Rates of Photosynthesis in Characean Cells

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Abstract
Photosynthetic 14C fixation by Characean cells in solutions of high pH containing NaH14CO3 gave a measure of the ability of these cells to take up bicarbonate (H14CO3−). Whereas cells of Nitella translucens from plants collected and then stored in the laboratory absorbed bicarbonate at 1−1.5 μμmoles cm−2 sec−1, rates of 3−8 μμmoles cm−2 sec−1 were obtained with N. translucens cells from plants grown in the laboratory. Influxes of 5–6 μμmoles cm−2 sec−1 were obtained with Chara australis, 3–8 μμmoles cm−2 sec−1 with Nitellopsis obtusa, and 1−5 μμmoles cm−2 sec−1 with Tolypella intricata. It is considered that these influxes represent the activity of a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H14CO3− uptake would be masked by rapid diffusion of 14CO2 into the cells: the four Characean species fixed 14CO2 at maximum rates of 30−40 μμmoles cm−2 sec−1 (at 21° C).