16.2 Plant responses to abiotic stress Flashcards
what is an abiotic stress?
any non-living factor which is potentially harmful to a natural plant
how does falling light affect auxin concentrations?
auxin concentrations also fall
how do leaves respond to a fall in auxin concentration?
they produce ethene
a gas
relationship between auxin and ethene
antagonistic
outline leaf fall
ethene switches on genes in the walls of the abscission zone which leads to the production of enzymes which digest and weaken the cell wall in the separation layer
vascular bundle is sealed off to prevent material from leaving
a fatty layer is deposited which acts as a protective layer by preventing pathogens from reaching the vascular bundle
cells in the separation zone swell and then under a biotic pressure, such as wind, the leaf falls off
why is leaf loss important for the winter?
helps plants conserve water by preventing water loss
soil water might be frozen
why is it important for plants not to freeze?
when cells freeze, their membranes get disrupted and they will end up dying
how do plant cells prevent freezing?
antifreeze proteins are produced by the plant at low temperatures
these proteins bind to ice crystals and prevent them from growing
what is the stomata open for?
to cool the plant as water evaporates from the cells
what is the stomata closed for?
to prevent water loss
what opens and closes the stomata?
guard cells
flaccid = closed
turgid = open
which hormone triggers stomatal closure?
ABA
how does ABA work to close the stomata?
ABA binds to receptors on the guard cell membrane
ABA causes the ion channels to open which allow Ca2+ ions into the cytosol
this Ca 2+ causes other ion channels to open which means K+ ions leave the cytosol
this creates a higher water potential in the cytosol which means water moves out of the guard cell by osmosis
leads to the guard cells becoming flaccid
so now closed
