Beer–Lambert law might not be the case any more in samples with high absorbance.

TLS Online TPP Program

#Id: 10280

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 10281

#Unit 6. System Physiology – Plant

ABA signaling in guard cells is largely mediated through the second messenger Ca2+.

TLS Online TPP Program

#Id: 10282

#Unit 6. System Physiology – Plant

ABA causes stomata to close by reversing the accumulation of potassium salts in guard cells and inducing the conversion of sugars into starch. 

The resulting fall in solute concentration leads to loss of water from the guard cell into the apoplast by osmosis, a fall in guard cell turgor, and closing of the stomatal pore. 

TLS Online TPP Program

#Id: 10283

#Unit 6. System Physiology – Plant

Increased [Ca2+]cyt activates plasma membrane anion efflux channels, and these two effects combine to depolarize the membrane. Membrane depolarization closes voltage‐sensitive K+ in channels but opens K+ out channels. 

TLS Online TPP Program

#Id: 10284

#Unit 6. System Physiology – Plant

K+in channels are inhibited directly by the rise in [Ca2+]cyt. Overall, therefore, the increase in [Ca2+]cyt causes the net efflux of anions and K+ from the cell, leading to a fall in guard cell turgor.

TLS Online TPP Program

#Id: 10285

#Unit 6. System Physiology – Plant

The elevated calcium levels in the cytosol then activate CDPKs that phosphorylate and activate RBOH proteins which generate more ROS.