Carbon dioxide assimilation and photosystem II deficiency in bundle sheath strands isolated from C_4 plants

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The activities of Hill reaction and photosynthetic ^<14>CO_2 fixation in bundle sheath strands enzymatically isolated from millet (Panicum miliaceum) were 3-15 times as high as those observed in corn (Zea mays). In both preparations, 3-phosphoglycerate was the initial ^<14>CO_2 fixation product and the radioactivity was incorporated into sucrose and insoluble compounds (glucose-polymers) during the later period. After 20 sec of photo-synthetic ^<14>CO_2 fixation, the percent of ^<14>C incorporated into sugar phosphates in millet was about 3 times as high as that in corn, while in corn, the percent of ^<14>C in 3-phosphoglycerate was higher than that observed in millet throughout the experimental period. When ^<14>C-phosphoglycerate was added to the isolated bundle sheath strands, the rates of transfer of the radioactivity to dihydroxyacetone phosphate and sugar diphosphates in millet were significantly higher than those in corn. These results indicate that in the bundle sheath strands isolated from corn in which photosystem II activity is deficient, the reductive pentose cycle is impaired at the reduction step of 3-phosphoglycerate to glyceraldehyde phosphate due to the limited supply of NADPH through the photo-electron transport system. In contrast, the bundle sheath strands isolated from millet which have adequate photosystem II activity can carry out normal photosynthetic CO_2 fixation.
日本植物生理学会の論文