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
