Electrical Signaling Beyond Animals

Voltage-Gated K⁺ channels in Prokaryotes

ancient and highly conserved; bacteria can generate long-distance communication within biofilm colonies; communication via propagating waves of depolarizing K; positive feedback

Positive Feedback of Electrical Communication in Prokaryotes

metabolic trigger → release K; K depolarized neighboring cells ←→ release K

Membrane Potential (E_M)

movement of ions across membrane

Some of electrical signaling in prokaryotes predates

neurons

Algae

photosynthetic eukaryotes; not monophyletic group; brown, red, and green

Brown Algae

unicellular organisms (ex. Diatoms), Multicellular Kelp

Green Algae

land plants

Ca⁺² signaling is found in

all eukaryotes

Brown Algae Electrical Communication

respond to environmental distrubance with rapid changes in Ca²⁺

Diatom Electrical Communication

use Na and Ca voltage-gated channels to spontaneously generate APs

Non-Plant Green Algae Electrical Communication

move in response to light by triggering light-gated ion channels → Ca²⁺ flows into cell → flagellum movement

Plant Electrical Communication

via ions; mechanisms to move in repsonse ot external stimuli; Action Potential (AP) & Slow Wave Potential (SQP)/Variation Potential (VP); long distances & short

Where do long distance Action Potentials travel in plants?

phloem bc cells are alive

Where do long distance Slow Wave/Variation Potentials travel in plants?

xylem bc dead cells

Where do short distance Potentials travel in plants?

plasmodesmata

Animal Neurons Resting Potentials

Na⁺ (out)/K⁺ (in) pumps (need ATP); K⁺ leak channels; range: -60 to -70 mV

Plant Cells Resting Potentials

H⁺ pumps → need ATP, pump H⁺ out & hyperpolarize cell; K⁺ leak channels depolarize cell; range: -80 to -200 mV

Plant Action Potentials are characterized as

all-or-nothing; refractory periods; size of peak and duration may vary by species; typically fired in response to non-harmful stimulus (ex. temperature, light, mechanical, electrical)

Steps of Plant Action Potential

stimulus triggers Ca²⁺ ions to flow in, reversibly shut down H⁺ pumps & activate voltage-gated Cl^- channels; Cl^- ions leave cell → Action Potential; Ca²⁺ pumps pump Ca²⁺ out → reactivates H⁺ pumps and they repolarize cell

Animal Action Potential Trigger

neurotransmitter

Plant Action Potential Trigger

touch, temperature, light, change

What ion depolarizes an animal cell?

gaining Na⁺ for AP

What ion depolarizes an plant cell?

loss of Cl^- for AP

What ion repolarizes an animal cell?

loss of K⁺ (via voltage gated channels)

What ion repolarizes a plant cell?

reactivation of H⁺ pumps (via Ca²⁺ being pumped out)

Travel speed of animal Action Potential

~100 m/s

Travel speed of plant Action Potential

~ 1 mm/s

Plant Slow Wave Potentials

slow and long-lasting depolarization; non-self-perpetuating; can trigger APs; typically fired in response to harmful stimulus (ex: wounds, flame)

Electrical Communication in Fungi

spontaneous AP-like activity in hyphae that respond to external stimuli; could aid in coordinating behavior of complicated mycelial networks or allow communication with symbionts