#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
