Summary Plant physiology: Plant hormones

Summary Plant physiology – Emile Vancoppenolle
1. Introduction
2. Transport in plants
a. Transport introduction
b. Transport biophysics
c. Xylem
d. Phloem

3. Plant hormones
a. Gibberellins (GAs)
i. Introduction
- Tetracyclic diterpenes
- Dominant ones are GA1, GA3, GA4 and GA7
- Promotes stem elongation!
ii. Biosynthesis
- Each terpene consist of C5H8 backbone: isopentenyl diphosphate (IPP)
- Starting block is geranylgeranyl diphosphate made in chloroplasts

, - 4 classes of enzymes regulate GA synthesis from geranylgeranyl diphosphate:




KO and KAO are CYP proteins which take place in the E.R.

- C12 is further modified into different bioactive GA’s in the cytosol:




iii. Transport
- GA12 is the mobile, transportable gibberellin. Found in xylem and phloem

, iv. Signal transduction
- GID1: gibberellin insensitive dwarf 1
o GA receptor located in the nucleus
o DELLA is a negative regulator of GA responses (growth&development) by
binding transcription factors. When GID1 is bound to a GA, it will bind
DELLA which will then be ubiquitinated by the SCF complex. Proteasome
complex will degrade DELLA and thus the GA response will be
activated/stimulated. SPY (=SPINDLY) will glycosylate DELLA to stabilize /
activate it.




v. Physiology
- Photomorphogenesis
- Stem elongation
- Flower induction
- Parthenocarpic fruit (without seeds)
- Break seed dormancy
- …