LOCALIZATION OF SUCROSE-PHOSPHATE SYNTHASE AND STARCH IN LEAVES OF C-4 PLANTS

The activity and intercellular distribution of sucrose-phosphate synth ase (SPS, EC 2.4.1.14) were determined in fully expanded leaves from a range of C-4 plants. In Zea mays L. and Atriplex spongiosa F. Muell., SPS was located almost exclusively in the mesophyll cells. In other s pecies, SPS was found in both cell types, with the activity in the bun dle sheath cells ranging from 5% of the total leaf activity in Echinoc hloa crus-galli (L.) Beauv. to 35% in Sorghum bicolor Moench. At the e nd of the light period, starch was found only in the bundle sheath cel ls in all of the species examined. There appears to be little correlat ion between C-4-acid decarboxylation type and the location of sucrose and starch synthesis in the leaves of C-4 plants.