CH 31 Notes
Plant hormones help coordinate growth, development, and responses to stimuli.
- hormone - signaling molecule that binds to receptor and triggers responses
- plant growth regulator - are like plant hormones to help control/regulate plant physiological processes
- prduced in very low concentrations
Discovery of Plant Hormones
- growth response that results in plant organs curving away or toward a stimuli = tropism
- phototropism = toward or away from light
- shoots - positive phototropism
- roots - negative phototropism
- phototropism only occurs when tip is exposed to light
- only works when chemicals can pass thru to the tip and coleoptile
- asymmetric distribution of certain substances that may act as growth inhibitors which are more concentrated in lighted side of a stem not shaded side
Survey of Plant Hormones
- major classes of plant hormones - auxin, cytokinins, gibberellins, brassinosteroids, abscisic acid, and ethylene
- any chemical substance that promotes elongation of coleoptiles.
- produced in shoot tips and transports from tip to base.
- effects = stimulate cell elongation and regulating plant architecture
Role of Auxin in Cell Elongation
- moves from shoot tip down to region of cell elongation --> binds to receptor in plasma membrane
- acid growth hypothesis - proton pumps play major role in growth response of cells to auxin by stimulating H+ pumps (increases voltage and lowers pH of cell wall which activates expansins that break cross links between microfibrils and loosens the cell wall & increases membrane potential allows more ions into the cell --> more water intake and +turgor)
- rapidly alters gene expression so that new cells of cell elongation to make new proteins quickly
Auxin's Role in Plant Development
- polar transport region of auxin = central element controlling spatial organization (pattern...