1. §2 Gibberellins (赤霉素） I: Discovery
Late 19th and early 20th century, Japanese rice farmers found “Bakane disease or foolish seedlings”-恶苗病, -elongated seedlings with slender leaves and stunted roots. Severely diseased plants die whereas plants with slight symptoms survive but produce poorly developed grain, or none at all..
1926, Japanese scientists Kurosawa (黑泽英一)identified the cause: infected by a fungus: Gibberella fujukuroi (Sawada,1912: 赤霉菌）.
1938， Japanese scientists Teijiro Yabuta(薮田贞次郞) isolated and crystallized the active material: gibberellin （GB：赤霉素）。
After World War II, known to the west ( Cross in England in America isolated gibberellic acid from fungal cultural filtrate).
1958，MacMillan isolated GB from immature bean seeds。
Till now, 136GBs were identified from plants, fungi and bacteria。

2. Foolish disease of rice
Normal rice seedlings “foolish rice seedlings”

3. II: Structure
GB is a diterpene，consists of 4 C5 units (19 or 20 carbons).
All gibberellins are derived from the ent-gibberellane skeleton.
Gibberellins all contain carboxylic groups and are thus acid。
GA3 = gibberellic acid, is the first GB structurally characterised 。

4. Hydroxylation at this position (C2) will inactivate the molecule.
All active GAs have COOH in this position (C7).

5. 3-b-hydroxylation 1,2-unsaturation 3-b,13-dihydroxylation
are more active. 17
GAs with 20 carbons are called C20 GA. There are also C19 GAs. Generally C19 GA is more active than C20 GA, although more than 1/3 of all GAs are C20 GA.

6. GA1 and GA20 are both C19 GAs. They have the highest biological activity and they are also two of the most important GAs.

7. GA3 is C20 GA. It can be readily isolated from fungus.
Because it is the most accessible GA so we understand the action of GA3 better than the rest.

8. III: Distribution, forms and transport
Ubiquitous in plant kingdom, GA1 most active in plants, GA3 in ferns and GA3 is from fungi.
In fast growing organs such as immature seeds and fruits.
Forms：
Free GB (active)
Conjugated GB (inactive, transport and storage)：with glucose and amino acids.
Transport：
No polar transport, can transport through xylem and phloem.

9. IV: Synthesis （ISOPRENE UNITS 5C异戊二烯）
Gibberellins are terpene（萜） derivatives or terpenoids（萜类化合物：15000 in plants such as sterols, carotenoid, ABA, CTK, BR and so on).
Biosynthesis of GB are divided into three stages
The first stage: synthesis of IPP (isopentenylpyrophosphate,异戊烯基焦磷酸）
because IPP has two synthesis pathways, therefore, GB has two synthesis pathways
1). MVA (mevalonic acid：甲瓦龙酸）) pathway in cytosol
2). MEP (methylerythritol-4-phosphate: 甲基赤鲜糖醇-4-磷酸）pathway
in chloroplasts
The second stage: GGPP synthesis from IPP
the third stage: GA synthesis from GGPP
Possible detail steps ：
MVA→→→ent- kaurene(内根－贝壳杉烯) in plastid
Inhibited by AMO 1618, Phosphon D
ent- kaurene→→→GA12-7-aldehyde in ER
inhibited by Cycocel
GA12-7-ald→→→gibberellins in cytosol

10. 第一阶段：
IPP合成
MVA pathway

11. MEP pathway

12. 第二阶段：
Synthesis of GGPP
from IPP
GGPP
（牻牛儿牻牛儿基焦磷酸）

13. 第三阶段： Synthesis of GAs from GGPP （GA12-7-醛） (GGPP) (内根-贝壳杉烯）
(AMO-1618, CCC, Phospho-D)
(Phosphon-D)
(内根-贝壳杉烯）
(Ancylmidol)
嘧啶醇
（GA12-7-醛）

14. IPP can also be converted to other important molecules in cytosol and chloroplasts

15. Luciferase reporter construct for GA 20-oxidase
3.　Site: quick growing parts
Luciferase reporter construct for GA 20-oxidase

16. V: Functions Stimulates stem elongation
GB is more effective to dwarf plants。
GB stimulates stem elongation by：
Promote cell division: GA increases the transition from G1 to S and shortened S。
Increase flaccidity of CW.
Stimulate the hydrolysis of starch and hence increase osmosis water absorption
GB only increases internode length without increasing nodes.

18. 2 GA1 appears to be the gibberellin that promotes stem extension
Figure Relation between stem elongation and GA1 level

19. 2. induce the synthesis of α-amylase and promote germination
1. GB in embryo
2. gibberellins diffuse to aleurone layer
3. aleurone is induced to synthesize and secrete alpha amylase and other hydrolases into the endosperm
4. starch and other polymers are degraded to small molecules
5. solutes are absorbed by scutellum and transported throughout the growing embryo

22. GA-stimulated release of a-amylase from barley half-seeds.
Figure 16.12
10 nM GA

23. 3. Break off dormancy of organs
immerse potato cuts with 1ppm GB for 5~6min, the dormancy can be relieved.
4. Stimulate flowering of juvenile plants
5. Substitute for long daylength to stimulate flowering of LDP under SD such cabbage, radish and carrot .
6. Substitute low temperature to stimulate flowering in biennial plants.
left：control
center：10ug GA3 for 4 weeks,
right：low temp. for 6 weeks
carrot

24. 7. Promote cucumber ♂ flowers
8.Induce Parthenocarpic (seedless) Fruit (grape)
9. Delay senescence in leaves and citrus fruits .

25. Applications
increase size of grapes (spray at time of blooming and fruit set stage)
increase distance between grapes in a cluster to minimize fungi/disease
Breweries - increase starch digestion for malting process
Delay senescence - spray on fruit like naval oranges
celery stalk elongation
sugar cane - increased growth and yields

27. Homework: Please describe the recent molecular model
of GA signal transduction.