6) Polar Cell Growth and Polar Auxin Transport

how is plant cell growth anisotropic?

unequal growth in shape or size

plant cell growth is mediated by internal pressures (turgor pressure), and cell wall loosening

internal pressure is generated by osmosis

cell wall loosening is regulated by cellulose microfibril arrangement and cell wall modification

explain root growing

epidermis layer on the outside

root hairs can be form one single cell growing

increase surface area to get water

what are pavement cells

protrusions on the cell as it grows

in leaf epidermis, the cells are shaped like a jigsaw puzzle (lots of surface area to glue them together)

under epidermis, kidney shaped cells intermix with pavement cells, these are guard cells (center is pore called stoma)

what are trichomes

spikey structures, look like a tree, can be multicellular

different types of trichomes, can have glands on the top carrying toxic gas released when bug bites into plant

explain mutation in root cells

MT disorganization, so cellulose microfibrils will be randomly aligned, causes isotopic growth (not targeted growth anymore)

less strength provided by shorter cellulose microfibrils

explain how mutations can be temperature sensitive?

some mutant proteins are normal at 21°C, this is the permissive temperature

at 31°, the protein misfolds, making it nonfunctional

MAPs are lethal when mutated

to test, grow plants at permissive temperature, then increase temp, look for proteins that only show mutant phenotype at specific temperature

details on arabidopsis flower

hermaphroditic, self-pollination can occur

each seed has a style associated with it (the hairs on corn are the styles of corn)

TT = transmitting tract, growing down towards the ovules

fertilization in arabidopsis

double fertilization

as pollen tube grows down, 2 sperm cells, 1 fertilizes egg, the other fertilizes the central cell

egg develops into embryo, becomes diploid (haploid + haploid = diploid)

central cell develops into endosperm, becomes triploid (diploid + haploid = triploid)

types of pollen tube guidance

mechanical, physiological, chemotrophic

what is funicular guidance

pollen tube is chemically directed towards the egg

how does pollen tube grow

plus ends are directed towards tip
golgi and vesicles move towards plus tip via the filaments

formin on plus ends, adding G-actin right on the end
new filaments have plus ends pointed back towards the old end

what is reverse fountain flow

new filaments flowing towards tip on the outside, and flow back towards the old end in the middle

bring golgi and vesicles to tip, filaments that are derived from the tip are moving things back

what are LURES

LURES: peptide, signal that directs pollen tip growth
interaction between LURE and receptor triggers other events
produced by synergid cells, right next to egg
rearrangement of actin filaments, get redirected and make a turn, directing towards the opening (micropyle)

what is CHx21/23

shows K+ entering pump/leaving tip and H+ leaving pump/entering tip

causes pH drop

calcium in, protons out

what is auxin

plant hormone produced at growing tip of shoot

acts as an inhibitor to repress lateral bud activity (apical dominance)

the further from the tip the buds are, the less repression, and buds can grow (if you remove the tip, you remove the source of auxin and allow the buds to grow

what is polar auxin transport

auxin flow through the root, moves from cell to cell

mediated by transporters located in plasma membrane

movement of auxin in roots is downwards in endodermis and cortex

what are PIN proteins

auxin efflux carriers

located at the bottom (basal) area of the cells

in epidermis, located at the top (apical), which drives movement upwards

PINs are polarized, and provide directional movement of auxin from cell to cell

dynamic movement of PINs cycling between plasma membrane and endosomes. maintains polarized localization

recycling and redepositing the PIN proteins at the bottom

role of actin in vesicle movement

acts to keep proteins in correct place (keeps PIN at basal end of cell)

what is IAA

indole acetic acid, natural form of auxin

explain auxin movement

auxin moves from intracellular space to adjacent cell

in cell wall, pH is low (5.0), within cytosol, pH is high (7.0)
facilitates passive diffusion of auxin into the cell

between cells, pH is low, auxin is non-ionized
lower pH, will pick up a proton (in non-ionized form)
can move through membrane passively

once inside cell, auxin becomes ionized (deprotonated), will want to stay in aqueous form

how is methanic acid toxic to cells

at low pH, compounds are non-ionized and pass into cell

once in cell, become ionized and stay within cell

plant machinery inside cell will break compounds downs