Respiratory Loss of Recently Assimilated Carbon in Wheat |
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Authors: | MORGAN, C. L. AUSTIN, R. B. |
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Affiliation: | Plant Breeding Institute Trumpington, Cambridge CB2 2LQ |
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Abstract: | A series of experiments was undertaken to assess the amountof respiration associated with the growth of wheat at differentstages. Plants (or in some cases just the flag leaf) were labelledwith 14CO2 and the amount of 14CO2 respired during the subsequent48 or 72 h was measured. The evolution of 14C, expressed asa percentage of the amount initially assimilated (referred toas the R/A value) was used as a measure of the overall efficiencyof dry matter production. Respiratory 14CO2 evolution from labelledplants was most rapid in the first 12 h after labelling, thereafterdeclining rapidly. Evolution was also more rapid following labellingsat the end of the light period (dusk) than at the beginningof it (dawn). The R/A values were greatest (42 and 50 per centrespectively for dawn- and dusk-labelled plants) for young plantsand least (13 and 28 per cent respectively) for plants duringmid grain filling. When flag leaves, as distinct from wholeplants, were labelled, R/A values were lower still (9 and 21per cent respectively), indicating that flag leaf assimilatewas used efficiently in grain production. The calculated minimum R/A for the formation of grain material(10 per cent protein, 90 per cent starch) was 6.2 per cent.That the experimentally determined values were greater thanthis is attributed to the turnover of carbon in enzymes, toother maintenance processes, and possibly to the operation ofthe pentose phosphate pathway of glucose oxidation. R/A valueswere lower in those plants labelled at the beginning than thoseat the end of the photoperiod. This was considered to be a consequenceof refixation of respiratory 14CO2 during the light. The higherR/A values found for young plants were considered to be a consequenceof the greater percentage of 14C translocated to the roots (rootsbeing unable to refix respired CO2) and of greater turnoverof enzymes associated with more active metabolism. Triticum, wheat, respiration, carbon assimilation, carbon loss, grain-filling |
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