beginner’s corner
“
IF A PLANT NATURALLY
LACKS GIBBERELLINS,
IT WILL BE DWARFED
IN STRUCTURE AND
STATURE. SOME
COMMERCIAL
PLANT GROWERS
INTENTIONALLY BLOCK
GIBBERELLINS FROM
BEING PRODUCED OR
RECEIVED IF A DWARF
PLANT IS DESIRED.”
Anyone who has ever trimmed a plant or shrub has
also seen the effects of this plant hormone. Auxin
is responsible for stem elongation at the tip of the
stems. This tendency of a plant to keep growing up
is called “apical dominance.” When these tips are
pruned or even unintentionally broken, the plant
then grows outward causing a stockier, usually
better and stronger branched plant.
Most auxins that are commercially used are
synthetic, due to the higher costs associated with
naturally occurring auxin. They are used for both
promoting growth as well as killing it. On fruit
trees, synthetic auxins are used to treat pruning
sites for sucker growth to prevent their return as
well as to prevent the setting of fruit. They are also
the primary compound in many popular herbicides.
They cause uncontrollable cell growth, like a
cancer, in plants and cause them to essentially
grow themselves to death. This is how 2,4-D works
so well for controlling broad-leafed weeds. On the
flip side, other types of synthetic auxins are the
primary component of rooting hormones for the
propagation of plant cuttings.
Gibberellins
Gibberellins (GAs) are the largest class of plant
hormones with more than 70 types of compounds,
both active and inactive. They also have the
distinction of being the first plant hormone to
be identified, studied, and understood by early
botanists. Like auxins, they are involved in the
elongation of stems. If a plant naturally lacks
GAs, it will be dwarfed in structure and stature.
Some commercial plant growers intentionally
block GAs from being produced or received if
a dwarf plant is desired. Several types of plant
growth regulators (PGRs) are GA blockers.
Gibberellins are also critical for fruit setting in
crops. It may be used in orchards and vineyards to
aid in the set of grapes and other fruits. They also
aid in the breaking of seed dormancy. This happens
naturally and is also employed by commercial
growers. Seeds that are traditionally difficult to
germinate due to a thick seed coat or other biolog-
ical factors are often treated with GAs to assist
in the breaking of their dormancy.
96
grow cycle