Plant “Behavior”

Plant “Behavior” How do roots “know” to grow down? How do stems “know” to grow up? Chemicals (hormones) that control, direct, and regulate plant growth Hormone: substance produced in one part of an organism and affects another part of the same individual

Plant Hormones Auxins – stimulate cell elongation (growth upward and downward) Cytokinins – stimulate cell division and growth of lateral buds (sideways growth) Cause dormant seeds to sprout Gibberellins – produce dramatic increases in size (particularly in stems and fruit) Ethylene – stimulates fruit to ripen

Plant Responses Tropisms – plant responses to external stimuli Gravitropism: plant response to gravity Involves auxins http://www.youtube.com/watch?v=mYZXax8V_L0 Phototropism: plant response to light http://www.youtube.com/watch?v=Ze8NV7cvW8k Thigmotropism: plant response to touch

Nastic Movements Plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus Example: Venus fly trap http://www.youtube.com/watch?v=O7eQKSf0LmY

Photoperiodism Responsible for the timing of seasonal activities, such as flowering and growth Regulated by a pigment that absorbs red light