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Articles

Photosynthetic Activities of Spinach Leaf Protoplasts ¹

^a Research Institute for Biochemical Regulation, School of Agriculture, Nagoya University, Chikusa, Nagoya, 464, Japan

Photosynthetic activities of protoplasts isolated from spinach leaf (Spinacia oleracea L.) were investigated. The protoplasts were stable up to 9 hr, without loss of the original activity of CO₂ fixation (33-75 µmoles CO₂/mg Chl·hr) and light-dependent O₂ evolution (33-40 µmoles O₂/mg Chl·hr), when stored in 0.8 M mannitol-0.05 M N-tris (hydroxymethyl)-methylglycine-NaOH buffer, pH 7, at 4 C in dark. The optimum pH of 8.5 for CO₂ fixation reaction carried out in the present experimental condition employed is about the same as that reported for intact spinach chloroplasts. The CO₂ concentration for half-maximal rate of CO₂ fixation by protoplasts. "Km (CO₂)," were determined to be 19.8 µM (pH 7) and 42 µM (pH 8.5) and are similar to those observed for intact spinach chloroplasts. Protoplasts showed postillumination CO₂ fixation. Over-all results indicate that spinach protoplasts are as active as the intact plant leaf tissues in their photosynthetic activities.