Functional characteristics of intact chloroplasts isolated from mesophyll protoplasts and bundle sheath cells of maize.

A procedure was developed to isolate mesophyll and bundle sheath chloroplasts of a high degree of intactness and low cross-contamination. Light-induced (14)CO2 fixation of isolated chloroplasts was similar to that of protoplasts and cells in that it was low and was stimulated by the addition of exogenous substrates. O2 evolution was absent in both bundle sheath chloroplasts and cells. The flash-induced 515 nm absorbance change of intact mesophyll chloroplasts showed a biphasic rise, previously known to be a characteristic only of intact algae. With bundle sheath chloroplasts or cells, no 515 nm signal could be detected. In the presence of 10 μmol l(-1) phenazine methosulphate, bundle sheath chloroplasts exhibited a flash-induced 515 nm signal with a monophasic rise and amplitude comparable to that of the mesophyll chloroplasts. A similar signal was obtained with bundle sheath chloroplasts suspended in an extract prepared from the mesophyll tissue. Both the substrate stimulation of the CO2 fixation and the reconstitution of the 515 nm signal in bundle sheath chloroplasts by the mesophyll extract indicate the requirement of cooperation between the mesophyll and bundle sheath cells of maize leaves.