COMPARATIVE STUDIES ON THE PHOTOSYNTHESIS OF HIGHER PLANTS : III. Differences in Response to Various Factors Affecting the Photosynthetic Rate between C-4 and C-3 Plants

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1) CO_2 compensation points of the plants tested correlate well with the leaf anatomy. Low CO_2 compensation plants had well-deve1oped VBS containing large and specialized chloroplasts but no plant with a high CO_2 compensation point possessed chloroplasts in the VBS. 2) CO_2 compensation points closely correlated with the major carboxylation pathway in photosynthesis. Low compensation plants fixed CO_2 via the C-4 pathway (C-4 plants) while high compensation plants carried out CO_2 fixation by the Calvin cycle (C-3 plants). 3) Close correlations could be established for the CO_2 compensation point, the major carboxylation pathway, and glycolate oxidase activity. Glvcolate oxidase activity was much higher in C-3 plants than in C-4 plants. On the other hand. dark respiration in C-4 plants was higher than that in C-3 plants. 4) TCA cycle activity in detached leaves was not inhibited to any large extent by illumination. 5) In C-3 plants, the release of ^<14>CO_2 from alanine-1-^<14>C increased with an increase in the ambient O_2 concentration ; whereas, radioactivity in the sugar fraction was quite small at all O_2 concentrations. In C-4 plants the release of ^<14>CO_2 was little affected by the ambient O_2 concentration while sugar formation was stimulated at high O_2 concentrations. This indicates that in C-3 plants CO_2 fixation is blocked at a high O_2 concentration, therefore, internal ^<14>CO_2 is released from the leaf without being refixed, but in C-4 plants internal ^<14>CO_2 can be efficiently refixed and metabolized to sugar by a combination of active PEP carboxylase and the 'Kranz type' of leaf anatomy.
社団法人日本土壌肥料学会の論文

COMPARATIVE STUDIES ON THE PHOTOSYNTHESIS OF HIGHER PLANTS : III. Differences in Response to Various Factors Affecting the Photosynthetic Rate between C-4 and C-3 Plants

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