In situ Immunofluorescent Labelling of Ribulose-1,5-Bisphosphate Carboxylase in Leaves of C3 and C4 Plants

Abstract

Antibodies raised to wheat and spinach ribulose-1,5-bisphosphate carboxylase (RuP2Case) have been used to locate the enzyme in hand-cut leaf blade transections of 40 C3 and C4 species, and one crassulacean acid metabolism (CAM) plant by immunofluorescence (using the indirect technique). The sample includes species from seven plant families, both monocotyledons and dicotyledons. In C3 and CAM species, specific fluorescence is associated with chloroplasts of all leaf chlorenchymatous cells when labelled with anti-RuP2 Case, while in species with 'classical' C4 leaf anatomy RuP2 Case is located almost exclusively in 'bundle sheath' ['Kranz' or 'photosynthetic carbon reduction' (PCR)] cell chloroplasts. Ten C4 species exhibit various types of 'non-classical' C4 leaf anatomy (Alloteropsis, Aristida, Arundinella, Cyperus, Fimbristylis, Triodia and Salsola types) and, for all but one of these types, immunofluorescent labelling of RuP2 Case provides the first direct experimental evidence of a cellular compartmentation of photosynthetic carbon metabolism and of the location of PCR compartments. Leaves of two Atriplex C3/C4 hybrid individuals and of Panicum milioides, a putative C3/C4 intermediate, exhibited a C3 antibody labelling response.