ASSESSING THE DEGREE OF C-4 PHOTOSYNTHESIS IN C-3-C-4 SPECIES USING AN INHIBITOR OF PHOSPHOENOLPYRUVATE CARBOXYLASE

An analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxy-phosphinoylmethyl-2-propenoate (DCDP), was used to inhibit phosphoenolpyruvate carboxylase and, therefore, assess the contribution of the C4 pathway to photosynthesis in detached leaves of several C3-C4 intermediate species. There was no effect of 4 millimolar DCDP on apparent photosynthesis or on inhibition of apparent photosynthesis by 210 milliliters per liter of O2 for the C3-C4 species Panicum milioides, Moricandia arvensis, and Neurachne minor or the C3 species Flaveria pringlei. However, when leaves of Flaveria linearis (C3-C4), Flaveria brownii (C4-like), and Flaveria trinervia (C4) were fed 4 millimolar DCDP, photosynthesis was reduced 32, 60, and 90%, respectively. Photosynthetic inhibition by 210 milliliter per liter of O2 was also significantly increased in 4 millimolar DCDP-fed leaves of F. linearis and F. brownii but not in F. trinervia when compared with control values. These results with DCDP clearly demarcate C3-C4 species into species including Panicum, Moricandia, and Neurachne whose reduced photorespiration occurs without any C4 photosynthetic involvement and species of Flaveria in which C4 photosynthesis contributes to CO2 assimilation.