Signal Processing

The process by which a stimulus from the environment is received by a sensory cell, triggering signal transduction, release of a cell-cell signal, signal reception by a target cell, and a change in the target cell's behavior.

Possible events in a signal transduction cascade

Conformational changes of a receptor, changes in binding partners, protein modifications (phosphorylation), activation of second messengers, opening/closing of ion channels, and activation/repression of transcription/translation.

Auxin

A plant hormone that controls cell expansion by regulating the stability of the cell wall.

Acid-growth hypothesis

Auxin receptors increase the number of proton pumps in the cell membrane, decreasing pH in the cell wall, which activates expansins.

Expansins

Proteins that loosen cell wall cross-links, enabling osmotic pressure to expand the cell.

Phototropins

Blue-light activated kinases that phosphorylate targets to control the locations of auxin transport proteins.

Phytochromes

Red light receptors that control physiological and developmental events, such as seed germination, shoot elongation, photosynthesis, and flowering.

Pr form

The default or “ground” state of phytochromes that absorbs red light and converts into Pfr.

Pfr form

The active form of phytochromes that absorbs far-red light and converts back to Pr, triggering biological processes.

Photoperiodism

A plant's developmental response to changes in day length.

Plant Hormones

Small organic molecules that are diffusible in tissues, transported through xylem and phloem, and have diverse effects on plant growth and development.

Auxin

A plant hormone produced in shoot apical meristems and young leaves that promotes apical dominance, fruit development, inhibits abscission, stimulates vascular tissue differentiation, and adventitious roots.

Cytokinins

Plant hormones produced in root apical meristems that stimulate cell division, promote seed germination, influence shoot/root formation ratio, inhibit stem elongation, stimulate axillary bud growth, and delay leaf senescence.

Gibberellins

A class of plant hormones produced in apical meristems, immature seeds, and anthers that stimulate stem elongation and regulate fruit growth.

Ethylene

A gaseous plant hormone produced in all plant organs that promotes fruit ripening, leaf abscission, senescence, and maintains the apical hook.