Tryptophan-independent pathways of IAA biosynthesis: Orange pericarp (orp) mutant of maize inactive tryptophan synthase a true tryptophan auxotroph IAA level is 50-fold higher than those of wild-type plant [ 15 N] anthranilate fed  labeled IAA, not in tryptophan Glycosides of anthranilic acid and indole are accumulated in pericarp orange color is due to excess indole

Trp-dep. or Trp-indep. varied with tissues and developmental stages.

Conjugated (or bound) auxins – inactive form ¤ types: low MW compounds conjugated Glc, myo-inositol, amide high MW compounds glucan (7-50 Glc per IAA), protein depend on the specific conjugating enzymes, environmental factors such as light and gravity (conjugation formation or hydrolysis) ¤ Physiological functions transportation: IAA-myo-inositol storage: protection:

Photodestruction/ riboflavin Turn off light during extraction Conjugation and degradation of IAA: Oxindole-3-acetic acid Oncidium

The distribution of IAA ¤ is regulated by pH ¤ major in cytosol and chloroplast ¤ in tobacco cells free IAA conjugated IAA cytosol 2/3 1 chloroplast 1/3 0 exclusively

Auxin transport – the only plant growth hormone that has been clearly shown to be transported polarly ¤ basipetal transport: from the apical to the basal end via the vascular parenchyma cells of stems and leaves ¤ acropetal transport: toward the tip (in the root) via phloem transport (major), xylem parenchyma of the stele more than one mechanism (pathway) is responsible for the distribution of auxin Donor-receiver agar block method independent of gravity

Adventitious root formation – basipetal transport, gravity independent

The characteristics of polar transport  in a cell-to-cell fashion, rather than via the symplast  require metabolic energy O 2 deprivation and metabolic inhibitor  the velocity is 5-20 cm/h diffusion rate: 7.2 cm/h; phloem translocation rate: m/h; xylem translocation rate: 4 mm/s (14.4 m/h).  the specific protein carriers of plasma membrane involve only for active auxins, both natural and synthetic.

Auxin pKa= 4.75 A chemiosmotic model – auxin polar transport

 Auxin influx (or uptake) (  pH +  E) (p. 477R) (a) passive diffusion: protonated IAAH (b) secondary active transporter: 2H + -IAA - symporter efficiency is greater than simple diffusion e.g., AUX1, a permease-type auxin uptake carrier aux1 mutant: agravitropic growth for root  Auxin efflux (a) auxin anion efflux carrier: (  E) PIN proteins, are integral membrane proteins, localized at the basal ends of conducting cells (b) P-glycoproteins (PGPs) : ATP-dependent transporters, belonging to the multidrug resistance/P-glycoprotein (MDR/PGP proteins) are uniformly distributed can independently and synergistically catalyze auxin transport with PINs a BR2 gene encodes a PGP