Hormones Communication among cells, tissues and organs Hormones in animals: -molecules interact specifically with receptors -production and reception are separated (transport through blood stream, target organ) - proteins (growth hormone) - small peptides (insulin) - amino acid derivatives (adrenalin) - steroids (estrogen) - organ specific - specific responses - effective at low concentrations

Phytohormones Communication among cells, tissues and organs Hormones in plants: -molecules interact specifically with receptors? -production/reception are not always separated (transport through vacular tissue, air, diffusion, ?) - secundary compounds (ABA, GA) - nucleotide derivatives (cytokinin) - amino acid derivatives (auxin) - steroids (brassinosteroids) - multiple responses - not organ specific - effective in very low concentrations (>10 -6 M)

Auxin transport and plant polarity

Campbell, 1998 Phototropism

Auxin effects on fruit development

Avena coleoptile system

Classical auxin experiments

Indole-3-acetic acid (IAA) So that is what auxin looks like!! What was the material diffusing from Went’s agar block?

Indole-3-acetic acid How and where is auxin made? Auxin is synthesized in meristems, young developing leaves and fruits

How and where is auxin made?

Auxin transport is polar (goes into one direction) and is independent of gravity. Root growth stimulated in inverted bamboo sections by auxin moving from what was the top. If auxin is a mobile signal, how is it transported?

Auxin effect on embryo development Auxin effect on vascular tissue

wt mp control NPA

Auxin and root growth A: control B: IAA C: 2,4-D D: NAA E: IBA

Ciesielski 1878 Root bending Pea root bending following gravivector Root tips ablated with acid Root tips viable Darwin 1880 The power of movement in plants

Auxin and the root cap

Auxin and root gravitropism

Campbell, 1998 Phototropism

DR5::GUS reporter gene for auxin light Taiz/Zeiger, 2002 Lateral IAA movement increased IAA causes bending

Mutant over produces auxin in roots Vascular tissue Visualization of auxin Auxin promotes lateral root formation Auxin promotes vascular differentiation

Taiz & Zeiger, 2002 Apical dominance depends on auxin production in the SAM

PIN1 mutations show extreme apical dominance

Taiz & Zeiger, 2002 control IAA Cell wall elongation assay of hypocotyl segments IAA induces an increase in the elasticity of the cell wall by reducing its pH. This allows the cells to expand easier

Acid growth hypothesis  acidic buffers induce cell elongation without auxin  neutral buffers inhibit auxin-induced cell elongation  inhibitors of H + -ATPase inhibit auxin-induced cell elongation ?

How could the acid growth hypothesis work?? auxin control ? ? ?