Assessing the Degree of C4 Photosynthesis in C3-C4 Species Using an Inhibitor of Phosphoenolpyruvate Carboxylase

Abstract

An analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP), was used to inhibit phosphoenolpyruvate carboxylase and, therefore, assess the contribution of the C(4) pathway to photosynthesis in detached leaves of several C(3)-C(4) 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 O(2) for the C(3)-C(4) species Panicum milioides, Moricandia arvensis, and Neurachne minor or the C(3) species Flaveria pringlei. However, when leaves of Flaveria linearis (C(3)-C(4)), Flaveria brownii (C(4)-like), and Flaveria trinervia (C(4)) were fed 4 millimolar DCDP, photosynthesis was reduced 32, 60, and 90%, respectively. Photosynthetic inhibition by 210 milliliter per liter of O(2) 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 C(3)-C(4) species into species including Panicum, Moricandia, and Neurachne whose reduced photorespiration occurs without any C(4) photosynthetic involvement and species of Flaveria in which C(4) photosynthesis contributes to CO(2) assimilation.