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Plant Growth
Hormone Function and
Tropisms
Primary Meristems
Whether they are involved in primary or secondary growth, all plant
cells and tissues arise from three primary meristems*:
• protoderm
• ground meristem
• procambium
*Meristem: plant tissue that remains embryonic as long as the plant lives,
allowing for indeterminate growth
Specialized Tissues in Plants
 Plant
Growth
 Meristems
– tissues
responsible for growth
 Undifferentiated
 Apical
cells
Meristem
 Produce
growth
increased length
 Differentiation
 Cells
will assume roles in
the plant
 Flower
 Starts
Development
in the meristem
Growth Hormones
(Regulation)
 Plants
produce chemical substances
called hormones that inhibit or promote
growth.
 Common plant hormones are….




Inhibitors
Cytokinins
Gibberellins
Auxins
that work with auxins to stimulate cell
Cytokinins
division.
 Hormones
Gibberellins
 Hormones
that stimulate cell elongation,
premature flowering, and breaking of
dormancy.
Auxins
 Hormones
that speed plant growth by stimulating cell
enlargement.
Tropisms
 A tropism
is a growth response involving bending
or curving of a plant part toward or away from an
external stimulus that determines the direction of
movement
 Response toward the stimulus is positive, and
response away from the stimulus is negative
Phototropism
 Phototropism
is the growth of stems of plants
toward light - it is probably the best known of
the plant tropisms - phototropism is caused by
elongation of the cells on the shaded part of
the plant - so that entire plant bends or curves
toward the light
 This growth pattern is caused by the hormone
auxin - auxin migrates to the shaded part of the
plant and stimulates increased cell growth and
elongation on the shaded part of the plant
Gravitropism
 Gravitropism
is a response to gravity - if a
seedling is placed on its side, the root will
curve to grow downward and the shoot will
curve to grow upward
 Auxin may play a role in the response of
shoots
Gravitropism in plants
Thigmotropism
 Thigmotropism
is response to touch or contact
with a solid object - this is most commonly seen in
tendrils, modified leaves or stems depending on
the species.
 the tendrils wrap around any object they come in
contact with and so enable the plant to cling and
climb.