Metabolism of separated leaf cells: I. Preparation of photosynthetically active cells from tobacco.

Suspensions of mesophyll cells, prepared from tobacco leaves by treatment with pectinase, fixed CO(2) by photosynthesis. The products of carbon assimilation were similar for both cells and intact tissue. The cells sustained a constant fixation rate for 20 to 25 hours. For optimal CO(2) fixation, enzymatic maceration of the tissue was accomplished in 0.8 m sorbitol, but photosynthesis was optimal in 0.6 m sorbitol at pH 7 to 7.5. A hypertonic environment during maceration, which results in cell plasmolysis, is essential to maintain intact plasmalemmas and hence photosynthetically active cells. For sustained CO(2) fixation, light intensities below 500 foot-candles were required. Higher light intensities (to 1000 foot-candles) gave high initial rates of CO(2) fixation, but the cells bleached and were inactive on prolonged incubation. At pH 7.0 the bicarbonate concentration at maximal velocity of CO(2) fixation was about 1.5 mm and the apparent Km for bicarbonate was 0.2 mm.