Auxin Flashcards
Darwins concluded that there was a signal that was produced in the – and moved to the growth zone
tip
Went showed that a chemical could be collected from the coleoptiles which cause – in the absence of light
bending
chemical identity of auxin
indole-3-acetic acid (IAA)
molecular distance of – between a fractional positive charge on the aromatic ring and a negatively charged carboxyl group
0.5 nm
IAA biosynthesis is associated with rapidly dividing and growing tissues, especially –
shoots
primary synthesis sites
shoot apical meristems and young leaves
IAA is transported into the cytosol and nucleus where it binds to a receptor and the complex regulates –
gene expression
roots and shoots show – polarity which is independent of orientation with respect to gravity
axial
polar transport is the principal cause of an auxin gradient extending from
shoot tip to root tip
polar transport proceeds from cell to cell: exits through plasma membrane – across cell wall and enters next cell through plasma membrane
diffuses
polar transport requires
metabolic energy
velocity of polar transport is faster than diffusion but slower than –
phloem translocation
major site of polar transport is the –
vascular parenchyma tissues
polar transport depends on proton pumping out of the cell and into the cell wall
chemiosmotic model
IAAH diffuses into the cell or IAA- is pumped into the cell by – via an H+ IAA- symporter
secondary active transport
once IAA- enters the cytosol, it accumulates and then – occurs via special transporters driven by the negative membrane potential (relative to the cell wall, which has accumulated H+)
efflux
important components of the auxin efflux carrier complex
PIN proteins
auxin promote growth in stems and coleoptiles while inhibiting
root growth
for excised tissues, addition of auxin stimulates growth after a lag period of about
10-12 minures
full response requires – and above optimum concentration auxin becomes inhibitory
sucrose
auxin stimulates growth by increasing the – of the cell wall
extensibility
m
wall extensibility
Y
yield threshold
proteins in cell walls that loosen cell walls under acidic pH by weakening the hydrogen bonds between polysaccharides in the wall
expansins
growth toward light and is expressed in all shoot and some roots
phototropism
coleoptile stimulated by light will transport IAA –
laterally
once IAA reaches shaded side it is transported – to the elongation zone, stimulating cell elongation (by acidifying the cell wall)
basipetally
acceleration of growth on the shaded side and slowing of growth on the illuminated side causes –
curvature toward light
gravitropism also involves – redistribution of auxin
lateral
gravitropism causes a rapid differentiation in the expression of auxin-stimulated mRNA –
small auxin up-regulated RNAs (SAURs)
dense plastids detect gravity
amyloplasts = statoliths
statoliths fall through the cytoplasm and trigger the stimulus by either interacting with the cytoskeleton or by exerting pressure on the – at the bottom of the cell
ER
stimulus is triggered occurs in shoot’s – which is a layer of cells that surrounds the vascular tissue or in root cap
starch sheath
– cells causes redistribution of auxin
gravity sensing
– concentrations of auxin in the upper side of a horizontal root causes more rapid growth and bending downward
lower
