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Photosynthesis of Ulva sp.: III. O₂ Effects, Carboxylase Activities, and the CO₂ Incorporation Pattern

Sven Beer and Alvaro Israel
Plant Physiology
Vol. 81, No. 3 (Jul., 1986), pp. 937-938
Stable URL: http://www.jstor.org/stable/4270075
Page Count: 2
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Abstract

Ulva, a common green seaweed, performs at the biochemical level as a typical C3 plant. Over 90% of label was found in glycerate 3-phosphate following a 3 second 14C pulse in the light, and the label was subsequently transferred to sugars. Also, the level of ribulose-1,5-bisphosphate carboxylase activity in crude extracts was about 10 times higher than that of phosphoenolpyruvate carboxylase. Concerning gas exchange, photosynthetic rates of Ulva showed no O2 sensitivity, indicating that photorespiratory CO2 losses are repressed as in C4 plants. This apparent anomaly could be explained by the efficient HCO3 - uptake system of Ulva which might concentrate CO2 to the chloroplasts, thus suppressing the oxygenase activity of ribulose-1,5-bisphosphate carboxylase.

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