Plant hormones

HormonesHormones

• from Gr. to excite • natural chemical

messengers transported to target cells

• minute concentrations = substantial change

• growth regulators

Plants respond to stimuliPlants respond to stimuli

Plant hormones coordinate growth, Plant hormones coordinate growth, development and responses to stimulidevelopment and responses to stimuli

Tropisms

• growth responses

• organs curve towards (+) or away from (-) a stimulus

• ex. phototropism, thigmotropism, gravitropism

Studies on phototropismStudies on phototropism

• towards or away from light

• differential growth of cells on opposite sides of a shoot or coleoptile

• cells on darker side elongate faster than those on the light side

• experiments by Darwin and son and FW Went

• due to auxin distributions

Went experiment