Download Plant Hormones

Plant Hormones
Darwin’s idea
Plant hormones are chemical
messengers of homeostasis
They are:
• Organic compounds
• Effective at very low concentration
• Synthesized in one part of the plant and
transported to another
• Interactive with specific target tissues to cause
physiological responses
There are five major groups of plant hormones
Make a table for the following
information
Hormone
Auxins
Stimulates
Auxins
• Stimulates:
– cell elongation
– cell division
– differentiation of phloem and xylem
Abscisc Acid
• Stimulates:
– closure of stomata
– seeds to synthesize storage proteins.
– induction and maintenance of dormancy.
– gene transcription in response to wounding
Cytokinin
• Stimulates:
– cell division
– morphogenesis
– growth of lateral buds
– leaf expansion
– chlorophyll synthesis.
Ethylene
• Stimulates
– shoot and root growth and differentiation (triple
response)
– leaf and fruit abscission (falling off plant)
– flower opening
– fruit ripening
Gibberellins
• Stimulate
– stem elongation
– enzyme production (a-amylase) in germinating
seeds
Plant movement
• Is a response to environmental stimuli such as:
light, gravity and mechanical disturbances.
• Movements fall into two groups:
– tropisms and nastic movements.
TROPISM
• Plant movement determined by direction of
an environmental stimulus.
• Movement toward an environmental stimulus
is called a positive tropism and away is called
negative tropism.
• Each kind of tropism is named for its stimulus
• Example; positive phototropism
Phototropism
Stimulus
Light
Hormone
Auxins
•move to
shaded side
of plant
Response
Cells on
shaded side
elongate
causing
plant to
bend
towards
light
Thigmotropism
Stimulus
Hormone
Response
Touching a
solid object
Auxin and
ethylene
Tendrils and
stems coil,
allows vine
to climb,
increasing
interception
of sun
Gravitropism
Stimulus Hormone Response
Gravity Auxins
Roots – positively
gravitropic – auxins
accumulate on lower
side of root cells
inhibits elongation, so
roots grow down.
Stem – negatively
gravitropic – auxins
accumulate on
lower side of stem
stimulate
elongation so stem
grows up
Chemotropism
Stimulus
Chemical
Hormone
???
Response
Plant will
grow
towards or
away from
source.
Task
• Read the information provided and make a
chart to show two types of Nastic movement:
– Thigmonastic
– Nyctinastic