Transcript Hormonal Control in Plants

Hormonal Control in Plants
Requirements for Growth & Reproduction
2008
Solar tracking (heliotropism)
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Some plants orientate their leaves
perpendicular to the sun’s rays. This
maximises their absorption of sunlight and
photosynthesis.
Plants in desert climates orientate their
leaves parallel to the sun’s rays, hence
decreasing leaf temperature and water loss
through transpiration.
Ethylene
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Gaseous hormone produced in many plant
parts
 fruit ripening
 promotes leaf, fruit and flower
abscission
Abscicic Acid
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produced in terminal buds and maturing
seeds (stress hormone)
 closes stomata (pores in leaves)
 inhibits growth
 enforces seed dormancy
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In Autumn, phytochrome
levels change.
The plant responds by
producing abscisic acid at the
petiole (leaf attachment
point).
Chlorophyll is moved from
the leaf into the stem, so
leaves go yellow/red.
Petiole cells soften until the
leaf drops off.
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Dicots can grow
from either:
 Apical
buds/meristems
(the top of the
plant)
 Lateral
buds/meristems
(buds at
branching
points)
Apical dominance
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When the apical bud grows more quickly
than the lateral buds, the plant grows into a
tall slender shape.
The apical bud produces auxin, which
inhibits growth at lateral buds.
If the apical bud is pruned, the lateral buds
are no longer inhibited and the plant grows
into a low bushy shape.