Download Other Plant Hormones - NCEA Level 3 Biology

Other Plant
Hormones
Gibberellins
• There are now more than 60 known
gibberellins.
• These cause rapid growth of the
internodes on stems.
– The internode is the region between the
points where the leaves are attached.
– Dwarf plants are often short because
they do not produce enough gibberellin
to form long internodes.
Gibberellins
• These hormones are produced in young
leaves and buds.
• They cause flowering in long-day plants
even when they are kept in short-day
conditions.
• They cause flowering in biennials that
normally need a period of chilling
(vernalisation)
Gibberellins
• They help to mobilise the endosperm
(food reserve) in cereal seeds.
• They promote the germination of a wide
variety of seeds that would otherwise be
hard to germinate.
• They are becoming increasingly important
in industry – e.g. they increase the size of
seedless grapes when sprayed on them.
The Cytokinins
• These are produced mainly in the roots
• They regulate the process of cell division.
• These hormones are found in coconut
milk, fruits, seeds and roots.
Promoting Cell Division
• Cytokinins promote cell division in intact
plants and tissue cultures.
– Relatively high conc of auxin to
cytokinin produces roots in a tissue
culture.
– Higher proportions of cytokinins to
auxins produces buds and leaves.
– Roughly equal concs make callus
tissue (undifferentiated tissue)
Cytokinins
• Cytokinins slow down the process of aging
(senescence) in plants, if applied to
leaves it can prevent the yellowing of
mature leaves in autumn and their
dropping (abscission).
Abscisic Acid
• In general, this functions as an inhibiting
hormone acting against auxin,
gibberellins and cytokinins.
• It plays a role in abscission.
• Dormant buds have relatively high levels
of ABA which drop as spring approaches
• Some dormant seeds also contain
relatively high concs of ABA
Abscisic Acid
• It also seems to have a role in helping
plants to withstand drought conditions, by
affecting transpiration and closing guard
cells of the stomata.
Ethylene Gas
• “one rotten apple spoils the barrel”
• A ripening apple gives off ethylene gas
that ripens adjacent fruit.
• Commercially ethylene gas is important:
– It influences the ripening of fruit
– It helps the harvesting of berries,
causing them to drop.
– It helps the rubber in rubber trees to
flow for longer.
Ethylene Gas
– It increases the sugar content in sugar
cane.
– It promotes flowering of pineapples.
– It accelerates the aging of tobacco
leaves.
Florigen
• The flowering hormone.
• This has not been isolated but there is
evidence that there is a hormone which
induces flowering.