Flashcards in Ch. 32 Plant Defense and Behavior Deck (39)
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:
2. piercing mouthparts of insects/nematodes
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?
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?
1. basal (general)
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
-produced by pathogens
-enter into plant cells and facilitate infection
what happens when an specific R protein binds with a specific AVR protein?
1. 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)
-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
-(ex. caffeine, morphine, nicotine)
-very effective in small concentrations
characteristics of chemical defenses (terpenes)
-do not contain nitrogen
-make up many of the essential oils of plants
-may serve as warning signals/strong smell/imitate insect hormones
characteristics of chemical defenses (phenols)
-bind to proteins and reduce digestibility of the plants (make them less easy to eat)