Ch. 32 Plant Defense and Behavior Flashcards
what is a plant’s first line of defense against pathogens?
epidermis (thick walls and waxy cuticle)
how do pathogens most commonly enter the plant?
they cannot penetrate the cuticle, so they enter through:
- wounds
- piercing mouthparts of insects/nematodes
- stomata
how do pathogens spread throughout the plant once inside?
they use existing transport proteins
define biotrophic pathogens
pathogens that obtain resources form living cells
define necrotrophic pathogens
pathogens that kill cells before colonizing them
what type of pathogen is a virus?
biotrophic
what are parasitic plants?
plants that obtain resources by infecting other plants and tapping into their host plant’s vascular system
what are heteroparasites?
Parasitic plants, tap into the host plant’s tissue to retrieve water and minerals (mistletoe)
what are holoparasites?
Parasitic plants, tap into the host plant’s tissue to retrieve water and minerals AND also sugars (cuscuta and rafflesia)
define virulent pathogen
pathogens that are able to overcome the host plant’s defenses and lead to disease
define avirulent pathogen
pathogens that damage only a small part of the host plant because the host is able to contain the infection
what are the two parts of a plant immune system?
- basal (general)
2. specific
what are characteristics of the basal immune system?
- plasma membrane receptors recognize molecules produced by broad classes of pathogens
- “first line of defense”
what are characteristics of the specific immune system?
- depends on R genes
- allow plant cells to identify and deactivate AVR proteins produced by specific pathogens
- directly activates defensive genes
- described as the “arms race” because AVR proteins get smarter and R proteins must also get smarter to be able to keep defending the plant
define “R” proteins
- receptors on cell membranes that detect pathogens
- each is coded by an R gene (resistance)
define AVR proteins
- avirulence proteins
- produced by pathogens
- enter into plant cells and facilitate infection
what happens when an specific R protein binds with a specific AVR protein?
- prevents AVR protein from blocking the plant’s defenses
2. activates additional defenses
define hypersensitive response
- uninfected cells surrounding the infection rapidly produce large numbers of oxygen reactive species
- triggers wall reinforcements and causes cells to die
- death of surrounding dead cells = barrier of dead tissue
- blocks biotrophic pathogens and slows the growth of necrotrophic pathogens
define a chemical response
plant produces antimicrobial compounds that attack bacterial/fungal cell walls
define a physical response
strengthening cell walls, plugging xylem, closing stomata
define vascular wilt disease
- sometimes leads to plant suicide
- can occur when plant defenses end up blocking water sources to leaves (blocking xylem)
define systematic acquired resistance (SAR)
- acquired immunity
- ability to resist future infections
(ex. healthy tobacco leaves can acquire resistance to a pathogen if other leaves on the same plant have already been exposed) - occurs in response to a wide range of pathogens ONLY when an infection results in necrosis (vascular wilt disease or hypersensitive response)
can pathogens alter genomes?
YES! some bacteria have found a way to insert some of their genome into the host cell and trigger a certain behavior in the host cell
(ex. Rhizobium radiobacter)
what happens usually when bacteria insert a Ti plasma of their own DNA into the host cells genome?
- Ti genes cause host cells to divide
- a tumor forms
- cells produce compounds that the bacteria can metabolize
how do caterpillars overcome the chemical defense of milkweed leaves?
- they “dig trenches”
- larger caterpillars sever major veins and block toxic “latex” flow
- milkweed leaves also have a mechanical defense (many hairs)
what are some examples of mechanical defenses?
- spines (on stems and branches)
- hairs (some hairs secrete chemical defenses, too)
characteristics of chemical defenses (alkaloids)
- nitrogen bearing compounds (very costly)
- damage nervous system of animals
- bitter tasting
- (ex. caffeine, morphine, nicotine)
- very effective in small concentrations
characteristics of chemical defenses (terpenes)
- do not contain nitrogen
- volatile/evaporate easily
- make up many of the essential oils of plants
- spread easily
- may serve as warning signals/strong smell/imitate insect hormones
characteristics of chemical defenses (phenols)
- (tannins)
- bind to proteins and reduce digestibility of the plants (make them less easy to eat)
define protease inhibitors
defensive proteins that bind to the active site of enzymes in the herbivore’s digestive system
- reduces the nutritional value of plant tissue
- keeps proteins from being broken down
what is a very common example of a biotic defender? what is the cost of employing this defender?
- ants
- cost = nectar
- removing ants leads to higher herbivory
what are myrmecophiles?
- ant plants
- provide food and shelter to plants
- plants emit chemical that repels ants away from flowers so that other pollinators can still be involved
how are grasses adapted to protect themselves from predation?
- apical meristems are close to the ground (they wont get bitten off)
- leaves tightly imbricated
- leaves grow from the base
define constitutive defense
defenses that are always active
-occurs when a threat is constant or generalized
define inducible defense
defenses that are only active when the plant senses a threat
-occurs when threat is uncommon
what happens when a plant is attacked by herbivores?
- it expresses a new set of genes
- genes increase production of chemical defenses, strengthen cell walls, and trigger production of jasmonic acid
define jasmonic acid. what does it ultimately do?
- production is triggered when a plant is attacked by herbivores
- signal that is transmitted through the phloem
- induces transcription of defensive genes
- volatile chemicals released from damaged plants trigger defensive response in undamaged plants*
what is the janzen-connell hypothesis?
Vulnerability of a population to
disease is dependent on the
density of its individuals.
Many, low-density species are
more likely to survive than a
few, high-density species.
Dispersal of seeds is critical not simply to reduce competition between generations but also to reduce exposure of the offspring to pathogens.
how do we protect crops from herbivores and pathogens?
- Applying pesticides/herbicides
- Understanding the ecology of the farm
- Crop breeding
