Rates of Photosynthesis in Characean Cells

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Abstract
A study has been made of photosynthetic 14CO2 fixation by isolated ‘mature’ internodes of Nitella translucens. Experimental conditions were similar to those used in studies of the ionic relations of these cells. Maximum rates of photosynthesis were 33–40μμmoles CO2, fixed per cm2 of surface area per second (equivalent to 12–15 /xmoles fixed per mg chlorophyll per hour). l4CO2 fixation was inhibited to the dark level by 3(3,4,dichlorophenyl)-1, 1-dimethylurea (at 0-6 μM or 10μM) and by the uncoupler carbonyl cyanide-m-chlorophenylhydrazone (SμM). The presence of imidazole or ammonium sulphate (both of which uncouple ATP production in vitro) did not result in an inhibition of 14CO2 fixation. These results are discussed in relation to published work on solute uptake by Nitella translucens. During photosynthesis there was rapid movement of 14C-labelled organic compounds out of the chloroplasts. 14C-labelled sucrose, ammo-acids, and sugar phosphates were found in samples of vacuolar sap.