Chapter 19 Auxin: the growth hormone Animal hormones: are synthesized and secreted in one part of the body and are transferred to specific target sites in another part of the body via the blood stream. endocrine and paracrine hormones kinds: proteins, small peptides, amino acid derivatives, and steroids. Plant hormones: have profound effects on development at vanishingly low concentration (  1 mM). kinds: auxins, gibberellins, cytokinins, ethylene, abscisic acid brassinosteroids, jasmonic acid, salicylic acid, polypeptide systemin Plant growth regulators: promoters and inhibitors

Auxin: the first growth hormone to be discovered in plants ¤ Plant cell expansion ¤ Viability ¤ Stem elongation ¤ Apical dominance ¤ Root initiation ¤ Fruit development ¤ Oriented, tropic growth or phototropism

6 mm Cell elongation

The active growth-promoting substance can diffuse into gelatin block; Bioassay: a measurement of the effect of a known or suspected biological active substance on living material.

Auxin: to increase or to grow the elongation of oat coleoptile sections H2OH2O + auxin

Natural vs. synthetic auxins indole herbicide Active auxins: a negatively charged carboxyl group a fractional positive charge on aromatic ring 1930

The definition of auxins: the compounds with biological activities similar to those of IAA, including the ability to promote cell elongation in coleoptile and stem sections, cell division in callus cultures in the presence of cytokinins, formation of adventitious roots on detached leaves and stems, and other developmental phenomena associated with IAA action. Adventitious roots: roots that arise from structures other than roots, such as stems or leaves.

Promote lateral and adventitious root formation – even though auxin inhibit the primary root elongation Lateral roots: above the elongation and root hair zone and originate from small groups of cells in the pericycle. Adventitious roots: originating from non-root tissue via their cell division activity

Quantitative auxins: ¤ Bioassay ¤ Enzyme-linked immunosorbent assay ¤ Mass spectrometry – gas chromatography: ~ pg

Auxin synthesis sites: Hydathodes: the special pores associated with vein endings at the leaf margin The shoot and root apical meristems, young leaves, developing (young) fruits and seeds (06?) a differentiating vascular strand The margins of young leaves A synthetic auxin-sensitive DR5 promoter + a GUS reporter

Tryptophan-dependent pathways of IAA biosynthesis: Brassicaceae, Poaceae, Musaceae bacteria multiple pathways  important for development