Transcript Plant Repsonses - pptx

Plant Responses
Chapter 31
Section 1
PLANT HORMONES
Auxins
Apical Dominance
Apical Dominance
Gibberellins
Ethylene
Cytokinins
Section 2
PLANT MOVEMENT
Tropism
• Tropism is a growth response
• Positive tropism = growth toward stimulus
• Negative tropism = growth away from
stimulus
Phototropism – growth in response to light
• Positive
phototropism –
toward it
• Negative
phototropism – away
from it
Thigmotropism – growth in response to
touch
• Positive
thigmotropism –
toward it
• Negative
thigmotropism – away
from it
Gravitropism – growth in response to gravity
• Positive gravitropism • Negative gravitropism
– toward the source
– away from source
Chemotropism
• Plant growth in response to a chemical
NASTIC
MOVEMENTS
Nastic Movements
• Movements by a plant that are responding
to a stimuli ( a tropism )
• The direction they move is not important
– no positive
– no negative
Thigmonastic Response
• A response to touch
• Due to a drop in turgor pressure
– Water pressure decrease – leaf evaporation
Thigmonastic Response
Venus flytrap
Prayer plant
Mimosa plant
Nyctinastic Response
• A daily response to light and dark cycle
• Bean plant
• Roses
• Tulips
Section 3
SEASONAL RESPONSES
Photoperiodism
• Plant response to seasonal changes in the
length of day (or night)
• Response is due to a pigment that is light
sensitive
• Affects:
– flowering
– dormancy start for buds
– formation of storage organs
Day and Night Length
• A key factor in flowering
• Many species have a “critical night length”
Day and Night Length
• Today – botanists use the phrases:
Short-Day plant (SDP)
Long-Day plant (LDP)
• But the night length determines flowering
Short-Day Plants
• SDP flower when the days are short
– This really means the nights are long
• Those conditions occur only in the:
Spring and Fall
Long-Day Plants
• LDP flower when the days are long
– This really means the nights are short
• Those conditions occur only in the:
Summer
Seasonal Responses to Light
TYPE OF PLANT
FLOWERING
FLOWERING
CONDITIONS
SEASON
day-neutral plant
not affected by
anytime spring to
( DNP )
day-night cycle
fall
EXAMPLES
tomatoes,
dandelions,
roses, corn, beans
ragweed,
short-day
short days – LONG
( SDP )
nights
spring, fall
poinsettias,
goldenrods,
strawberries
long-day plant
long days – SHORT
( LDP )
nights
summer
asters, irises
Fall Colors
• Changing fall color is due to
photoperiodism
• Change due to day length – temperature

Fall Colors
• As nights become longer
– Leaves stop producing chlorophyll
– Orange (carotenoids) and yellow
(xanthophylls) become visible – by default
The End
Chapter 31