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Title: Incorporation of newly accumulated carbon into leaf protein
Author: Collin, Hamish Auld
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1965
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Carbon forms approximately fifty percent of protein and in the growing leaf this carbon may be derived from a number of sources. These possible sources are carbon skeletons of the organic nitrogen imported from the root, sucrose imported from more mature leaves and autonomous assimilate. The contribution by the last source to protein synthesis in the young bean leaf was subsequently examined in the period from leaf unfolding to full expansion. The 2nd T.F. leaf at different stages of expansion was exposed to 01402 for a limited period then, using the 014 in protein, the amounts of protein synthesized from newly assimilated carbon were calculated. The rate of synthesis of this protein was then compared with the rate of synthesis of total protein in the leaf. Newly assimilated carbon appeared to make only a small contribution at early expansion but it increased from a proportion of less than 1 to 10-22% at late expansion. Under high concentration of 01402 this proportion showed a considerable increase suggesting that the rate of protein synthesis, either-nett synthesis or synthesis as calculated from C14 values in protein,was stimulated by a rapid assimilation rate. The ability of imported assimilate to act as a source of carbon for protein synthesis in the young leaf was also investigated. After exposing the let T.F, to 01402 for a short time, then allowing a distribution of assimilate, the C14 in the protein of the 2nd T.F. was measured. Imported assimilate was shown to contribute to protein. synthesis in the young leaf, but the supply of carbon ceased when the young leaf was half expanded and had become independent of the lower leaves. Protein synthesis in the mature leaf was demonstrated by exposing 2nd Tas at all stages of maturity to C1402. During this period from full expansion to senescence, the protein content was either constant or declining. The incorporation of C14 labelled carbon into protein was considered, therefore, to represent protein turnover, which was estimated to be 0.03f0 of the total protein per hour. Further evidence for a turnover in the mature leaf was provided by the change in the C14 in protein of an attached leaf, left intact for a period of four weeks after the assimilation of C1402. In the first 24 hours the C14 in protein increase from less than of the total C14 in the leaf to 6% declined in the succeeding 24 hours.
Supervisor: Porter, Helen K. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available