Plant Adaptations Flashcards
shoot growth
- apical meristems (populations of totipotent cells at the tip of each stem and branch) is where growth is initiated
- meristem cells divide and are found in auxiliary buds (remain dormant until triggered to grow) near shoot tips
- cells below meristems do not divide, they elongate
- leaf primordia are umps on the meristems that become leaves (branching)
photoreceptors
sense availability of light
mechanical receptors
sense physical influences such as gravity and wind
chemical receptors
detect the presence of chemicals and chemical gradients
receptors…
change metabolism or gene expression
tropism
bending or turning of an organism in response to an external signal
phototropism
bending in response to light - auxins accumulate in the shaded side so it grows faster and bends
- positive phototropism: stems towards light
- negative: roots move away from light - auxin produces ethylene which reduces elongation - bends away
gravitropism
bending in response to gravity - starch sinks to the bottom of cells, presses on cytoskeleton and membranes producing auxin - bent up in leaves and down in roots
positive - roots grow down with gravity
negative - stems up, against gravity
statolith
starch-filled organelles in root caps that sense gravity. - heavy statocyst in animals
sees can delay germination if they detect plants overhead
leaves absorb red wavelength but not far red light - passes to seeds below. red light triggers germination, far red light inhibits it
phytochrome
a photoreceptors for red and far red light that switches back and forth between two stable forms, active and inactive, depending on light
- red = Pfr = active and seeds germinate
- far red = Pfr becomes Pr = inactive form (activated again by red light)
- Pfr converts to Pr slowly in the dark
plants grow taller and branch less when in the shade of other plants
seeds that germinate in the dark produce white seedlings with elongated internodes and small leaves - resources into getting tall and reaching light
- in light, intermodal elongation slows and leaves expand
- plants above absorb red light and only far red light goes to seed
roots elongate more and branch less when water is scarce
- root cap senses water
- in dry soil, root cap cells produce abscisic acid - roots elongate, stomata close and seeds remain dormant
- abscisic acid surpasses ethylene synthesis (slows root elongation, influences orientation of cellulose in cell wall)
exposure to wind results in shorter and stronger stems
tough sensitive genes activated by mechanical perturbation
- produce more ethylene when moved - expand in diameter; shorter, thicker
timing of developmental events
important to respond to seasons and temperature is unreliable. day length is used
photoperiodism
the effect of photoperiod or daylight on flowering
short day plant
a plant that flowers only when the day is shorter than a critical value (late summer)
long day plants
opposite, so midsummer
day-neutral plants
independent of day length
- allows for plants to flower only when they have resources to support seeds and for seeds to have enough time to mature before winter
circadian clock and photoreceptors
- circadian clocks let the plant know how long it has been since the sun came up (affects transcription)
- phytochrome detects dark and light
plasmodesmata
connection between the plasma membranes of adjacent plant cells that permit molecules to pass directly from the cytoplasm of one cell to that of another - chemical signals and pathogens are also moved
xylem
vascular tissue consisting of lignified conduits that that transport nutrients and water from the roots to the leaves
- parisites in xylem get access to water and nutrients
- evaporation from leaves, draws water from the soil
- hydrogen bonds pull water
phloem
the vascular tissue that transports carbohydrates from leaves (source) to the rest of the plant (sink)
pathogens
viruses, bacteria, fungi, nematode words and other plants
- fungi spread by growing through cell walls - move (like bacteria) in xylem
- viruses move through plasmodesmata and phloem
first line of defence
epidermis (thick walls with waxy cuticle) is the first line of defence
- pathogens enter through wounds or by piercing walls (nematodes)
- enter through stomata
- enzymes weaken walls
biotropic pathogen
obtains resources from living cells - viruses, bacteria and fungi
necrotropic pathogen
kills cells before drawing resources from them - bacteria and fungi
parasitic plants
infect other plants through vascular system to get resources
host plants
infected by a pathogen - not always damaged much
virulent
a pathogen that overcame defences and lead to disease
avirulent
pathogens only damage a small part - can contain disease
immune system
protein receptors bind to pathogenic molecules and recognise them - cascade leads to response
basal resistance
receptor proteins in plants plasma membrane binds to pathogen molecules
defense response is triggered
specific resistance
deal with pathogens that survive basal resistance
- pathogens secrete AVR proteins that enter plant cells and might block defence
- R proteins (resistance receptors) are specific to each AVR
- absence of specific R - AVR blocks basal
- binding prevents AVR from blocking and activates defence system
- race to evolve AVR and R - which is faster?
hypersensitive response
uninfected cells surrounding infection produce large numbers of reactive oxygen species, triggering cell wall reinforcement and causing cells to die, creating a barrier
prevents spread of biotropic pathogens
other ways to block pathogens
plug xylem
mechanical and chemical defence against herbivores
hairs, latex (white sticky light that glues mouth parts and is toxic), chemical irritants, silica plates in epidermal cells wear mouthparts, prickles, spines
chemical compounds
- cardenolides
- alkaloids - nitrogen bearing compounds that damage NS and are bitter (caffeine)
- terpene - defence compounds that do not contain nitrogen (for proteins), volatile and vaporising (oils), deter herbivores and obstruct growth and metabolism of fungi and insects
- phenols - tannins (bind to proteins and reduce digestibility, don’t taste good)
- non-protein amino acids cause insects to grow slowly and die
- protease inhibitor - antidigestive protein that binds to enzymes in the herbivore’s digestive system
grasses regrow quickly
apical meristem close to the ground to avoid damage and can grow leaves when bitten
allocating resources for defence
to preserve resources, some defences can be turned on when needed (inducible)
recognise the pathogen and respond only when present
produce volatile signals that attract insects to prey upon herbivores
nutrient rich environments select for plants that allocate resources to growth than defence - can afford to replace and heal if damaged (trade off)
