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Title: The sites of synthesis of photosynthetic product in tobacco leaves
Author: Roberts, Godwin Rajendran
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1969
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The intracellular distribution of radioactivity assimilated during short periods of photosynthesis in 14CO2 was determined after separation of the chloroplasts from the rest of the cell using non aqueous density gradient centrifugation. ADPG, starch, UDPG and sucrose were found to be predominantly synthesised inside the chloroplast. The non chloroplastic UDPG and sucrose were, however, labelled rapidly. After shorter periods of photosynthesis (5 to 30 sec.) most of the radioactivity assimilated was incorporated into the phosphate esters, glycine and serine. The radioactive phosphate-esters formed during 30 sec photosynthesis were mainly inside the chloroplast but glycine and serine were almost equally labelled inside and outside the chloroplast. The higher specific activity of glycine and serine suggest that these compounds may be synthesised inside the chloroplast. It was evident from these experiments that 25 to 30% of the assimilated radioactivity is probably metabolised via the glycollate pathway. There was a considerable conversion of chloroplast phosphate esters to glycine and serine if leaves were illuminated for short periods in ordinary air after Photosynthesis in 14CO2. Prolonged illumination resulted in the rapid movement of radioactive glycine and serine out of the chloroplast. The radioactive phosphate esters moved out relatively slowly. There was also a decrease in the specific activity of chloroplast glycine and serine, probably due to the synthesis of inactive compounds inside the chloroplast. The general conclusions were supported by experiments where assimilation of radioactive carbon dioxide was followed by periods of light and dark. Glycine was converted to serine in the dark. Reillumination in ordinary air resulted in the formation of radioactive glycine from phosphate esters. There appeared to be some conversion of serine to glycine under certain conditions. The synthesis of glycine and serine inside the chloroplast and the ready permeability of the chloroplast membrane to these amino acids resulted in their rapid movement out of the chloroplast. The importance of these observations in relation to the possible role of glycine and serine in the transport of photosynthetically assimilated carbon out of the chloroplast is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available