page 32
EFFECTS AND PRACTICAL APPLICATIONS OF HORMONES/GROWTH SUBSTANCES - cont.

 
GIBBERELLIC ACID (GA)

1) Rosette or dwarf plants - lack of endogenous GA often causes

  • growth retardants - chemicals that block GA synthesis; are used in greenhouse and 

  •                                 bedding plant production to produce compact plants
2) Flowering - may cause bolting in biennials

3) Fruit size - increases size of seedless grapes

4) Bud dormancy - may overcome and substitute for cold treatment

5) Seed germination - may increase or speed up

6) Sex expression - favors staminate flower formation on monoecious plants
 

 

ETHYLENE

1) Fruit ripening - stimulates in many fruits, ex. banana

2) Flowering - triggers flowering in some bromeliads, ex. pineapple

3) Flower longevity - causes senescence (death) of cut flowers

4) Leaf abscission (leaf drop) - causes in some plants

5) Leaf epinasty (curling and contortion of leaves) - causes in some plants

6) Sex expression - favors pistillate flower formation on monoecious plants
 

 

ABSCISIC ACID (ABA)

1) Dormancy - causes bud or seed dormancy

2) Leaf abscission (leaf drop) - may cause in some plants

3) Stomata - causes stomata to close (a response to drought stress)