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 HormoneStimulates 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 StimulusHormoneResponse LightAuxins move to shaded side of plant Cells on shaded side elongate causing plant to bend towards light

Thigmotropism StimulusHormoneResponse Touching a solid object Auxin and ethylene Tendrils and stems coil, allows vine to climb, increasing interception of sun

Gravitropism S timulus H ormone Response GravityAuxinsRoots – 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 StimulusHormoneResponse Chemical???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