18. Phytohormones - Auxin Flashcards
(31 cards)
hormone
chemical messengers, coordinate cellular functions
what is the difference between animal hormones and plant hormones?
animal: usually very specific hormones that come from one tissue type and act on one tissue type, many many different hormones, only certain cells can make hormones
plant: comparatively few hormones that have more numerous effects, most cells can produce them and can act on most cells
went and thinman:
defined phytohormones
produced in one part and transferred to another, inducing a specific physiological response, coordinates organ activityc
classical plant hormones
auxin
Gibberellins
ethylene
cytokinins
abscisic acid
more newly discovered phytohormones
bassinosteroids, salicylates, strigolactones, jasmonates
1890s: Darwin
goal: studies phototropism
model: covers coleoptiles with a hat
results: finds that they no longer bend towards the light
conclusion: must be some receptor in the tip that senses light and causes movement, defines phototropism
phototropism
orientation of a plant in response to light
positive phototropism
moving towards light
negative phototropism
moving away from light
1913: boysen-jensen
model: cut tip off and put other material between tip and rest of the coleoptile (agar, butter, rock, nothing), shielded bottom half
results: only the agar and control bent
conclusion: the compound that is involved in phototropism is water-soluble
1919: paal
model: cut the tips off coleoptiles and put them back on asymmetrically under uniform light
results: only the asymmetric tips moved
conclusion: the signal from the tip promotes growth and the light changes its distribution, lopsided replacement of the tip causes bending even under uniform light
1930: fritz went
goal: purify compound
model: concentrate auxin in agar blocks by putting cut coleoptile tips onto cubes, puts the agar block onto coleoptile stems, performs a bending assay
results: angle of curvature is proportional to amount of auxin in the block
conclusion: more cmpd = more bending
cholodny-went theory of tropic curvature
asymmetric light/gravity initiates lateral relocaiton of auxin, resulting in differential growth
ie. because of uneven light, aucin concentrates and causes bending
which side of a bent plant has more auxin?
shaded side
lateral relocation of auxin causes plant cells to:
elongate
auxin ___ cell elongation on shaded side
promotes
1930s: H.G. van der Weij
model: cut the middle of the coleoptiles and puts them upside down, replaced tip with agar block
results: even with the top being an agar block and the middle cut, if it is in the right direction, auxin will move. if upside down, auxin will NOT move
conclusion: polar transport of auxin (meaning auxin only moves from cells at the top towards the bottom, bottom cells are not specialized/equipped to move auxin)
gravitropism
growth response to a change in orientation relative to gravity
shoots grow ____ center of gravity and roots grow ___ center of gravity
away from ; towards
positive gravitropism
growing towards center of gravity, roots
negative gravitropism
growth away from center of gravity, shoots
auxin affects both:
gravitropism and phototropism
what scientist was polar transport of auxin?
HG van der weij
what scientist discovered phototropism/documented it?
darwin
