Carbon Dioxide Fixation by Guard Cell Protoplasts ofCommelina communis

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Abstract
Biochemical studies of epidermal tissue may not reflect metabolism of the guard cells which represent less than 5% of the tissue volume. Pure samples of guard cell protoplasts of Commelina communis were therefore used to investigate CO2 fixation rates and 14C-labelling patterns of metabolites in the light and the dark. Qualitatively, results were similar in most respects to those obtained in a previous study (Schnabl, 1980) for guard cell protoplasts of Vicia faba. CO2 fixation rates by guard cell protoplasts of C. communis were the same in the light and the dark but about 50 times lower than the values Schnabl obtained for V.faba. The 14C-labelling pattern of metabolites in C. communis was also similar in the light and the dark: over 60% of the total fixed was in malate with only 1% in sugar phosphates. Label was also detected in starch, aspartate, glutamate and citrate but not in glycollate as previously recorded in V. faba guard cell protoplasts. The results confirm the view that the reductive pentose phosphate pathway does not occur in guard cells of C. communis.

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