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Tryptophan-independent pathways of IAA biosynthesis:

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.

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Tryptophan-independent pathways of IAA biosynthesis:

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  1. Tryptophan-independentpathways 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 [15N] anthranilate fed  labeled IAA, not in tryptophan Glycosides of anthranilic acid and indole are accumulated in pericarp orange color is due to excess indole

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

  3. Conjugated (or bound) auxins– inactiveform ¤ 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:

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

  5. 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

  6. Auxin transport– the onlyplant growth hormone that has been clearly shown to be transported polarly ¤basipetaltransport: from the apical to the basal end via the vascular parenchyma cells of stems and leaves ¤acropetaltransport: 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

  7. Adventitious root formation – basipetal transport, gravity independent

  8. The characteristics of polar transport  in a cell-to-cell fashion, rather than via the symplast  require metabolic energy O2 deprivation and metabolic inhibitor the velocity is 5-20 cm/h diffusion rate: 7.2 cm/h; phloem translocation rate: 0.3-1.5 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.

  9. A chemiosmoticmodel – auxin polar transport Auxin pKa= 4.75

  10. Achemiosmoticmodel – 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) PINproteins, 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

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