Actin can reversibly assemble into filaments that consist of two helices of actin subunits

TLS Online TPP Program

#Id: 10272

#Unit 6. System Physiology – Plant

Guard cell volume depends on H+-ATPase. Orthovanadate, an inhibitor of the H+-ATPase,

inhibits this swelling

TLS Online TPP Program

#Id: 10273

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 10274

#Unit 6. System Physiology – Plant

Changes in osmotic potential of guard cells required for stomatal opening in the morning are mediated by potassium and its counterions, whereas the afternoon changes are mediated by sucrose.

TLS Online TPP Program

#Id: 10275

#Unit 6. System Physiology – Plant

Three major distinct metabolic pathways that can supply osmotically active solutes to guard cells have been clearly characterized:

1.The uptake of K+ and Cl– from the apoplast, coupled to the biosynthesis of malate2– within the guard cells.

2. The production of sucrose in the guard cell cytoplasm from precursors originating from starch hydrolysis in the guard cell chloroplast

3. The production of sucrose from precursors made in the photosynthetic carbon fixation pathway at the guard cell chloroplast

TLS Online TPP Program

#Id: 10276

#Unit 6. System Physiology – Plant

The enzyme that converts violaxanthin to zeaxanthin is an integral thylakoid protein showing a pH optimum of 5.2.

TLS Online TPP Program

#Id: 10277

#Unit 6. System Physiology – Plant