Homework #1 is posted and due 9/17 Bonus #1 is posted and due 10/24 Discussions started this week

Why so many steps?

Multiple steps allow for signal specificity. Different relay molecules lead to different responses

Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals

Calcium is a common effector. Cytoplasmic calcium levels are normally low.

During signal transduction, calcium can be released into the cytoplasm: Perception

During signal transduction, calcium can be released into the cytoplasm: Transduction

During signal transduction, calcium can be released into the cytoplasm: Response

During signal transduction, calcium can be released into the cytoplasm

General model of Ca++ signaling

General model of Ca++ signaling

Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals

Ca++ is involved in many responses

Ca++ is involved in signal transduction for responses of: in Plants Development Cold Guard cell closing Osmotic shock Light Fungal infection Touch Pollen tube growth Wounding… in Animals Neurons Muscle movement Wounding Development Fertilization Hormones … How can there be specificity?

Everything has its place…

Some Ca++ channels have specific effectors associated with them: Micro-domains Ikeda, Science 12 Oct 2001 Vol 294:318-319

Root nodules: Nitrogen fixation

Bacteria and Plants Symbiosis

Signaling between bacteria and plants

A biphasic Ca++ response to Nod factor: 1nM Nod 10nM Nod A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984

A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984

Everything has its place…

2 hypotheses about how Ca++ signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506

Photosynthesis: Plants can make sugar using energy from the sun, water from the ground, and CO2 from the air.

Stomata regulate gas exchange: CO2 in, O2 and water out H2O H2O

Stomata open closed

Opening and closing of stomata

Ca++ fluxes in guard cells in response to hormone or stress that cause stomatal closing. Wildtype vs. det3 and gca2: mutants that fail to close stomata following treatment Fig 5. Sanders et al., The Plant Cell, S401–S417, Supplement 2002

2 hypotheses about how calcium signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506

Signal Transduction External Stimulus Internal Effector… Effector Response Perception (by receptor) Stimulus

Homework #1 is posted and due 9/17 Bonus #1 is posted and due 10/24 Discussions started this week