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 – toward the source Negative gravitropism – 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 Conditions Season Examples day-neutral plant ( DNP ) not affected by day-night cycle anytime spring to fall tomatoes, dandelions, roses, corn, beans short-day ( SDP ) short days – LONG nights spring, fall ragweed, poinsettias, goldenrods, strawberries long-day plant ( LDP ) long days – SHORT 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