P2: Calcium-ABA signalling in guard cells

Question 1

Guard cells basics

Answer 1

• Control opening/closing of pore on surface of leaves
• Pore determines loss of CO2 and H20
• Control photosynthesis productivity
• Open by increasing turgor (increase water content), driven by osmotic ions; K+ and Cl- as well as organic malate ion

Question 2

ABA

Answer 2

• Induces an increase in [Ca2+]-cyt
• [Ca2+]-cyt inhibits K+in
• Also inhibits H+-ATPase
• Activates anion channels
• Activates VK

-> Depolarisation of PM activates K+-out

Question 3

CICR

Answer 3

• Calcium induced calcium release
• Occurs in this case by amplification of ABA-induced increase of [Ca2+]-cyt, example of second messenger system
  1. Influx of Ca2+ through PM Ca2+-permeable channels
  2. Increase in cytosolic [Ca2+]
  3. Activation of SV-channels (‘Slow-vacuolar’) in vacuolar membrane and release of Ca2+ from vacuole into cytoplasm

Question 4

Other second messengers for increase in cytosolic [Ca2+]

Answer 4

• IP3
• Cyclic ADP-ribose
• Sphingosine-1-phosphate
• Inositol hexakisphoshate

Question 5

EGTA

Answer 5

• Calcium chelator (i.e lowers free concentration of Ca2+ by sequestering it