Chapter 20 Gibberellins: Regulators of plant height

¤ 1950s, the second groups of hormones

¤ “foolish seedling” or bakanae

¤ a chemical secreted by Gibberella fujikuroi, GA3

¤ C19 or C20, defined by their chemical structure, more than 125 (136)

¤ http://www.plant-hormone.info/gibberellin_ nomenclature.htm.

¤ GA1 identified from Phaseolus coccineus, 1958

¤ GAx, x is the number in the order of their discovery

¤ only a few are biologically active

Physiological functions: increase in plant height

particularly in genetically dwarf and rosette plants, but no effect on the genetically very

tall plants

Stem thickness, leaf size

A pale green color of the leaves

Bolting:

Stem growth

4-day-old rice seedlings (dwarf) were treated

with increasing amount of GA3 for 5 days, bioassay

Dosage dep.

Stem injected the previous summer with GA4/GA7

mixture in aqueous ethanol

14-week-old

Spray GA3 some 8 weeks earlier

GAs regulate the transition from juvenile to adult phases

Conebud formation

Physiological functions:

promote pollen development and tube growth

influence floral initiation and sex determination

Tassel + GA female (pistillate) induction,

suppress stamen (anther) development

In dicots, GA seems to have the opposite effect

GA / ABA

GA-deficient mutant+ GA3

- GA3

p. 522

Physiological functions:

promote fruit set: apple

promote parthenocarpy

promote seed germination: to overcome the dormancy

Commercial applications:

fruit production

alleviating compaction

delay senescence: citrus

malting of barley

increasing sugarcane yield

plant breeding

biosynthesis inhibitors

lodging (used Cycocel), shrub plantings

seedless grapes

Cyclization

B ring: 6 5CH3 COOH

The first GAThe precursor of other GAs

homeostasis

GA20ox, GA3ox:

negative feedback regulation

GA2ox:

positive feed-forward

regulation

Fe2+

ascorbate require

GA20 GA5 GA3

active

inactive