groundbreaker
10 facts on...
by Philip McIntosh
ABSCISIC ACID
Abscisic Acis (ABA) functions in many plant developmental processes and can be involved in
stress responses as well. Philip McIntosh breaks down the importance of this plant hormone.
ABSCISIC ACID one one of the “classical” plant
hormones, and although it is an acid, it’s role in plants
is not directly related to regulating pH. It’s more
complicated than that (of course!).
SOMETIMES CALLED the stress hormone,
ABA is involved in many plant responses to
unfavorable conditions such as drought,
extreme cold, high soil salinity, and others.
ABSCISIC ACID was characterized
in the early 60s and is named after its
role in the process of abscission.
Abscission is the shedding of leaves
over winter by deciduous plants.
UNLIKE SOME other
plant hormones, which
exist in a myriad of
related chemical
forms, there is
essentially only one
abscisic acid (ABA).
ITS EFFECTS
on plant growth and
development are many,
including regulation of
the opening and closing
of stomata, stimulation
or inhibition of root
development, dormancy
of buds and seeds,
protection from dehydration,
and many others.
ABSCISIC ACID is part of the apical dominance system. As
auxin moves down from the plant apex, ABA moves up from the
roots to work in synergy to maintain the dormancy of lateral buds.
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groundbreakers
ABSCISIC ACID is also known for its
“anti” effects in relation to other hormones.
For example, auxin inhibits abscission,
ABA promotes it; gibberellins promote
elongation, ABA inhibits it.
STOMATA CLOSE
to limit transpiration
when ABA binds
to receptors on
stomatal guard cells,
triggering a cascade
of events leading to
loss of guard cell turgor.
SOME PLANT
pathogenic fungi also
produce ABA. Perhaps
this helps the fungus by
suppressing plant defenses.
ON THE other hand, it is also
thought that ABA stimulates the
activation of genes important in
plant wound responses.