proteins in the
hemolymph
Classification of insect hemocytes is an issue that stimulates an instantaneous loss of
good manners and an induction of bad temper at any conference on insect
physiology or immunity
If there is a cut in an insect hemocytes break open and release cytoplasmic contents, a so$
clot forms that involves Ca++ and phenyloxidase, which releases melanin - bacteria
stimulates phenyloxidase, which increases melanin, which increases so$ clots
Insect Immunity
Encapsulation of parasites or other foreign materials (photo in notes)
Parasites eat insect from the inside out?
Hemocyte recognizes egg as foreign material
It becomes covered in melanin, which prevents 02 from going into the egg, which
causes the egg to die and prevent the parasite from killing the insect

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Insect immunity: innate immunity and very eective
!
Fat body - immune tissues found in the liver
Receptors (Toll, peptidylglycan recognition proteins, etc.) on the hemocytes and fat
body initiate signal transduction events - which leads to activation of mediators such
as kinases - which results in the production of eectors such as antimicrobial
peptides, virus induced RNA and thioester containing proteins, etc.
If there is a virus, an antibacterial protein would not be produced - if there was a
bacteria, an antiviral protein would not be produced
Endocrine systems: hormones and chemical controls
Rhodnius or “the kissing bug” can transmit trypanosomes that can cause Chagas
disease, it is important in the history of hormone research
Chagas Disease: Life cycle
!
Parasite remains in the belly
The trypanosome parasites can “change” their glycoprotein coats and
therefore try to evade the immune system
Enter humans through the mouth and drink blood from the lips, they
defecate while taking blood so the feces gets rubbed into the cuts from
biting them to drink blood so humans become infected
Sir Vincent Wigglesworth had important experiments on these insects
Nymphs usually become adults a$er 28 days a$er consuming a blood meal
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First Experiment: 1 day a$er blood meal, he chopped the nymph’s head o,
waited and waited, still was a nymph and did not molt - so suggests that a
head and blood meal are required to molt
Second Experiment: 8 days a$er blood meal, chopped o head, waited 20
days, became an adult - so suggests that a blood meal and a head were
needed for some period of time < 8 days to molt
Third Experiment: 1 day a$er blood meal, chopped head o, and took the
bodies of the nymph with no head and the adult with no head from the
second experiment and stuck their bodies together, ~20 days later there
were two adults stuck together with no heads
Regulation of molting in Rhodnius by hormone action
See loose leaf
Regulation of molting during moth development
!
Four Dierent Classes of Hormones
1. Amines
Derived from tyrosine or tryptophan
Examples: dopamine, melatonin
2. Peptide hormones
Example: prolactin, but can also include larger proteins
3. Steroids
Cholesterol derivatives
Less soluble in water
4. Others
• Examples:
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