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

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Abstract
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.