Measurement of guard-cell respiration rates using Cartesian-diver technique

Dark respiration rates of guard-cell protoplasts of Commelina communis L. were measured over a temperature range (15-30° C) using a Cartesian-diver microrespirometry technique. Measurements were made using a few microliters of suspension medium containing between 400 and 3 700 protoplasts. Respiration rates were approximately linear for at least 1 h at all temperatures. Respiration rates increased rapidly between 20 and 25° C to relatively high levels (6.11·10(-6) μmol O2 h(-1) protoplast(-1)=1259 μmol O2 mg(-1) chlorophyll h(-1)=22.97 μmol O2 mg(-1) protein h(-1)) with no further increases above this temperature. Respiration rates were much lower in protoplasts 15-16 h old than in freshly prepared ones indicating considerable deterioration of their viability over this time period.