Biotic Interactions Flashcards
Define mutualism
a symbiotic relationship in which both organisms benefit
Define herbivory
consumption of plants or parts of plants as a food source
Define microbial pathogens
bacterial or fungal organisms that cause disease in a host plant
Define parasites
an organism that lives on or in a host, from which the parasite obtains nutrients
Define allelopathy
release of substances that have harmful effects on neighboring plants
Define coevolution
linking adaptations of two or more organisms
Define commensalism
relationship between two organisms in which one organism benefits without negatively affecting the other
What is the first line of defense against harm and what is the second line of defense in plants
first = plant surface (cuticle, periderm)
second = biochemical mechanisms
Define biochemical mechanisms as either constitutive or inducible defenses
constitutive = are always on/present so are immediately available
inducible = exist at a low level until a stress is encountered and trigger an attack. they require detection systems
what caused the emergence of the first land plants
symbiotic associations between marine algae and fungi
What microorganisms can cause diseases in plants
fungi, oomycetes, bacteria and viruses
Define nod factors
they are receptors that are signaling molecules in the symbiotic interaction between legumes and rhizobia involved in plant defense related perception
explain what plant roots provide and what plants provide
plant roots provide nutrient rich habitat while the plant provides exudates (sugars) in exchange for beneficial services
What do the majority of plant fungal pathogens belong to
ascomycetes (produce spores inside saclike ascus) and basidiomycetes (produce spores outside basidia cells)
What fungi-like organisms caused potato late blight and led to irish potato famine
oomycetes that include some of the most destructive plant pathogens in history
What are 3 ways/categories that plants have evolved mechanisms to defend themselves against herbivory of insects
- mechanical barriers
- constitutive chemical defenses
- direct/indirect inducible defenses
What evidence suggests that the majority of plant-herbivore interactions have involved co-evolution
90% of insect herbivores are restricted to single family of plants (specialists) and only 10% are generalists
Define mechanical barriers and examples
first line of defense against insect pests and pathogens
ex. surface structure (thorns, spines, prickles), touch-induced leaf movement, mineral crystals,
Define thorns
modified branches, sharp structures that physically deter herbivores
ex. russian olive trees
Define spines
stiff plant structures, modified leaves, can assist in water conservation and physically deter herbivore
ex. cacti
Define prickles
pointed plant structures derived from epidermal cells and easily snapped off the stems
Define trichomes
unicellular or multicellular hairlike structures from epidermal cells of shoots and roots that provide defense against insect pests by physical and chemical defenses
Define glandular trichomes
store species-specific secondary metabolites in a pocket between the cell wall and cuticle that burst and release contents because of contact with a strong bitter smell and taste which repel insect herbivores
Explain how leaves of stinging nettle have effective barriers against herbivores
they have specialized stinging hairs that are needlelike trichomes reinforced with glass silicates filled with a mixture of acids and liquids that cause severe irritation and inflammation
the tip snaps off with touch and is sharp which pushes trichome down and is a syringe that plunges down and injects chemicals into skin
How can trichomes act as herbivore sensors
when bent or damaged they send electrical or chemical signals to surrounding cells which can signal inducible defense compounds
explain phytoliths
a mineral crystal - silica crystals (phytoliths) in cell walls and vacuoles that add toughness and make it difficult to chew, a mechanical barrier
calcium oxolate crystals
in vacuoles, a mineral crystal, that form bunches of needlelike structures = raphides, a mechanical barrier
Explain the mechanical barriers in Mimosa
sensitive plant, they have pulvinus joint like structures that cause folding in response to heat, touch, damage, etc.
ex. fast folding/collapses cause startling
Define primary metabolites
compounds that all plants produce and are directly involved in growth and development, involved in second line of defense
Define secondary metabolites
species-specific, derived from modification pathways that also produce plant hormones and secondary cell wall components, involved in secondary line of defense
Define phytoalexins
secondary metabolites with strong antimicrobial activities that accumulate around infection sites
Examples of plants that are toxic to humans
hemlock and foxglove
How to avoid toxicity and accumulation of secondarily metabolites in the plant itself
they must safely store in cellular compartments isolated from susceptible tissues (vacuoles, resin ducts, laticifers, or glandular trichomes)
Define resin
are released from conifers that can be toxic to an attacking insect or act as adhesive to glue mouthparts together or engulf the whole insect, example of chemical defense
Define laticifers and examples of plants that do so
composed of cells that produce a milky fluid of latex that coagulate (change to solid or semi-solid) upon exposure to air, a chemical defense
opium poppy, milkweed
plants store defensive chemicals as nontoxic in vacuoles, how do they become active
and how is uncontrolled activation prevented
the glycosidic linkages need to be hydrolyzed
prevented by the spatial separation of activating hydrolases and the toxic substrates
how do humans tend to use plants that produce constitutive secondary metabolites
medicinal properties or culinary flavours (spices)
What are the 3 ways insect herbivores can be categorized based on their feeding behaviours
- phloem feeders
- cell-content feeders (piercing and sucking)
- chewing insects
What 2 steps does plant response to insect herbivores involve
- wound response
- recognition of compounds in saliva (effectors that trigger defense response)
the first elicitor (compound in saliva that triggers defense response) identified was
volicitin
explain the coevolution of plants and insect herbivores
both are evolving to overcome barriers to eat or prevent being eaten
chewing and piercing/sucking insects inflict activation of what signaling pathway compared to phloem feeders
chewing +piercing = jasmonic acid/ethylene production
phloem feeders = salicylic acid
elicitors trigger a signal transduction pathway and results in what
an increase in cytosolic Ca concentration
Jasmonates initiates the production of what that inhibit herbivore digestion
defense proteins
Explain inducible defense in response to insect herbivory
induction and release of volatile organic compounds have 3 major pathways - terpenoids, alkaloids, and phenolics.
can also release this volatile compounds to attract natural enemies of herbivores
what are the 4 strategies of pathogens to invade hosts
penetrate cuticle and cell wall by lytic enzymes
enter through natural openings
invade wound sites
transfer by insect vectors
what are the 3 different attack strategies of pathogens once inside a host
- necrotrophic (attack by secreting cell wall degrading enzymes that will kill the affected plant area and eat dead tissue)
- biotrophic (most tissue stays alive with minimal damage and feed on substrates from host)
- hemibiotrophic (initial biotrophic then necrotrophic)
Define effectors
molecules that change plant structures metabolism or hormonal regulation to the advantage of the pathogen, support ability of pathogen to colonize
What are the 3 classes of effectors, briefly explain each
- enzymes (degrade wall and cuticle)
- toxins (target specific proteins of plants)
- growth regulators (interfere with hormonal balance)
Define PRRs and MAMPs
pattern recognition receptors that set off defense response that is activated by the binding of microbe-associated molecular patterns
Define hypersensitive response
the surrounding cells around infected site rapidly die to prevent the spread, plant defense against pathogen
define systemic acquired resistance
plants that survive infection, develop increased resistance called SAR
Define nematodes
parasites that rely on others to complete their lifestyles and feed through hollow stylet that penetrates plant cell walls
What are the 2 types of nematodes and explain each
- cyst = form specific feeding structure, female cyst nematode dies, then forms a cyst containing fertilized eggs which new juveniles will hatch
- root-knot = formation of giant cells that female nematode releases egg mass with maturation and produce more juveniles
what are the 2 types of parasitic plants, explain each
hemiparasites = facultative parasites that can still perform some photosynthesis processes
holoparasites = obligate parasites that cannot perform any photosynthesis
define haustorium
specialized structure of parasitic plants to penetrate hosts and absorb nutrients from
