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.