Atp Synthesis During Photosynthetic Induction Studied with a Very High Time Resolution
Biologicheskie Membrany: 1994 11:283-288
Subcellular ATP/ADP ratios as well as 3-phosphoglycerate (PGA) and triosephosphate (TP) levels were determined in barley protoplasts using rapid fractionation by membrane filtration. When the protoplasts were illuminated, ATP production started virtually momentarely. The ATP/ADP ratio in the chloroplasts increased from 1 to 4 within 2 s. Also, the export of ATP to the cytosol was very rapid giving a dramatic increase in the cytosolic ATP/ADP ratio within a few seconds, the maximum was reached after about 15 s. In contrast to ATP production, about one minute elapsed until oxygen evolution started and the maximum rate was reached after four to five minutes. The ATP/ADP ratios in the chloroplasts and the cytosol stayed very high until photosynthetic oxygen evolution started and then decreased gradually when the photosynthetic rate reached its maximum. In photorespiratory and non-photorespiratory conditions the subcellular ATP/ADP ratios were very similar during photosynthetic induction, also in both cases PGA decreased and triosephosphates increased in the chloroplasts as well as in the cytosol. In steady-state the subcellular ATP/ADP ratios were higher in photorespiratory conditions as compared to non-photorespiratory conditions.
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