Chapter 19 Auxin: the growth hormone

Animal hormones: are synthesized and secreted in one part of the body and are transfer

red 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

H2O + auxin

Natural vs. synthetic auxins

indole

herbicide

Active auxins: a negatively charged carboxyl group

a fractional positive charge on aromatic ring1930

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 hai

r zone and originate from small groups of cells in the pericycle.

Adventitious roots: originating from non-root tissue v

ia 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