Plant Defenses Flashcards
Factors that threaten plants
weather, fire, viruses, bacteria, fungi, animals, and other plants
What is the first line of defense in plants
dermal tissue system
Epidermal cells
Dermal tissue system
secrete wax to protect plant surfaces from water loss and attack
cutin
dermal tissue system
above-ground parts also covered with cutin
Suberin
dermal tissue system
Found in cell walls of subterranean plant organs
Other parts of the dermal tissue system
silica inclusions, trichomes, bark, and even thorns
what allows microbial entry
mechanical wounds
Parasitic nematodes
use their sharp mouth parts to get through the plant cell walls
Some form tumors on roots
what can increase the risk of frost damage
having bacteria on the leaf
How do fungi invade
seek out the weak spot in the dermal system, or stomata, to enter the plant
Phases of fungal invasion
- Windblown spore lands on leaves
- Spore germinates and forms adhesion pad
- Hyphae grow through the cell walls and press against cell membrane
- Hyphae differentiate into haustoria
Why are beetles dangerous
they transport fungi in their mouthparts
Blue stain fungi
various species of fungi Not closely related to eachother Fungus in sapwood stops pitch flow - blocking tree from repelling beetles Cuts water and nutrient flow Fungus serves as food for larvae
Beneficial fungi and bacteria
Mycorrhizal fungi
Nitrogen-fixing bacteria like Rhizobium
Plant growth-promoting rhizobia (PGR
Plant growth-promoting rhizobia (PGR)
Bacteria provide substances that support plant growth
Can also limit the growth of pathogenic soil bacteria
Defensins
Chemical Defense
found in plants and animals
small, cysteine-rich peptides with antimicrobial properties
In some cases defenses limit protein synthesis
Secondary metabolites
Alkaloids and Tannins
How can animals avoid the toxic effects of secondary metabolites
by eating a varied diet
What is the effect of secondary metabolites
Metabolic pathways needed to sustain life are modified
Types of secondary metabolites
Manihotoxin (cyanogenic glycoside), Genistein (phytoestrogen), Pacilitaxel (taxol, terpenoid)
Types of alkaloids
Quinine, Morphine
Two ways in which plants protect themselves from toxins
- Sequester a toxin in a membrane-bound structure
- Produce a compound that is not toxic until it is metabolized by attack animal
- Cyanogenic glycosides break down into cyanide when ingested
Allelopathic Plants
Secrete chemicals to block seed germination or inhibit growth of nearby plants
This strategy minimizes competition for resources
Very little vegetation grows under a black walnut tree
How did socrates die
after drinking a hemlock extract containing nerve-paralyzing alkaloid
How did Georgi Markov die
assassinated by KBG officers using ricin
A pinhead-sized metal sphere was injected from an umbrella tip into his thigh
Ricin
Alkaloid produced by castor-bean plant (Ricinus communism)
6 times more lethal than cyanide and 2 times as cobra venom
A single seed can kill a small child
Functions as a ribosome-binding protein that inhibits translation
Benefits of secondary metabolites to human health
Phytoestrogens of soy plants
Taxol of Pacific Yew Trees
Quinine of Cinchona trees
Phytoestrogens of soy plants
appear to lower the rate of prostate cancer in Asian males
Questions have been raised about their effects on unborn babies
Babies consuming soy-based formula
Taxol of Pacific Yew trees
fights cancers, especially breast cancer
Quinine of Cinchona trees
effective against malaria, which is caused by four species of Plasmodium
Blocks DNA replication
Also leads to build-up of toxic hemes that poison the parasite
Acacia trees and ants
small armies of ants protect Acacia trees from harmful herbivores
Plants provide ants with food and shelter
Parasitoid wasps, caterpillars, and leaves
as caterpillar chews away, a wound response in the plant leads to release of a volatile compound
Female parasitoid wasp is attracted
Lays fertilized eggs in caterpillar
Eggs hatch and larvae kill caterpillar
Systemic response to invaders
Static plant responses to threats have an energetic downslide
-are maintained in the presence or absence of threat
Energy resources would be conserved if the plant response was inducible
Defenses launched only when needed
Wound response
Occurs when a leaf is chewed or injured
-one outcome leads to rapid production of proteinase inhibitors throughout the plant
Bind to digestive enzymes in the gut of the herbivore
Signaling pathway of wound response involves
jasmonic acid
salicylic acid
Mechanical damage
Wound response signaling
- Wounded leaves produce an 18-amino acid peptide called systemic
- Systemin moves throughout the plant in the phloem
- Cells with receptors produce jasmonic acid
- Jasmonic acid turns on genes for proteinase inhibitor
H.H. Flor’s gene-for-gene hypothesis
Plants have a plant resistance gene (R); pathogens have an virulence gene (ave)
It is the recognition of the gene products that is critical
If binding occurs, plant can mount defenses that keep pathogen avirulent
If no binding occurs, the plant succumbs to disease
Hypersensitive Response
Recognition of the pathogen by the R gene product leads to hypersensitive response
Leads to a very rapid cell death around the site of attack
Also to longer term, whole plant resistance
Rapid cell death
due to hypersensitive response
Seals off the wounded tissue to prevent the pathogen or pest from moving into rest of the plant
Hydrogen peroxide and nitric oxide produced
-May signal cascade of chemical events resulting in localized host cell death
Phytoalexins
antimicrobial chemical defense agents
Systemic Acquired Resistance (SAR)
Systemic response by plants
Several pathways lead to broad-ranging resistance that lasts for a period of days
Long-distance inducer is likely salicylic acid
At the cellular level, jasmonic acid is involved in SAR signaling
SAR allows the plant to respond more quickly to a second attack
