Plant Responses Flashcards
what is abiotic stress
non living environmental factors that affect plant
how do plants respond to abiotic stress and herbivory
may produce anti freeze enzymes
may be bitter tasting
release cell signalling pheromones to trigger defensive responses in other organisms
what is a plant tropism. with examples
directional growth response of a plant
phototropism-growth towards light
geotropism-growth towards gravity
hydrotropism-response to water
thermotropism-response to temperature
thigmotropism-response to touch
how is leaf abscission (loss) controlled in deciduous plants controlled
as leaf ages, cytokine and auxin levels lower, ethene levels increase
triggers production of cellulase enzymes -weaken leaves by breaking down cell wall in abscission layer
leaves break from branch
what are the functions of gibberellins
germination
elongation at cell internodes
fruit growth
rapid growth/flowering
how is germination stimulated
seed absorbs water , activating embryo to secrete gibberellins
gibberellins diffuse into aleurone layer-producing amylase
amylase diffuses into endosperm layer to hydrolyse starch
hexose sugars act as respiratory substrates to produce ATP
what are the functions of auxin
involved in trophic response
control cell elongation
suppress lateral buds to maintain apical dominance
promote root growth
explain how shoots show positive phototropism
indoleacetic acid diffuses to shaded side
causes active transport of H+ ions into cell walls
disruption of H bonds between cellulose molecules and expansion make cell more permeable to water
cells on shaded side elongate faster due to turgor pressures
shoot bends towards light
explain why roots show positive geotropism
gravity causes IAA to accumulate on lower side of root
IAA inhibits elongation of root cell
cells on upper side elongate faster so root tip bends downwards
how do hormones stimulate stomata to open/close
abscisic acid binds to complementary receptors on guard cell membrane causing Ca channels to open-diffuses from vacuole to cytosol
positive feedback triggers other ion channels to open
water potential of guard cell becomes more positive-water diffuses out
guard cells become flaccid so stomata close
what is apical dominance
during growth of shoot, the side shoots do not grow
explain the evidence that auxins maintain apical dominance
auxin in apex maintains high levels of abscisic acid-promotes side shoot growth
explain the evidence that gibberellins control germination and elongation
stem elongation-tall plants have higher gibberellin concentrations
germination-seeds with non functional germination gene do not germinate unless gibberellin inserted externally
how are auxins used commercially
rooting powder
growing seedless fruit
high concentrations promote fruit drop
how are cytokines used commercially
prevent yellowing of lettuce leaves
promotes shoot growth
