XVI International Botanical Congess

Marked modulation in vivo by external weak acids or alkalizing agents of cell sap pH and PEP carboxylase (PEPC) activity occurred in leaves of C4 plants. When leaf discs of Alternanthera pungens, a C4 plants, were preincubated in 7.5 nM NHCl (alkalizing agents), the pH of the cell sap increased by 0.3 unit, while the activity of PEPC doubled up, compared to those in the cell sap from control leaf discs (preincubated in Ph 8.5 buffer). The sensitivity of PEPC of ?-malate (a feedback inhibitor) decreased marginally as a result of cytosolic alkalization. The pH of cell sap and PEPC activity decreased by 0.4 unit and 50% respectively, when leaf discs were incubated in weak organic acids. The technique of base loading can be a useful tool to study the regulation of PEPC in leaves of C4 species.