Download Chapter 19 Auxin: the growth hormone Animal hormones

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
H2 O
+ auxin
the elongation of oat coleoptile sections
Natural vs. synthetic auxins
Active auxins: a negatively charged carboxyl group
a fractional positive charge on aromatic ring
1930
indole
herbicide
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:
The shoot and root apical meristems, young leaves,
developing (young) fruits and seeds (06?)
The margins of young leaves
Hydathodes:
the special pores associated with vein
endings at the leaf margin
A synthetic auxin-sensitive DR5
promoter + a GUS reporter
a differentiating
vascular strand
Tryptophan-dependent pathways of IAA biosynthesis:
bacteria
Brassicaceae,
Poaceae,
Musaceae
multiple pathways
 important for
development