plant hormones Flashcards
in what way does a plant grow?
toward light
phototropism
the growth of a shoot toward light
what side of the plant is longer?
darker side longer than lighter side
actively dividing tips of roots and shoots
apical meristem
what do the different growth rates allow for?
allow apical meristem to bend toward light
what happened to the grass seedling when the tip was removed?
the shoot grew straight and wouldnt bend toward the light
what happened to the grass seedling when the tip was covered with an opaque top?
grew straight
what happened to the grass seedling when the tip was covered with a transparent cap?
grew toward light
what happened to the grass seedling when the base was covered with opaque shield?
grew toward light
what happened to the grass seedling when the tip was separated by permeable gelatin block?
grew toward light
what happened to the grass seedling when the tip was separated by impermeable mica??
grew straight
what happened when the tip was cut and placed in a block of agar?
chemical messenger/hormone diffused form the tip into the agar
what was done with the agar?
used as a substitute into the different “tipless” plants and grown in the dark to test the chemical only and not the sunlight
what was the result of the agar test?
shoots grow toward the light because of a greater concentration of auxin
auxin
growth promoting chemical on the dark side of the shoot
gravitropism
if a seeding is placed on its side, shoot bends upward and the root curves downward
hypothesis for gravitropism
settling of statoliths- organelles containing heavy/dense starch – and an uneven distribution of it may turn signal the cell to redistribute auxins
thigmotropism
long lasting growth movement in response to touch - ivy and climbing plants
how does a plant’s hormones work?
made in one part of the organisms and influences cells at another part and can pass through all walls and alter plant physiology
5 main classes of hormones
Auxin
Cytokinin
Gibberellins (GA)
Abscisic Acid (ABA)
Ethylene
what do auxins do?
ex.IAA (indoleacetic acid)
promotes growth by cell elongation primarily in the shoots of the plants- apical meristem
when does IAA promote growth?
at a certain concentration, and if it gets too high ethylene is made to inhibit it
how does auxin makes plant cells elongate?
by increasing the H+ inside primary cell walls, which then activate enzymes that break bonds of the cellulose in cell walls. Cell swells with water and elongates as the cell wall no longer resists the cell’s tendency to take up water osmotically. cell stays bigger synthesizing more cell wall material (cellulose) and cytosol
what do cytokinins do?
promote cell division
where are cytokinins found?
actively growing tissues, especially in the roots, which may be transported throughout the plant to other target tissues
what do cytokinins slow?
senescence - aging of flowers and fruits
how do cytokinins influence organogenesis?
cytokinins and auxins can influence whether a plant is tall or wide
auxin : if terminal bud is attached, auxin travels down the stem and allows the stem to elongate, inhibiting auxillary side branches
cytokinins: if terminal bud is removed, no auxin is there to elongate stem and inhibit side branches, so cytokinins transported from roots to activate the side auxillary buds and plant grew bushy
what are Gibberellins (GA)?
plant hormones made at the tip of roots and shoots
main effect of GA?
elongation in stems and leaves
bolting
high concentration of GA causes rapid elongation of stems which enhances the effects of auxins
combined with auxin, what do GA influence?
fruit development - spraying them with this makes them develop w/o fertilization such as seedless grapes
what do GA cause in seed germination?
cause a seed to sprout when sprayed onto seeds
what does abscisic acid do?
when it’s necessary for a plant to be dormant in winters or sever droughts, it becomes produced in the buds and signals the bud to form scaled that will protect them from harsh conditions
what does ABA inhibit?
it is a growth inhibitor and causes seeds to remain dormant
how to get rid of ABA?
when rain washed ABA out of the seeds
what ratio determines if a seed sprouts or remains dormant?
ratio of ABA and GA
how else does ABA act as?
stress hormone - helping them to cope with adverse conditions
how does ABA work if a plant is dehydrated?
accumulates in the leaves causing the stomata to close to prevent transpiration
what does ABA thought to have done?
abscission- breaking off of leaves from trees
what does ethylene do?
triggers fruit ripening
how does fruit ripen?
breakdown of cells walls that cause characteristic color changes
how do farmers slow the action of ethylene?
flushing stored apples with CO2
what happens if a very ripe fruit is placed in a bag with an unripe fruit?
unripe fruit ripens quicker
what else does ethylene do?
plays a role in the fall color changes and drying of leaves and promotes abscission
what rhythmic behavior do plants display?
opening and closing of stomata and sleep movements
circadian rhythm
biological cycle of about 24 hours
what happens to circadian rhythms when an organism is removed from environmental cues?
continue to persist
what are circadian rhythms controlled by?
internal timekeepers called biological clock
biological clock
continues to mark time in the absence of environmental cues, but to remain tuned to a period of exactly 24 hours it needs daily signals from the environmental
what happens to a plant’s sleep movements if kept in constant darkness?
change slightly to a cycle of about 26 hours
what is a biological clock?
not sure in plants- but in humans the clock is a cluster of nerve cells in the pineal gland that makes melatonin
what are biological clocks and circadian rhythms they control not affected by?
temperature shifts
what does a biological clock influence besides a plant’s daily activites?
seasonal events- flowering, seed germination, and the onset and ending of dormancy
what is the environmental stimulus plants most often use to detect the time of the year?
photoperiod - the relative lengths of night and day
2 groups that are triggered by photoperiod
long night
short night
short day/long night plants
plants flower in the late summer, fall, or winter when there is little sunlight and long nights
ex. poinsettias
long day/short night plants
plants flower in the late spring or early summer
ex. spinach, lettuce, iris
when do spinach flower?
10 hours of consecutive hours of darkness, and if this is interrupted by a single flash of light, it will not flower
what does flowering and other responses depend on?
night length
critical period
how much night a plant needs to flower
how to plants measure photoperiod/night length?
aid of phytochromes - a colored protein that absorbs wavelength of red light
red light - R
wavelength 660nm
interrupts
far red light - FR
wavelength 730 nm
corrects regardless of the number of R light flashes as long as it is the last flash
what does phytochrome alternate between?
Pr and Pfr
Pr
absorbs red light
fr
absorbs far red light
how quick is this conversion?
very fast
what do plants make?
Pr
if a plant remains in the dark, what form is the pigment in? sunrise? sunset?
Pr; Pfr; Pr
this sets the plant’s biological clock
this biological clock measures?
the time between the conversion of these 2 forms, or the time from sunset to sunrise
what does phytochrome do?
tells time of day and the season
what does Pfr do?
triggers Reponses such as seed germination, flowering, and stomata opening
