IN-SITU IMMUNOFLUORESCENT LOCALIZATION OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE IN MESOPHYLL OF C-4 DICOTYLEDONOUS PLANTS/

The location of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC O) in the leaf mesophyll of some dicotyledonous C-4 plants was confirm ed by immunofluorescent labelling. The anti-RuBPCO immune serum was ob tained by inoculating a rabbit with commercially obtained RuBPCO. Spec ificity of these antibodies was tested by immunodiffussion, immunoelec trophoresis, and Western blotting. Fresh hand-cuts of leaves from dico tyledonous C-4 plants, Amaranthus caudatus, A. dubius, Gomphrena globo sa, and Portulaca oleracea, were incubated with the conjugated anti-Ru BPCO immune serum and then with a commercial FITC-anti-rabbit IgG conj ugate. Nerium oleander was used a control C-3 plant pattern and Zea ma ys as a C-4 plant pattern. The immunofluorescent label was distributed in both mesophyll and bundle sheath in all the C-4 plants tested. It is an unequivocal proof that in the C-4 dicotyledonous plants the RuBP CO is not only located in the chloroplasts of the bundle sheath cells but also in the chloroplasts of the mesophyll cells. In these plants t herefore, the C-4 pathway cannot exclusively be viewed as an intercell ular level concentration mechanism. In the mesophyll cytoplasm, phosph oenolpyruvate carboxylase traps CO2, while in the mesophyll chloroplas ts, RuBPCO operates with atmospheric CO2 and CO2 from the C-4 decarbox ylation step at an intracellular level, which could mean a significant energetic economy. The CO2 from photorespiration could be saved and r eincorporated. Location of RuBPCO in the mesophyll and/or bundle sheat h chloroplasts is a matter of inter- and intracellular compartmentatio n which makes another variation of C-4 photosynthetic pathway possible .